European Polymer Journal 48 (2012) 1001–1025

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European Polymer Journal

journal homepage: www.elsevier .com/locate /europol j

Feature Article

Recent advances in honeycomb-structured porous polymer films preparedvia breath figures

Pierre Escalé 1, Laurent Rubatat 1, Laurent Billon ⇑, Maud Save ⇑IPREM Equipe de Physique et Chimie des Polymères, UMR 5254 CNRS, Université de Pau et des Pays de l’Adour, Hélioparc, 2 Avenue du Président Angot, 64053 PauCedex, France

a r t i c l e i n f o a b s t r a c t

Article history:Received 2 December 2011Received in revised form 23 February 2012Accepted 1 March 2012Available online 21 March 2012

Keywords:HoneycombBreath figurePorous polymer filmSelf-assemblyHybridsCopolymer

0014-3057/$ - see front matter � 2012 Elsevier Ltdhttp://dx.doi.org/10.1016/j.eurpolymj.2012.03.001

⇑ Corresponding authors. Tel.: +33 540175014.E-mail addresses: laurent.billon@univ-pau.fr (L.

univ-pau.fr (M. Save).1 These authors contributed equally to this work.

Since its introduction in 1994, the preparation of ordered porous polymer films by thebreath figure (BF) method has received a considerable interest. The so-called ‘‘honeycomb’’(HC) films exhibit a hexagonal array of micrometric pores obtained by water droplet con-densation during the fast solvent evaporation performed under a humid flow. The mainfocus of this feature article is to describe the recent advances in the design of honeycombpolymer films by the BF process. We first review the recent studies related to the honey-comb film formation through the exploration of different parameters such as the relativehumidity, the polymer concentration, the drying rate, the substrate or the role of interfacialtension. The influence of the architecture and microstructure of the polymer is examinedthrough examples. In this contribution, a special attention is given to the recent articlesfocused on the preparation of elaborate functional honeycomb-structured polymer filmsobtained via the simple BF method. In this context, we review the preparation of hierarchi-cal HC films showing either sub- or super-structure, the formation of hybrid HC films byself-assembly of nanoparticles or in situ generation of the inorganic matter, the fluores-cence in HC films introduced either by a fluorescent polymer or by fluorescent chemicalgroups, the elaboration of biomaterials from HC films decorated by glycopolymer and/orshowing sensing ability and finally the design of functional polymeric surfaces with eitherstimuli-responsive or superhydrophobic properties.

� 2012 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10022. Formation of honeycomb patterned polymer films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003

2.1. Influence of polymer architecture and/or microstructure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10032.2. HC film structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004

3. Hierarchical structures in polymer films using breath figure method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007

3.1. HC and substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10073.2. HC and superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1008

4. Highly structured hybrid honeycomb polymer films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1009

4.1. Self-assembly of polymer/nanoparticle blends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10104.2. In situ formation of the hybrid honeycomb films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1011

. All rights reserved.

Billon), maud.save@

1002 P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025

4.3. Polymer honeycomb films as templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10124.4. Highly structured hybrid honeycomb films by a non usual process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1014

5. Fluorescence in honeycomb polymer films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10156. Biomaterials based on honeycomb polymer films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016

6.1. Honeycomb films decorated with glycopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10166.2. Biosensing from HC polymer films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1018

7. Functional materials based on honeycomb porous films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019

7.1. Smart honeycomb porous surface responsive to an external stimuli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10197.2. Superhydrophobic honeycomb porous films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1021

8. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1021References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022

1. Introduction

Since the first study published by François et al. in 1994[1] with star shaped polystyrenes (PS) and poly(para-phe-nylene)-b-PS block copolymers, the formation of honey-comb (HC) structured polymer films by the breath figure(BF) approach has received considerable interest due tothe simple, inexpensive, and robust mechanism of patternformation [2–3]. Breath figures occur when water vaporcondenses onto either cold solid [4] or liquid [5–6] sur-faces. Steyer et al. [5] suggested that growth of breath fig-ures on liquids evolves through three stages. In the initialstage, there is no strong interaction among the water drop-lets, and the diameter (D) of the droplets increases withtime (t) by a power law of D � t1/3. In the crossover stage,water droplets are separated by a thin liquid film, andthe whole surface has a maximal coverage with low disper-sity of droplet diameters. The last stage is the coalescence-dominated stage where the surface coverage is high andconstant. Coalescence accelerates the growth and thediameter (D) grows in proportion to time (t) as D � t.Limaye et al. [6] investigated the influence of the natureof the solvent on the time development of the averagewater droplet diameter. For the case of benzene, two sep-arate regimes of growth law were clearly observed (D � ta)

Fig. 1. Schematic representation of the honeycomb poly

with a � 0.3 (single droplet growth, no coalescence) anda � 0.95 (coalescence dominated), while in the case ofchloroform, a rather uniform a � 0.5 dependence is seen,reflecting the role of coalescence over the entire time do-main. When using the appropriate polymer solution,breath figure can be fixed in the polymer matrix creatingporosity via the imprint of the water droplets [1–3,7].The formation of porous polymer films with honeycomb(HC) morphology proceeds via the water droplet genera-tion on the cold surface of the evaporating polymer solu-tion and the subsequent self-organization of the waterdroplets into an ordered hexagonal lattice (see Fig. 1).The regular stacking of the water droplets is favored bythe Bénard–Marangoni convection arising in a solutionpresenting a thermal gradient [6,8–9]. After completeevaporation of both solvent and water in few minutes, aporous polymer film with organized pattern of holes inthe micron range is recovered over a cm2 surface (Fig. 1).

The choice of the solvent is driven by the combinationof the following features: high vapor pressure, low boilingpoint, low solubility in water and preferentially higherdensity than water. The data of different solvents reportedin Table 1 highlight why carbon disulfide and chloroformare the best candidates for the formation of highlystructured honeycomb polymer films prepared by the fast

mer films prepared by the breath figure method.

Table 1Data for different solvents [30].

Chloroform Dichloromethane Carbon disulfide Toluene Tetrahydrofuran Pentane Diethylether

Ethylacetate

Density (g/cm3) 1.48 1.32 1.26 0.86 0.89 0.62 0.71 0.90Vapor pressure (KPa) 21.3 46.5 39.7 2.9 21.6 56.8 58.6 9.7Solubility in water (g/L) 8.2 20 2.9 0.5 Miscible 0.4 69 87Boiling point (�C) 61 39 46 110 65 36 34 77

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evaporation method with water condensation (breath fig-ure method). The simplicity of the BF pattern formationhas led to the preparation of ordered porous films usinga wide variety of polymers and different macromoleculararchitectures (linear, star, graft, dendritic, hyperbranchedpolymers and coil–coil or rod–coil diblock copolymers)during the last years [1–3,7,10–29].

In 2006, Bunz et al. [2] and Stenzel et al. [3] publishedtwo reviews on the formation of honeycomb structuredpolymer films via breath figure templating. They presentedthe mechanism of honeycomb polymer film formationthrough the fast solvent evaporation method under humidatmosphere and provided an overview of the parametersinfluencing the surface structuration. For instance, Stenzelet al. [3] detailed the influence of the casting conditions(relative humidity (RH), airflow, concentration) on boththe quality of ordering and the pore size. Both reviewssummarized the different nature of the polymers or mix-tures of polymers and nanoparticles which were good can-didates for honeycomb film formation. The very recentreview published by Hernández-Guerrero and Stenzel[31] has confirmed the continuous interest in honeycombpolymer films structured by BF method since 2006.

The aim of the present review is first to summarize theadvances in breath figure templated porous polymer filmsthrough the recent articles exploring the architectures andmicrostructures of polymers together with investigation ofhoneycomb film formation (role of interfacial tension,influence of experimental parameters, substrate, dynam-ics . . .). Second, we have chosen to discuss the recent liter-ature that focuses on the following aspects: hierarchicallystructured polymer films obtained by BF method; hybridhoneycomb polymer films prepared by either self-assem-bly of hybrid nanoparticles or growth of inorganic materi-als from precursor of nanoparticles or directly from the HCfilm; fluorescence in HC films; biomaterials based on HCpolymer films (organized porous polymer films decoratedwith glycopolymers and/or sensing of biomolecules) andfunctional HC films including smart surfaces responsiveto external stimuli and superhydrophobic surfaces.

2. Formation of honeycomb patterned polymer films

2.1. Influence of polymer architecture and/or microstructure

The effect of architecture and microstructure of poly-mer on the formation of regular arrays of pores in the poly-mer films prepared by BF approach has been extensivelyreviewed in 2006 [2–3]. For instance, Stenzel and co-work-ers investigated the effect of the number of branches/arms,the length of branch/arm and the polymer molar mass of

star and comb polymers on the honeycomb film features[3]. It was concluded that although there is no prerequisitefor the polymer architecture, complex structures toleratemore variability in casting conditions. Indeed, starpoly(D,L-lactide), star polystyrene and hyperbranched poly-styrene showed the ability to self-assemble onto highlystructured honeycomb films [1,7,20,32] whereas linearhydrophobic polymer did not lead to regular films whencast under similar conditions [3,15]. Regular films couldbe generated from linear polystyrene of high molar mass(Mn > 100,000 g mol�1) when containing carboxylic acidterminal group [13] or without any polar group only ifthe casting conditions with different solvent were finelytuned [33]. More recently, Billon and co-workers obtainedhighly ordered honeycomb films based on linear polysty-renes of low molar mass (Mn � 20,000 g mol�1) with ionicchain end (called ionomer) [22,34]. They took advantageof the self-assembling of these ionomers into inverse mi-celles in the organic solvent to produce in situ star-likepolymeric structures. Moreover, it seemed that ionomersprevented water droplets coalescence and led to very reg-ular pore size, probably due to the stabilizing properties ofthe PS-COO�Na+ at the water/carbon disulfide (CS2) inter-face [22]. The ionic terminated PS were synthesized inone-step simple reaction by nitroxide-mediated polymeri-zation using either a bicomponent initiating system with acationic initiator and the SG1 nitroxide as control agent[34] or a carboxylic acid based alkoxyamine [22]. It wasalso mentioned in early literature [7] and recently [35] thatself-assembly of rod–coil diblock copolymers into micellesin a selective solvent of one block promoted the formationof ordered pore assembly. Nevertheless, coil–coil hydro-phobic diblock copolymers entirely soluble in the solventbut self-assembling into nanophase segregation of theimmiscible blocks, also produced highly ordered HC film[24]. It is worth to note that in the case of amphiphilic di-block copolymers, the self-assembly into inverse micellesinduced a second non-controlled porosity [18,27].

Since 2005, Qiao and co-workers have focused theirinterest on the synthesis of a library of core cross-linkedstar (CCS) polymers for the production of honeycomb films[36–38]. The CCS polymers were synthesized by ‘‘arm first’’strategy using atom transfer radical polymerization[39–41]. The effect of glass transition temperature (Tg) ofdifferent CCS polymers (poly(dimethylsiloxane) PDMS,poly(ethyl acrylate), poly(methyl acrylate), poly(tert-butylacrylate), poly(methyl methacrylate)) on the self-assemblyof HC films on non-planar substrates was studied [38]. It isinteresting to note that all star polymers self-assembledinto organized structured films by BF method whereasnone of the original linear precursors with low Tg were able

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to form stable ordered porous films [38]. Moreover, thefilms cast from the low Tg star polymers showed morehomogeneous films with much less cracking throughoutthe film in comparison with high Tg star polymer [38,40].The poly(dimethylsiloxane) CCS were suitable to form HCfilms onto inorganic particles based surfaces including sil-ica, glass micro-beads, kaolin, sodium chloride and sugarcrystals [42]. Core-cross-linked core-shell nanoparticleswere also obtained by self-assembly of PS-b-P(S-alt-MAh)-b-PS triblock copolymers and subsequent cross-link-ing of the core via the maleic anhydride units (MAh) and adiamine. The core-corona ratio determined the size of thepores and the regularity of the pore arrays of the porousfilm [43].

The improvement of the HC film properties and stabilityis a crucial point for their use in different environments.For that purpose, several groups have recently attemptedto cross-link the polymer inside the HC film by differentchemical pathways [20,35,44–50]. A simple photochemicalcross-linking by UV irradiation was performed either in thepresence of air for polystyrene [48] and poly(vinyl cinna-mate) [50] based HC films or under nitrogen for poly(1,2-butadiene) HC films [49]. The preparation of anazide-substituted poly(para-phenyleneethynylene) (PPE)was reported to cross-link the honeycomb film upon heat-ing at 300 �C [44]. Long et al. [20] generated cross-linkedordered microporous surfaces from well-defined four-arm star-shaped poly(D,L-lactide) end-modified with 2-iso-cyanatoethyl methacrylate. The 2,2-dimethyl-2-phenolacetophenone photoinitiator was added in the polymersolution prior the film formation and the films were subse-quently photo-cross-linked by UV irradiation. Star polysty-rene-b-polybutadiene honeycomb films were self-cross-linked by exposing to UV light in air at 30 �C for severalhours [35]. Karthaus et al. [45] achieved the preparationof thermally stable and solvent resistant honeycomb filmsby immersing a poly(styrene-co-maleic anhydride) basedHC film in an ethanol solution of a, x alkyldiamine to pro-mote the chemical reaction. In this example, a polyioncomplex was added as an additive (5–10 wt% vs. polymer)to ensure the formation of the hexagonal array by reducingthe surface tension of the water droplets. The same proce-dure was repeated by Stenzel et al. to form stable cross-linked honeycomb films for the further attachment of aRAFT agent allowing the surface initiated polymerizationof N-isopropylacrylamide and N-acryloyl glucosaminemonomer from the structured film [46]. A recent article re-ferred to the synthesis of methacrylic branched copoly-mers containing an alkoxysilane-based co-monomer topromote the film cross-linking via the sol–gel processusing triethylamine acetonitrile/water solution as catalyst[47]. The cross-linking step improved the flexibility, theresistance to organic solvent (chloroform) and thermal sta-bility up to 85 �C. Li et al. used commercially availablepolystyrene-b-polyisoprene-b-polystyrene triblock copoly-mer and polystyrene-b-polybutadiene-b-polystyrene withhydroxyl groups to elaborate micropatterned polymersthrough the BF method [51–52]. Self-supported three-dimensional structures with enhanced thermal stabilityand solvent resistance were obtained by a vulcanizationof the honeycomb structured polymer film using S2Cl2

molecules absorbed into polymer films by vapor phasetransfer for 4 h [51–52]. Finally, non soluble ordered poly-meric pattern of polyfluorene copolymer was obtainedafter a thermal treatment of the polyfluorene containingtetrahydropyranyl residues as protecting groups of the sidechains [53]. In that case, the retention of the structure afterannealing at 230 �C was possible only by preventing thecollapse of the cavity walls by covering the HC film with li-quid polydimethylsiloxane mixed with curing agent [53].Another way to fabricate thermally stable honeycomb-pat-terned film by the BF method was to use a solution of ther-mally stable polymer such as for instance polyetherketonecardo (PEK-C, glass transition temperature of 230 �C) [54]or hyperbranched poly(phenylene vinylene) [55]. The lasthexagonal porous film is very thermally stable and re-tained its structure at up to 600 �C. After heating to600 �C at a rate of 10 �C/min under a nitrogen atmosphere,carbonization of hyperbranched poly(phenylene vinylene)occurred and black porous carbon film was obtained [55].

2.2. HC film structure

The parameters influencing the film formation weresummarized by Bunz et al. [2] and Stenzel et al. [3]. Itwas concluded from the literature that one of the criticalsteps in the formation of ordered porous polymer filmsby the BF method was the polymer precipitation at thesolution/water interface. This was early investigated byFrançois et al. [56] who showed that star-polystyrene pro-moted the formation of a thin polymer layer encapsulatingthe water droplet, hence preventing the droplet coales-cence. Since five years, studies have been regularly pub-lished on the honeycomb film formation with a focus ondifferent issues: the role of interfacial tension and solvent[13,57–60], the influence of the experimental parameters(temperature, polymer concentration, humidity, solvent,evaporation time, substrate . . .) [28,32,34–35,38,61–63],the study of dynamics [64–67] and characterization ofthe film ordering [68].

Along with superficial patterns, multilayer structureswith a regular arrangement of pores can be obtained viaBF templating. A first report related the presence of poremultilayer to the lower density of the water-immisciblesolvent (toluene, benzene) in comparison with water den-sity as 3D pattern pores was assigned to successive sinkingof condensed water droplets into the polymer solution [8].However, multilayer structures have also been observedfrom solvent exhibiting a higher density than water (car-bon disulfide and chloroform) [1,11,22,57,69]. Bolognesiet al. [13] proposed a prediction model showing that theformation of mono- or multilayer structures can be tunedby the interfacial energy between solvent and water. Thevalue of z0 is detailed by z0 = (cW � cW/S)/cS with cS andcW the surface tensions of solution and water, respectively,while cW/S is the interfacial tension between water and thesolution. It was established that for z0 value between �1and 1, the drop is floating at the interface between airand solution, which indicates a monolayer of pores. Forz0 greater than 1, drops swell below the surface and multi-layer structured films can be obtained. It should be notedthat z0 values for the polymer solutions cannot be

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1005

calculated in detail because the full set of c is not available.The data of the pure solvent were used and values of z0

were estimated in different solvents: z0 � 0.8 for CS2/waterproviding monolayer structures, z0 � 1.3 for toluene (orbenzene)/water providing multilayer structures [13]. It isworthwhile to remark that during carbon disulfide evapo-ration, the solution concentration raises and then cH2O=CS2

decreases. This means that during film formation waterdroplets may continuously penetrate inside the solutionuntil motion freezing and film hardening. This phenome-non might explain that the model cannot systematicallypredict the experimental observations. Dong et al. [57] re-cently investigated the dimensional architecture of ferr-ocenyl-based oligomer honeycomb-patterned films. Fromtheir polymer/CS2 mixed solutions, they observed singlelayer near the edge but two and three layers were presentapproaching the center of the film. The solvent undeniablyplays a role in tuning the morphology of the HC film butbesides the solvent, the final pore structure is regulatedby kinetics through the effect of the polymer concentration[11,59], solution viscosity (driven by molar mass and con-centration of the polymer) [33] and film thickness[22,37,55]. Servoli et al. [59] compared the theoretical pre-dictions of the model based on interfacial interactions withtheir experimental data for poly(D,L-lactide) honeycombfilms prepared from two different solvents (z0 values of1.6 and 1.9 for chloroform and ethyl acetate, respectively).The data suggested that interfacial interaction alone can-not explain the formation of either multilayer pore struc-ture or single layer when using the same polymer/solventmixture but varying the processing experimental condi-tions [59]. When solvents with proper interfacial proper-ties are subjected to slow evaporation, BF films with poremultilayers were obtained whereas just a monolayer is ob-served for fast evaporation despite favorable water/solventinterfacial tension [59]. For honeycomb-pattern filmsbased on linear polylactide (PLA), it was reported that diol-eoylphosphatidylethanolamine (DOPE) was the most suit-able surfactant among various kinds of phospholipids. Inorder to elucidate the effectiveness of DOPE in the forma-tion of honeycomb-patterned PLA films, the interfacial ten-sion between the water droplets and polymer solution wasinvestigated by Fukuhira et al. [58]. They conducted a thor-ough study by measuring the interfacial tension at foursimulated stages of evaporation using four concentrationsof polymer solution between 5 mg/mL and 100 mg/mL ofPLA in chloroform for six phospholipid surfactants withdifferent hydrophile–lipophile balance (6.5 < HLB < 9.1)[58]. It was shown that DOPE having the lowest HLB(6.5) exhibited the highest interfacial tension above15 mN/m and that the interfacial tension of each surfactantdecreased with increasing concentration. The polymersolution concentration, calculated from the polymer solu-tion weight taken every 30 s during the solvent evapora-tion, was correlated to the optical interference of theregularly formed array observed every 60 s. The interfacialtension being previously estimated for different concentra-tions, it was concluded that the DOPE surfactant was effec-tive surfactant to form ordered array because the DOPEwas able to maintain high interfacial tension (>10 mN/m)during film formation [58]. The same research group also

discussed the relation between uniformity of the polysty-rene microporous films and interfacial tensions betweenwater and chloroform solutions of poly(N-dodecylacryla-mide)-co-poly(6-acrylamidohexanoic acid) amphiphiliccopolymers [70]. For interfacial tensions above 10 mN/m,both the size of the polymer frame (wall thickness) andthe standards deviation decreased with a decrease of theinterfacial tension [70]. Harkins et al. [71] expresses thespreading coefficient (S) as follows: S = cP � (cW + cW/P),where cP is the surface tension of the polymer solution,cW is the surface tension of the water droplet, and cW/P isthe interfacial tension between the polymer solution andthe water droplets in this case. This means that an increaseof cW/P diminishes the spreading coefficient and the drop-let maintains a globular shape. Saunders et al. [60] alsoshowed that the interfacial tension between polymer solu-tion and water was a key parameter in the pore size andordering quality. Breath figure templated poly(ethyleneoxide)-b-poly(fluorooctyl methacrylate) (PEO-b-PFOMA)block copolymer films were obtained by casting 1,1,2-tri-chlorotrifluoroethane solution under humid atmosphere.Four polymers were studied with a similar molar mass ofthe PEO block (2 kg mol�1) and different molar masses ofthe PFOMA block (Mn = 10, 25, 70, 140 kg mol�1). Changein the viscosity alone cannot explain the structure of theporous films as the usual trend was not observed: thelow Mn polymers exhibited lower pore sizes than the high-er Mn polymers and the very large fluorinated blockcopolymer (Mn = 140 kg mol�1) significantly inhibitedwater droplet nucleation and organization due to the re-duced water wettability at the air/solvent interface [60].The optimal film organization was observed for the PEO-b-PFOMA (2–70 kg mol�1) exhibiting an interfacial tensionof 22 mN/m [60].

The influence of polymer concentration, relativehumidity, solvent properties and substrate on the patternformation has been widely investigated in many studiesas these crucial parameters have to be optimized for newpolymer–solvent mixture. The general trend of eachparameter effect was summarized by Stenzel et al. [3]and the recent published examples listed below confirmthis trend. Indeed, the increase of the concentration ofpolymer solution systematically led to lower pore diame-ter [32,35,54–55,63] and an optimum concentration wasrequired to target pore ordering (star polystyrene-b-poly-butadiene [35], poly(lactide-co-glycolide) [61]). The vis-cosity of the solution increases with polymerconcentration resulting in the slower growth of droplets,a faster polymer precipitation at the water droplet inter-face and lower pore size. Wu et al. [61] tuned the experi-mental parameters (polymer concentration, solvent,humidity, co-monomer ratio) to elaborate poly(lactide-co-glycolide) honeycomb films without inclusion of surfac-tant which had been previously considered as essential toobtain ordered poly(lactide)-based porous films [72–73].The relative humidity is also a determining parameter forthe size of the micropores where pore size increases withincreasing humidity [25,61,63]. The relative humidity isusually controlled by adjusting the air flow rate. Higherhumidity not only forms larger water droplets but alsoslows the solvent evaporation, both of which lead to the

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growth of droplets and the formation of larger pores. Theeffect of evaporation time was evidenced by Dong et al.[32] by varying the casting volume of poly(3-ethyl-3-oxe-tanemethanol)-star-polystyrene/chloroform solutions. Theincrease of the casting volume induced an increase of theaverage pore diameters. Jiang et al. [28] reported the prep-aration of honeycomb microporous films from a solublefluorinated poly(siloxane imide) segmented copolymer.The results showed that among different chlorinated sol-vents, only chloroform could form regular porous filmswith pore shape and size varying with relative humidity[28]. Tian et al. [74] suggested that the formation of hon-eycomb structures depends on the thermodynamic affinitybetween polymer and solvent. They investigated thebehavior of polyphenylene oxide in various solvents andconcluded that the thin polymer film formed on the sur-face of water droplets was formed only for good solvents[74]. Indeed, when a poor solvent was used, migration ofpolymer chains to the water/solution interface was re-stricted, resulting in coalescence of water droplets andpoor ordering of pores or no BFs [74]. Two studies of Penget al. [33] and Ferrari et al. [62] showed that for linearpolystyrenes of molar mass above 192,000 g mol�1 with-out any polar end group, well-organized porous structureswere formed in chloroform. For carbon disulfide solutionsof non polar high molar mass polystyrene cast onto glasssubstrate, Ferrari et al. [62] and Li et al. [48] preparedhighly ordered HC films under a static BF process whereasPeng et al. [33] did not observed the formation of orderedarray under dynamic condition (humid air flow). As de-picted in Table 1, the low boiling point and the high vaporpressure of CS2 favors the fast solidification but it cannotalone explain the results of Ferrari et al. [62]. Indeed, chlo-roform was a more suitable solvent than CS2 when poly-mer solution was cast onto hydrophilic glass (glasstreated with sulfuric acid solution) but opposite resultwas obtained with untreated glass substrate. The contribu-tion of the nature of the substrate has not been clearly elu-cidated yet. The influence of the substrate on the BFpatterned films has been the object of few studies. Thegeneration of ordered porous polymer structures by theBF method, commonly processed onto glass, has also beenattempted onto different substrates including hydrophilic,silanized or fluorinated glass [62], mica [34,63], polymericsupports (polyvinylchloride (PVC) [34,62], polyethylene(PE) [62], polyethylene terephtalate (PET) [62]), non-pla-nar grids [38], silicon wafer [57,62–63], micropipette withcurvature gradient [75]. Billon and co-workers [34] ob-served a better organization of monodisperse pores of4 lm when the polymer solution was deposited onto afreshly cleaved hydrophilic mica surface in comparisonwith a less ordered structure and greater dispersity of poresizes for the HC film prepared on glass substrate. In thisstudy, PVC sheets were also used for the first time as flex-ible organic substrate and hexagonal array over a long-range order (few hundred microns) with lower pore sizediameter (1.5 lm) was observed by microscopy. The possi-ble interaction between the polymer with a cationic chainend and the negatively charged surface of the mica, whichmight have explained the difference of ordering betweenmica and glass substrates, cannot be applied to the PVC

substrate [34]. The influence of the substrate on the poreordering is not easily interpreted as a thin continuouspolymer layer is always formed at the bottom of the film.Ferrari et al. [62] showed the important role of the sub-strate (organic or inorganic) by preparing HC films by BFmethod from linear PS of 192,000 g mol�1 using three dif-ferent solvents (carbon disulfide, chloroform, dichloro-methane) for each substrate: glass submitted to differenttreatments (piranha solution (hydrophilic glass) and silan-ization with either 3-glycidoxypropyl methacrylate oroctyltriethoxysilane), silicon wafer, PE, PET, PVC. Whilecarbon disulfide was the only solvent able to form orderedBFs onto glass substrate, the same solvent was unsuitable(poor ordering or no BFs) for silicon wafer and treatedglass substrates submitted to treatments producing differ-ent surface chemistries. Carbon disulfide provided orderedBFs onto PVC but no hexagonal ordering was observedwith PET and PE using the same solvent. On the otherhand, the substrates exhibiting no ordering with carbondisulfide showed a well-organized pattern of pores withchloroform (PET, hydrophilic glass, silicon wafer and silan-ized glass). These experimental observations underlinedan interaction between solvent and support; chloroformappeared to be the most robust solvent less affected bythe change of the substrate [62]. From a qualitative view-point, Ferrari et al. [62] proposed that substrates with highsurface energy promoted the ordering of the PS/chloro-form solution while the ordering of PS/carbon disulfidesolution was mostly observed for substrates exhibitinglow surface energy. Several authors [63,76–77] have sug-gested that the wettability of the solid substrate with thepolymer solution plays an important role with a beneficialimpact of a high wettability on the periodicity and order-ing of the pores. Using glass micropipettes, Jiang et al.[75] investigated the effect of curvature on the formationof poly(L-lactic acid) (PLLA) honeycomb films. Scanningelectron microscopy images were taken at different crosssections characteristic of different surface curvature(k = 1/R with R the radius of the cross section disk). Themorphology of the PLLA honeycomb film changed at dif-ferent sections with both disordering and distortion ofthe pores with increasing curvature.

The film formation by BF method is controlled by boththermodynamic (stabilization of water droplets) andkinetic as the process is driven by a rapid solvent evapora-tion [67]. Since the early work of Shimomura and co-work-ers [67] who studied the dynamic of film formation via adual observation of the film (optical microscopy anddiffraction pattern) during solvent evaporation, recentstudies [64–66] have focused their interest on the dynam-ics of polymer breath figures. For linear PS/carbon disulfidesolution drop cast onto glass substrate, a drastic decreaseof the solution level height together with a decrease ofthe temperature between 0 and 100 seconds was observed[64]. In situ observation of growth and rearrangement ofwater droplets between 0 and 180 s was performed byoptical microscopy from a polyphenylene oxide/chloro-form solution [65]. The authors showed a first «bursting ef-fect» explained by the water droplets formation in a toplayer in the absence of evaporation due to the low solutiontemperature coming from the very fast solvent evaporation

Fig. 2. Top: graph of the diameter and speed of surface holes versus time. The squares indicate the speed, and the circles indicate the diameter. Below:schematic diagram of the mechanism for the BF process [65].

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(<70 s). Surface holes appeared by droplet burst of the thinpolymer layer encapsulating the droplets [65]. The ‘‘burst-ing hypothesis’’ was directly supported by the appearanceand movement of surface holes and indirectly supportedby the inner structure of the film. The BF process afterappearance of holes (72 s) was divided in three stages asdepicted in Fig. 2 [65].

A polymer nanocomposite film of polystyrene and goldnanoparticles was obtained by interrupting the condensa-tion of breath figures [66]. The different regions of theunfinished honeycomb structure were analyzed by opticalmicroscopy to probe the film formation dynamics. Thisstudy confirmed that the condensed water droplets growduring their arrangement on the nanocomposite film [66].Srinivasarao and co-workers [68] used optical microscopyequipped with a fast camera and Fraunhofer diffraction toobserve the HC films during formation, respectively in thedirect and reciprocal spaces. The use of a Voronoi ap-proach and the bond-orientational correlation function al-lowed for a quantitative characterization of the degree ofthe ordering of the structured microporous films.

3. Hierarchical structures in polymer films using breathfigure method

Hierarchically ordered polymeric films obtained by thebreath figure process exhibit an array of pores with sizeranging between 500 nm and 2 lm. Several groups havebeen interested in the introduction of a second structur-ation built at different levels. Two types of materials werestudied: the first one consists of films showing a substruc-ture at the nanometer length scale, the second consists offilms presenting a superstructure, typically at the lengthscale of few tens micrometers.

3.1. HC and substructure

It was demonstrated that the breath figure method canbe employed to prepare hierarchical morphologies pre-senting substructures achieved via the self-assembly ofblock copolymers. In the literature, among the papers pre-senting studies on HC films made of block copolymers only

Fig. 3. AFM phase images of PS-b-P4VP honeycomb film recorded in topographic mode (A) and phase mode (B) from reference [78].

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few explicitly showed a substructure. The first report onsuch material was published by Hayakawa et al. [11]. Thispaper showed the possibility to prepare hierarchically or-dered HC films made of semi rod–coil diblock copolymer:a polystyrene block and a polyisoprene block decoratedwith side chains of oligothiophene. A unique materialrevealing three levels of ordering was synthesized. Indeed,in between the honeycomb pores, the macromoleculararchitecture of the polymer conducted to a smectic order-ing of the oligothiophene rods within the polyisoprenecylindrical aggregates, themselves ordered inside the poly-styrene matrix [11].

More recently, it was shown that regular coil–coil di-block copolymers can be considered for preparing well or-dered honeycomb porosity with a concomitant copolymerself-assembly. Escalé et al. published two articles [24,78]reporting coil–coil diblock copolymer nanosegregation inbetween the hexagonally ordered pores of HC film, despitethe rapid BF process which is not favorable to reach thethermodynamical equilibrium for nanophase segregation.In the first article [24], four high molar mass diblockcopolymers based on styrene and n-butyl acrylate (PnBA-b-PS) or tertio-butyl acrylate (PtBA-b-PS) were synthesizedby nitroxide-mediated polymerization targeting differentmonomer weight fractions in order to obtain the lamellarand cylindrical morphologies. It was pointed out that boththe micrometric pore organization in HC film and the inter-nal nanometer length scale morphology of the diblockcopolymer self-assembly were affected by the copolymerfeatures, i.e. interaction parameter, glass transition tem-perature and monomer weight fraction [24]. In the secondarticle, Escalé et al. [78] demonstrated that hierarchicallystructured porous polymer films can also be elaboratedfrom the polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP)diblock copolymer (Fig. 3). The advantage of the P4VPblock was to induce a pH sensitive character to the finalmaterial. Indeed, after the film formation the hexagonallyordered P4VP cylinders can be turned to hydrophobic orhydrophilic as a function of the pH (pKa (P4VP) = 5.2).The reversible pH-responsive wettability of the film

surface was pointed out by contact angle measurementsat pH below and above the P4VP pKa, leading to, respec-tively, hydrophilic and hydrophobic characters. An in-crease of the surface roughness was obtained by peelingoff the top surface of the films, which led to an exacerba-tion of the hydrophobic and hydrophilic character at pH9 and pH 3, respectively (see Section 7.1). This work pre-sented the first report on honeycomb porous and pillardedfilms exhibiting a reversible pH-responsive character [78].

The use of amphiphilic copolymers was also exploredin order to localize and orient the polymer self-assem-bly, at the micrometer length scale, thanks to thepresence of the water droplets during the breath figureprocess. Munoz-Bonilla et al. [79–80] proposed studiesusing blends of polystyrene homopolymer andpoly(2,3,4,5,6-pentafluorostyrene)-b-polystyrene-b-poly-(poly(ethylene glycol) methyl ether methacrylate) amphi-philic triblock copolymer to produce a dual structure. Themicrometer size cavities were generated without orderingvia the BF process during polymer solution spin casting.The originality of this work resides in the fact that thetriblock copolymers were located preferentially in thecavities (at the interface with the former water droplet)inducing a nano structuration in the cavities only. Fur-thermore, the authors demonstrated that the localizednano-phase segregation presented a transition from mi-celles to lamellae when performing a thermo or THF va-por annealing [79–80]. In addition, the film exhibitedanother structural transition at the micrometer lengthscale, the cavities turn to ‘islands’ when performingannealing under wet condition. The initial porous struc-ture can be recovered by performing an annealing underdry condition.

3.2. HC and superstructure

In the literature, various methods were employed toachieve HC morphology together with an ordered super-structure. A top-down approach was associated with thebottom-up breath figure method by using for instance

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the periodic arrangement of TEM grids as substrate [36,38]or masks [81]. Connal et al. presented a pioneer work inthis area using TEM grid as substrate on top of which theydeposited poly(dimethylsiloxane) (PDMS) core cross-linked star polymer solutions to later form the HC mor-phology by BF method [36]. The authors assumed thatthe polymer Tg was crucial for the film flowing the non-planar substrate. In a second paper, Connal et al. confirmedthe effect of Tg since only polymers exhibiting a Tg below50 �C were able to fit the TEM grid morphology [38]. Theaim of these studies was to show the feasibility of coatingcurved surfaces with a layer of HC polymer film for futureapplications on micro-fluidic channels. Another objectivewas to use the hierarchically ordered films as mold forsoft-lithography to prepare cross-linked PDMS stamps.The same group proposed a second method to get discreteislands of HC, dipping the grid in the polymer solution be-fore HC film formation, the solution is then retained by thecapillary forces in the mesh of the grid where the HC willbe localized [36]. This idea of PDMS molded stamps waspursued by Galleoti et al. using a TEM grid on top of aHC film, such a mask, before the molding procedure [81].More recently, Gong et al. [82] have used TEM grids to pre-pare a two-level microporous hybrid film from polysty-rene-b-poly(acrylic acid)/ferrocene solution. The texturedsurfaces were used as templates to grow the multi-levelCNT patterns, e.g. isolated and honeycomb-structuredCNT bundle arrays perpendicular to the substrate. Masksfor UV photolithography on a HC film made of UV photo-polymerizable molecules [83], UV cross-linkable polymers[49] or on polymer presenting a solubility transition whenexposed to UV [84] were also used to prepare hierarchi-cally ordered films. Kim et al. [83] presented a studyemploying amphiphilic molecules made of benzamidedendron and an aliphatic dendron containing two diaceth-ylene groups. UV photolithography was used to inducelocalized cross-linking between the diacetylenes that arephotopolymerizable to form polydiacetylenes. After wash-ing the films in solvent, only the cross-linked domains re-mained and patterned honeycomb lines with widths of fewmicrometers were revealed. The minimum width achievedwas in the order of the pore dimension. Kojima et al. [84]prepared HC films with a photo-responsive amphiphiliccopolymer containing photochromic spiropyran. Spiropy-ran is a hydrophobic photochromic compound which isphotoisomerized to zwitterionic merocyanine by UV lightirradiation. The merocyanine area formed with UV irradia-tion using masks retained its honeycomb-pattern against

Fig. 4. Diverse hierarchical porous structures induced by various shapes of gratigrating. (b) SEM images of ordered structures fabricated using a parallel grating

chloroform vapor, whereas the spiropyran area was dis-solved. With this method no particular orientation of theHC ordering was obtained.

Perfect control and orientation of the HC structure canbe achieved using the method proposed by Park et al.depositing a template on top of the evaporating solutionbefore the formation and self-organization of the waterdroplets leading to hexagonally packed arrays holes inthe mesh space of the grating (Fig. 4) [85]. This methodled to periodic structures at the length scale of few tensmicrometers concomitantly to a well-controlled HC struc-ture. Most interestingly the authors showed that the shapeof the gratings played a role on the quality of orientation ofthe HC through the physical confinement. Indeed, the hex-agonal grating induced a perfect hierarchical structure,since the grating shared all the principal axes with the hex-agonal array of pores. The parallel bar grating induced ahighly ordered two-dimensional structure with pores line-arly organized along the edge of the grating (Fig. 4b). Final-ly the square grating presented an improved degree ofordering despite the inconsistency between the gratingand the pore array axes (Fig. 4c). Furthermore, the authorsdiscussed the effect of the amount of surfactant in thepolymer solution on the quality of the HC structure atthe interface between the polymer and the grating. Theyshowed that increasing the concentration of surfactant im-proved the degree of ordering of the HC thanks to a betterwettability of the polymer on the grating [85].

4. Highly structured hybrid honeycomb polymer films

The concept of using materials of different chemicalnatures and assembling them to obtain a new one thatexhibits enhanced properties can be applied to many dif-ferent fields. Although, to obtain interesting properties, asimple mixture of organic and inorganic materials is notenough, one has to organize them in a specific way. Someof the most significant examples of such hybrid systemscan be found in nature with diatoms especially [86–88].For instance, bio-mineralization could be described as theprocess by which living organisms assemble solid nano-structures from occurring inorganic and organic com-pounds. The resulting organism could actually bedescribed as ‘biohybrid’ in which biomolecules and inor-ganic components are intimately associated. The enhancedproperties of these hybrid materials are not only a result ofthe combination of the intrinsic properties of both

ngs. (a) SEM image of hierarchical structure fabricated using a hexagonaland (c) a square grating from reference [85]).

Fig. 5. (Left) Confocal images of BF formation on PF8BT (top) and self-assembled OxZLCOOH at the polymer–air interface in the cavities of a BF PF8BT(bottom). Yellow and Red fluorescence are due to PF8BT and OxZLCOOH, respectively [90]. (Right) TEM images of cross-sections through the porouspolystyrene film. Overview of micron-sized holes (top) and magnification of the polymer–air interface, where the CdSe nanoparticles can be seen as a thinblack layer (arrowed) (bottom). The inset shows another spot at the polymer–air interface inside one of the holes [91].

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materials, but the dimensions and arrangements of the dif-ferent species are also key factors. Only few examples ofstructured hybrid films using low cost preparation meth-ods especially by a bottom-up approach, as the BF process,have been described. In the following part, we will describethe elaboration of hybrid HC polymer films through eithera simultaneous self-assembly of polymer and hybrid nano-particles or by the in situ formation of hybrid particles fromprecursor or by using HC film as a template. We willmainly pay attention to the recent studies published since2006 as previous works were reviewed by Bunz [2].

4.1. Self-assembly of polymer/nanoparticle blends

The combination of two self-assembly processes onmultiple length scales leads to the formation of hierarchi-cally structured hybrid honeycomb. In this idea, theformation of HC by BF method can be combined with theself-assembly of polymer/nanoparticles mixture at thepolymer solution–water droplet interface. This polymer/NPs blend-assisted fabrication is a procedure combiningthe so-called ‘‘pickering emulsion’’ and BF processes. Thecomplete evaporation of the solvent and water confinesthe polymer/particle blend assembly into the walls of anarray of micron-sized spherical cavities.

Hult and co-workers [89] used this approach to forcethe self-assembly of poly(9,90-dihexyl-fluorene) (PDHF) inpresence of polystyrene-grafted silica nanoparticles(Si-graft-PS). Blends of Si-graft-PS with 10–60 wt% of PDHFwere dissolved in CS2 and drop cast onto a glass substrateunder humid conditions (66–85% humidity). Highly or-dered close-packed micro-porous films were obtained withan average pore size between 3.6 and 5.2 lm. A red shift in

emission from 420 to 449 nm was observed for continuousspin casted and honeycomb film formed with 60 wt% ofPDHF, respectively. The shift was attributed to theenhancement of the intermolecular interactions inducedby PDHF–water interactions during HC film formation. In-deed, because water is a poor solvent for PDHF, the aggre-gation of PDHF chains was then forced by theirconfinement into the walls. From this concept, it was alsopossible to force the localization of amphiphilic zeolitecrystals at the interface inside the pores. Vohra et al. [90]used a solution of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-(2,10,3)-thiadiazole)] (PF8BT) random copolymercontaining a carboxylic acid-functionalized oxonine-loadedzeolite crystals (OxZLCOOH) (5 wt% in respect to polymer).The confocal fluorescence microscopy clearly showed twodifferent emissions from the borders of the cavities andfrom the rest of the film (Fig. 5 left). The amphiphilic crys-tals moved toward the water droplet interface to stabilizeit, i.e. pickering emulsions. Using such a system, two levelsof organization were obtained: a regular hexagonal arrayof micro-cavities in a polymeric film and a selective posi-tioning of the zeolite in the polymeric micropatterned film[90]. Boker et al. [91] demonstrated that this process canlead to the decoration of the pores surface by cadmium sel-enide CdSe quantum dots (QD) of 4 nm diameter (Fig. 5right).

Since the first study of Boker et al., several other metal-lic nanoparticles such as Fe2O3 as super paramagnetic NPs[92–93], magnetic Fe3O4 NPs [93], gold (Au) [93–96] or sil-ver (Ag) [92,95] nanoparticles and CdSe/CdS QDs [93] havebeen used to create highly ordered hybrid honeycombfilms. The nanoparticles which are immiscible with thepolymer matrix showed interfacial activities driving the

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film formation by stabilizing the water droplets during theBF process. The self-organized macroporous honeycombfilms showed the combined properties of both the NPsand the ordered inverse opal structures. Such hybrid filmscould be used as new photonic band gap materials [93],light-emitting device [90] or magnetic patterned surfaces[92–93]. The introduction of functional nanoparticles intohoneycomb films provides a simple mean of fabricating in-verse opals with photoelectric properties that have poten-tial applications in optics and microelectronics [89].Moreover, the design of organic electronic devices as wellas photonic and bandgap materials can be achieved bymixing organic conductive NPs as CarbonNanoTubes CNT[95,97–98] or fullerene C60 [99] with conjugated poly-mers. Nurmawati et al. [97] used a semiconducting poly-mer based on an asymmetrically functionalizedPolyParaPhenylene, i.e. CnPPPOH, with incorporation of along alkyl chain (Cn) on one side and hydroxyl group onthe other side of the polymer backbone leading to the de-sired amphiphilicity. Microporous honeycomb patternedfilms were prepared by direct spreading and evaporationof dilute polymer/CNT chloroform solution (0.05 wt%).The polymeric film with blue-light-emitting properties ob-tained from C12PPPOH presented a highly periodic, defect-free structures with a good spatial distribution of CNTs[97]. This straightforward and inexpensive method forthe preparation of hybrid thin films has been extended tohomogenous distribution of gold and silver NPs presentingplasmonic properties. Synergistic self-organization ofmetallic NPs and semiconducting polymer resulted in effi-cient quenching of the hybrid films, demonstrating stronginteractions between NPs and C12PPPOH [95]. Such phe-nomenon has also been demonstrated with a blend ofC60 and PolyPhenyleneVinylene PPV (P1) [99]. Well-dispersed CNTs were also used for the preparation of asuperhydrophobic and conductive porous nanocompositecoating [98]. After casting the CNT/regioregular poly(3-hexylthiophene)-block-polystyrene rrP3HT-b-PS dispersionfollowed by rapid evaporation of the solvent, a superhy-drophobic surface (water contact angle � 154–160�) witha conductivity in the range of 30–100 S cm�1 was obtained.Nevertheless, some developments have still to be done tocreate highly structured superhydrophobic and conductivefilms. The recent study of Ji et al. was the only work pre-senting an elegant way to tune the localization of silicaNPs inside a highly structured honeycomb film dependingon the NP surface functionalization [100]. Using the parti-cle-assisted fabrication of honeycomb-structured hybridfilms, both hydrophilic and hydrophobic SiO2 NPs wereused to prepare HC films. It appeared that a honeycomb-patterned structure could be successfully formed regard-less of particle wettability. The hydrophilic raw nanoparti-cles were basically adsorbed on the pore surface whilehydrophobic octadecyltrimethoxysilane-modified particleswere assembled into the interior walls. Due to the hydro-philic nature of raw silica particles, they were mainly lo-cated in the water phase during the early stage of BFprocess. For the hydrophobic functionalized silica NPs,the precipitating polymer layer was pulled around thedroplet, hence forcing the hydrophobic NPs to be localizedinside the walls. Here, one can mention that highly ordered

honeycomb-structured gold NPs (stabilized by dodecane-thiol) films can be achieved without the use of polymers[101–102]. Moreover, Han et al. were able to finely tunethe shape of the pores, from spherical to elliptic pores, justby orienting the airflow across the solution surface [101].

4.2. In situ formation of the hybrid honeycomb films

Mixtures of polymer and metallic precursors of NPshave been used to create micro-patterned hybrid polymerfilms by BF method. The polymer governs the honeycombfilm formation with micron-sized pores and the walls arefilled with the precursors of NPs. Thus, highly structuredhybrid honeycomb polymer films can be created in situand in some cases, the polymer phase can be burned outby pyrolysis to form an entire inorganic HC film.

The polymer-nanoparticle composite film can also beprepared by a one-pot reduction of metallic ions duringthe film formation as described by Jiang et al. [103]. In thiswork, by in situ reduction method, the presence of silvernanoparticles (Ag NPs) in PolyUrethane (PU) influencedthe formation of regular pore arrays on the surfacedepending upon the humidity levels, the content of AgNPs and polymer. It was noticed that Ag NPs promotedBF formation at low humidity (<30% humidity). Chenet al. proposed an alternative strategy to fabricate func-tional honeycomb-patterned films with controllable poresizes via BF based on ionomers [104]. Ionomers are poly-mers with a small mole fraction of chemically bonded ionicmoieties. In this case, well-defined poly(methyl methacry-late)/cadmium acrylate (PMMA/Cd(AA)2) ionomers weresynthesized via radical polymerization and Cd(AA)2 (twoacrylates bonded to one Cd2+) acted as a cross-linker. Sub-sequently, ordered porous films were successfully depos-ited on glass substrates from the ionomer solutionsunder a humid environment. The pore sizes of these filmscould be simply tuned by adjusting the classical experi-mental parameters such as the concentrations of the iono-mer solutions or the molar ratios of monomers. Moreover,depending on the chemically bonded Cd2+ ions in the poly-mer matrixes, in situ generation of CdS NPs was possible byexposing the chloroform solution of PMMA/Cd(AA)2 to anH2S atmosphere. Evaporation of the solvent yielded to hon-eycomb-patterned PMMA/CdS QDs-polymer films whichshowed favorable fluorescence in the absence of quench-ing, characteristic of the good dispersion of the NPs inthe polymer film. Moreover, hydrophobicity was observedover several months. Li et al. [105] fabricated patternedcomposite film with hemispherical TiO2 microparticles ly-ing in the holes of a honeycomb polystyrene film. The TiCl4

precursor was located inside the condensed water dropletswhich acted as ‘‘microreactors’’ for the TiCl4 hydrolysisconcomitantly to the formation the ordered porous poly-mer matrix.

A second approach consisted in first using the honey-comb polymer films to localize the precursors inside thewalls and to further generate the growth of NPs after burn-ing the organic phase, thus creating honeycomb inorganicfilms. As mentioned previously, the deposition of ZnONPs precursor was achieved by Karthaus et al. using apoly(styrene-co-maleic anhydride) (PS-co-PMAh) to create

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a patterned zinc oxide (ZnO) containing polymer films byBF templating [106]. They also described the possibilityto create a pure ZnO honeycomb film with photocatalyticproperties. An amphiphilic polyion complex (PIC) was firstprepared by mixing equimolar amounts of an aqueoussolution of poly(styrene sodium sulfonate) (PSSNa) and avesicular emulsion of bishexadecyldimethyl ammoniumbromide. The polyion complex was further mixed with zinccomplex, i.e. acetylacetonate hexahydrate Zn(acac)2, invarious ratios. With the 1:1 mixture of Zn(acac)2:PIC,well-developed honeycomb films can be achieved but thestructure is destroyed upon pyrolysis because the amountof inorganic material was not enough to retain the orga-nized structure [106]. The 5:1 mixing ratio allowed toovercome this problem and produced stable honeycombstructures after pyrolysis. The pyrolysis obviously led toshrinkage of the film, but the integrity of the in-planestructure of the honeycomb film was well preserved. Theorganic material in the rim decomposed, and thus therim got thinner but the pore-pore distance remained sim-ilar. Moreover, fluorescent images of such films under vio-let excitation showed a weak blue fluorescence, whichpointed out a crystalline ZnO film with few defects. Thesame process was used by Zhao et al. to produce a honey-comb structured hybrid film into inorganic photoactivetitanium oxide TiO2 film [107]. A solution of PS(Mw = 30,000 g mol�1) with titanium tetraisopropoxide(TTIP) as TiO2 precursor was prepared. They demonstrateda simple and effective vapor phase hydrothermal modifica-tion method (calcinations at 550 �C for 2 h) capable oftransforming a 3D honeycomb structured PS/TTIP hybridfilm into a photoactive TiO2 film without dismantling theoriginally templated 3D structure. The preservation of theorganic/inorganic hybrid film structure during its conver-sion to pure inorganic film by means of pyrolysis was en-sured [107]. Ma et al. [108] also reported a similar facilemethodology to prepare highly ordered ceramic micropat-terns on solid substrates by pyrolyzing UV cross-linkedpolymer microporous films formed by a poly-dimethylsiloxane-b-polystyrene block copolymer and tet-rabutyl titanate Ti(OC4H9)4, as a functional precursor ofTiO2. Taking advantage of the compartmentalization ofthe NP precursors inside the walls of the honeycomb films,

Fig. 6. (Left) SEM image of hydrothermal ZnO nanorod arrays grown from Zn(accarrays grown from ferrous honeycomb structured pattern [109].

Li and co-workers proposed a very interesting way to cre-ate a hierarchical structured honeycomb hybrid films[109–110]. They used an amphiphilic diblock copolymer,polystyrene-b-poly(acrylic acid) (PS-b-PAA), synthesizedby atom transfer radical polymerization exhibiting molarmass of PS and PAA blocks of 9000 and 2500 g mol�1,respectively (dispersity = 1.07). A classical procedure wasused to prepare a honeycomb structured film from a PS-b-PAA solution in CS2, containing ferrocene or zinc acetylacetaonate (Zn(acct)2) as chemical precursors of CNTs orZnO NPs, respectively. This film formation was followedby a photochemical cross-linking of the copolymer underUV light. After 4 h of UV exposure, the cross-linked filmwas heated at 450 �C within 2 h and held for another 5 hunder air atmosphere. During the pyrolysis, the functionalprecursor turned into oxide and replaced the polymer skel-eton, leading to functional inorganic patterns. Indeed, suchfunctional inorganic honeycomb films were used to growCNTs or ZnO nanorods arrays from ferrocene (using acety-lene flow at 750 �C) and zinc precursors, respectively(Fig. 6) [109].

Ma et al. [110] also generated the growth of CNTs bun-dles by Chemical Vapor Deposition (CVD) from the centerof the pores of the honeycomb patterns. In this case, theCNTs were perpendicularly oriented from the surface.The growth mechanism of the isolated CNT bundles wasattributed to the selective interfacial aggregation of theferrocene onto the surface of the cavities via the ‘‘picker-ing-emulsion’’ effect. On the other hand, honeycomb-likeskeleton of the dense CNT arrays was developed from thecatalytically functionalized hexagonal edges [110].

4.3. Polymer honeycomb films as templates

A different method to produce micropatterned inor-ganic/organic structures is to use polymer honeycombstructured films as templates for the deposition of inor-ganic nanoparticles (NPs) onto the surface by dipping thefilm into colloidal solution or by vacuum deposition of avolatile metal oxide precursor. In both cases, the honey-comb film needs to be stable in the solvent of the NPs orat the temperatures reached during vacuum evaporation.

t)2 honeycomb structured pattern. (Right) SEM image of carbon nanotube

Fig. 7. Fluorescence microscopy image of a PS microporous film covered with QDs and AFM image of the same sample (inset) (a) and same film after 30 minthermal treatment at 150 �C (b) [112].

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1013

Wan and co-workers [111] described a facile approachfor a selective assembly of silica SiO2 NPs on patterned por-ous surfaces. The polystyrene-block-poly(N,N-dimethyl-aminoethyl methacrylate) (PS-b-PDMAEMA) amphiphilicblock copolymer was synthesized by ATRP and used forthe preparation of honeycomb-patterned porous films bythe breath figure method. Positively charged films werefabricated by direct casting of the quaternized copolymeror by surface quaternization. Then, the negatively chargedraw SiO2 NPs can selectively assemble onto the externalsurface or across all surfaces of the film by simple modula-tion of the hydrophilicity of the surface. Indeed, when anegatively charged poly(sodium acrylate) was adsorbedonto the external surface of the film, it could serve as aneffective blocking layer to drive the selective assembly ofNPs into the pores. Thus, the wettability and the Cassie–Wenzel transition were proved to be the key factor forthe selective NP assembly onto the highly porous films[111]. Using a similar approach, Galeotti et al. [112] cre-ated cadmium telluride (CdTe) nanocrystal assembliesguided by breath figure templates. The honeycomb filmswere prepared using a CS2 solution of a long chain polysty-rene (Mw = 230,000 g mol�1), which guaranteed therobustness of the structure, mixed with a short chain ami-no-terminated (Mw = 4700 g mol�1), which was requiredfor obtaining well-ordered BFs. The presence of a smallamount of the amphiphilic PS stabilized the water/CS2

interface during BF formation preventing the collapse ofwater droplets, as previously described [22,34]. Eventhough the internal surface of cavities was enriched withthe most polar groups of the polymer, i.e. amino groups,the top surface of the film was still too hydrophobic tobe wetted by water. The microporous PS films were thensubjected for 20 s to oxidative plasma treatment beforebeing dipped into the solution of CdTe quantum dots(QDs) stabilized by sodium mercaptopropylcarboxylate[112]. The hybrid film resulting from the deposition ofQD solution, when seen by the fluorescence microscope,was not much different from the pristine PS film exceptit was emitting in the red (Fig. 7a).

Such thin layers were then subjected to a thermal treat-ment above the Tg of both polymers (150 �C for 30 min).While the BF structure of raw PS film completely collapsedduring the treatment, the HC film covered with QDs re-tained its organized structure (Fig. 7b). One can notice thatneither the contact with the PS layer nor the honeycombmorphology were found to noticeably affect the lumines-cence feature of the QDs nanocrystals (maximum of nano-crytals CdTe photoemission at 656 nm in bulk or adsorbedonto PS honeycomb). Tsai et al. [99] demonstrated the fab-rication of honeycomb structures based on a functionalizedPPV, poly(2,5-bis(3-(N,N-diethylamino)-1-oxapropyl)-1,4-phenylenevinylene) (P1) chlorobenzene solution, usingthe breath figure technique. This conjugated polymer(Mw = 10,500 g mol�1), when dissolved in chlorobenzene,featured absorption and photoluminescence (PL) spectrapeaking at 503 nm and 565 nm, respectively. The P1-basedhoneycomb demonstrated charge transfer when the hon-eycomb was complexed with organic NPs, as fullerenes(C60), either by electrostatic interaction (P1/C60 honey-comb hetero-junction) or in blend. It was demonstratedthat the P1-honeycomb-patterns exhibit highly intenseand red-shifted (peak at 600 nm) photoluminescence com-pared to that of the drop-casted P1 films, likely reflectingregions of ordered close packing or enhanced p–p stackingbetween polymer chains [99]. Thus, an enhancement of thecharge transfer was found through photoluminescencequenching upon complexation of P1-honeycomb with ful-lerene, either in hetero-junction or in blend. Such behavior,combined with the high transparency of this frameworkdue to the large size of the pores (3–4 lm), could beexploited in the future for the fabrication of photovoltaicwindows, sensors, or organic solar cells [99]. Yabu et al.[113] described the fabrication and electroless plating ofregular porous and pincushion-like polymer structuresprepared by self-organization under humid air. After depo-sition of the Pt/Pd catalyst layer, the film was soaked intoan aqueous solution of silver nitrate. After thermal decom-position or solvent elution of the template polymer, uniquemetal mesoscopic structures were obtained.

Fig. 8. (Top) Fabrication diagram of well-ordered porous nanocomposite polymer films and (bottom) SEM images of P(St-BA-AA)/silica nanocompositefilms with various thickness (a) 72 lm, (b) 23 lm, and (c) 4 lm. Drying conditions: 120 �C for 2 h [117].

1014 P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025

A slightly different process was used by Karthaus et al.who chose a poly(styrene-co-maleic anhydride) copolymerto create a patterned zinc oxide ZnO films by BF templating[106]. This copolymer can be chemically cross-linked by a1,8-diamino octane to produce a thermally stable honey-comb film, as already mentioned [46]. As the metal oxideprecursor, zinc acetylacetonate hexahydrate Zn(acac)2

was used and upon heating in vacuum, the complex evap-orated and then adsorbed onto the micro-patterned sub-strate. After pyrolysis of the PS-co-PMA organic matter,this process created an inorganic honeycomb-patternedfilm presenting an enhanced photo-catalytic activity. In-deed, an increase in surface area first facilitated the diffu-sion of photo-generated reactive species from the surfaceand the diffusion of reactants into the porous photo-cata-lytic structure. The second advantage of that microporousstructure was the strong light scattering of the HC struc-ture. This led to multiple passes of photons through thefilm, thus increasing the photo-catalytic efficiency [106].

Here, we can also mention the possibility to use thehoneycomb films to elaborate hybrid pincushion filmsarranging pillar structures hexagonally. Such structureswere prepared by peeling off the top layer of the honey-comb-patterned films. The preparation of zinc oxide[114] or silver [115] ‘‘spikes’’ structure films by using elec-troless deposition method or vacuum deposition, respec-tively, onto the polymer pincushion were described bybottom-up techniques.

4.4. Highly structured hybrid honeycomb films by a non usualprocess

A novel and facile method for the fabrication of nano-composite films with ordered porous surface structures

was developed by Wu and co-workers [116–117]. In thisapproach, a water-borne poly(styrene-co-butylacrylate-co-acrylic acid) P(St-BA-AA)/silica nanocomposite disper-sion was first synthesized by emulsion polymerization.The emulsion was subsequently cast on a substrate andforced-dried at high temperature was applied. A hexago-nal ordered porous structure can be directly obtained onthe surface of the nanocomposite film (Fig. 8).

The pore size and the pore-to-pore distance can bemodulated by the particle size of polymer latex. Indeed,when the particle diameters of the polymer latex were160, 270 and 390 nm, the mean pore diameters 105,210 and 280 nm with an average distance of 160, 280and 370 nm, respectively. We can notice that pore diam-eters are smaller than the ones commonly observed inHC film casted from volatile organic solvent in thepresence of humid airflow (BF method [2–3]). Comparedto conventional BF method, this approach apparentlypresents some unique characteristics and advantages:(i) the ordered porous polymeric films can be obtaineddirectly from water-borne polymer system; therefore, itis very simple and environmentally friendly, (ii) thisapproach can be used for the mass production of porouspolymeric films and (iii) the pore-size distribution is verynarrow, and the size of the pores can be easily tailoredby adjusting the drying temperature and the respectivediameters of the polymer latex. This is the only exampleof the fabrication of an ordered porous nanocompositeand polymeric film from a water-borne system withoutthe use of either a template or a solvent [116–117].Nevertheless, only one latex with a specific compositionof film forming polymer (low Tg), high Tg (PS) andhydrophilic monomer (acrylic acid) has been usedyet.

Fig. 9. Confocal microscopy images of films cast from a mixture of amphiphilic b-galactose-based copolymer and 6-arm star polystyrene: (A) top section offilm and (inset) cross section of film conjugated with fluorescent PNA; (B) top section of film and (inset) cross section of film loaded with fluorescent ConA;(C) top section of film cast from non-functionalized 6-arm star polystyrene only loaded with fluorescent PNA [126].

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1015

5. Fluorescence in honeycomb polymer films

The fabrication of honeycomb patterned microporousfilms with luminescent properties prepared by the breathfigure technique has gain interest since the last years[53,118–124]. Fluorescent polymers bearing lateral pen-dant groups [53,119,123], diblock [118,125], star-shaped[124], hyperbranched [55] fluorescent copolymers weredesigned to form photoluminescent honeycomb polymerfilms. Other studies took advantage of the selective bindingbetween fluorescent molecules and moieties of the poly-mer chains forming the film in order to highlight the loca-tion of the polar groups inside the organized porous film[120,122–123,126]. For instance, proteins have the abilityto conjugate selectively to the polar carbohydrate moietiesof amphiphilic glycopolymers. The confocal fluorescencemicroscopy characterization of the micropatterned poroussurface cast from polymer mixture demonstrated theselective enrichment of the anchored fluorescing proteinin the inner part of the pores (Fig. 9) [126]. The biofunc-tional polymer film showed a selective immobilization ofthe peanut agglutinin (PNA) lectin on the b-galactose moi-eties whereas no interaction with the Concanavalin A (ConA) was observed. (Fig. 9) [126]. The accessibility of the hy-droxyl groups of carbohydrate residues in the surface ofthe pores was also highlighted by the reaction of Rhoda-mine isocyanate with carbohydrate residues [122].

One of the key issues in the elaboration of functionalpolymer film is the orientation of polymer chains towardsthe surface to reveal some functional active chemicalgroups. The mechanism of honeycomb film formation bybreath figure occurring in a wet environment is then anefficient simple approach to achieve the preparation offunctionalized patterned polymer film with a spontaneousregular distribution of the polar groups localized in thevicinity of the cavities [120,123]. With this idea, Galeottiet al. designed functionalized honeycomb films either fromamino-terminated polystyrene where amino functionsreacted with fluorescent dyes or directly from fluorescentlabeled amino-polystyrene [120]. The fluorescence micros-copy image evidenced that fluorescence response is higherinside the cavities, indicating the higher concentration ofthe polar amino groups in the pores [120]. After a thermaltreatment of the fluorescent tagged PS honeycomb film,flat films with spots of fluorescent dye arranged in thesame position as the native cavities were recovered[120]. One can mention that ToF-SIMS (time of flight sec-ondary ion mass spectrometry) imaging was also a power-ful method to highlight the presence of polar p-toluenesulfonate piperidinium end group in the vicinityof the pores of polystyrene honeycomb films [127].

Highly ordered luminescent films prepared by the BFapproach from self-assembly of conjugated copolymershave also attracted scientific interest for the last four years

Fig. 10. (a) FE-SEM image of cross-section structure of PF7-b-PSA166 orderbubble array film tilted at 45� (b) 3D reconstruction image via scanninglaser confocal microscopy of PF7-b-PSA166 microporous film [125].

1016 P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025

[53,55,118–119,124–125]. Polyfluorene based diblockcopolymers [118,125], star shape polymers with styrene-fluorene moiety [124], alternated polyfluorene copolymerbearing tetrahydropyranyl groups on its lateral chains[53] and spiropyran functional polymers [119] proved tobe suitable polymers for the elaboration of micropatternedporous polymer films. Scanning electron microscopy(SEM) has been the most widely used technique to confirmthe organization of these honeycomb films [53,119,124].Field electron SEM images can evidence more preciselythe cross section morphology of HC film based for instanceon poly(2,7-(9,9-dihexylfluorene))-b-poly(stearyl acrylate)(PF-b-PSA) diblock copolymers (Fig. 10) [125]. Laser confo-cal fluorescence microscopy was the method of choice toshow the uniform emission of fluorescent polymers inthe ordered porous film as depicted in Fig. 10 for the PF-b-PSA diblock copolymer [53,118,124–126].

The photoluminescent properties of the selectedpolymer films were shown by UV-visible absorption andemission spectra [55,119,124–125]. A first example ofphoto-responsive honeycomb films was published by_Connal et al. using a photochromic polymer synthesizedby the derivatization of poly(acrylic acid) with 2-(30,30-di-

methyl-6-nitro-30H-spiro-[chromene-2,20indol]-10-yl)-ethanol [119]. Hsu et al. compared the photophysical prop-erties of ordered microporous polymer films and spincoated films prepared from star-shaped styrene fluorenepolymers [124]. The absorption and emission peak maximaexhibited a bathochromic shift of ca. 20 nm between thespin coated film and the porous structured film, indicatingan enhancement of the p-interaction between polymerchains in the HC film [124].

6. Biomaterials based on honeycomb polymer films

In recent years, synthetic glycopolymers (i.e. polymerscarrying pendant carbohydrate moieties) and natural poly-saccharides such as cellulose have received increasingattention especially for bio-surface or bio-active engineer-ing. Since the last five years, many efforts have been donein this direction using the breath figure method to formbiofunctional porous polymer films. It has been shown thathoneycomb polymer films have favorable effect on cell-biomaterial interaction supporting the improvement of cellattachment by structured surfaces [18,77,128–132].Through immobilization of bio-active counterpart, thestructured surface can play a role in biomolecule sensing.The following section will be divided in two parts. The firstone will deal with honeycomb films decorated with carbo-hydrate moieties coming from either natural polysaccha-ride or synthetic glycomonomers. The second part willdeal with biosensing (complexation with protein or glu-cose) in honeycomb porous polymer films.

6.1. Honeycomb films decorated with glycopolymers

The first report on honeycomb porous film containingcarbohydrate moieties was carried out in 2005 by Hernan-dez-Guerrero et al. [15]. In this work cellulose grafted poly-styrene was synthesized using Reversible AdditionFragmentation Transfer (RAFT) polymerization of styreneinitiated from a cellulose backbone derivatized with a dith-iobenzoate RAFT agent. Results showed that the more reg-ular honeycomb films were obtained for high PS content.The resulting films were flexible and also insoluble in manyusual solvent. Liu et al. [133] synthesized ethyl cellulose(EC) graft copolymers by Atom Transfer Radical Polymeri-zation (ATRP) with either polystyrene (PS) or poly(tert-bu-tyl acrylate) (PtBA) or poly(ethylene glycol methacrylate)(PEGMA) side chains. The authors studied the influence ofsolution concentration, relative humidity, percentage ofstyrene on pores sizes and pore size distribution in the hon-eycomb films [133]. No ordered porous films were obtainedin the case of EC-g-PtBA and EC-g-P(PEGMA) due to, respec-tively, the low glass transition temperature of PtBA and thehydrophilicity of the P(PEGMA) side chains. For EC-g-PScopolymers, ordered porous films were obtained with a rel-ative humidity above 60% and polymer solution concentra-tion ranging between 5 and 15 g/L. Honeycomb porousfilms can also be decorated with carbohydrate moietiesfrom synthetic glycopolymers. Indeed, HC films with carbo-hydrate functionalized pores were obtained from diblock,statistical, gradient or comb-like copolymers based on

Table 2Chemical structures of various glycomonomers and the corresponding polymers used for the design of honeycomb porous films.

Ref. Monomer chemical structure Name Polymerizationmethod

Final copolymer

[126]

O

OAc

oAc

AcO

AcOO

OO

2-(20 ,30 ,40 ,60-tetra-O-acetyl-b-D-galactosyloxy)ethyl methacrylate(AcGalEMA)

NMP PS-b-P(AcGalEMA-co-S)

[134]

O

OAc

OAcAcOO

OO

OAc

2-(2-,3-,4-,6-tetra-O-acetyl-b-D-glucosyloxy) ethyl methacrylate (AcGEMA)

ATRP PS-b-PAcGEMA PS-co-PAcGEMAPS-b-(PHEMA-g-PAcGEMA)

[122]O

O

NH

O

OH

OHHOHO

O

O

2-(((D-glucosamin-2-N-yl)carbonyl)oxy)ethyl acrylate (HEAGl)

SFRP P(S-co-HEAGl)

[27]

O

OAc

OAcAcOO

OO

OAc

2-(20 ,30 ,40 ,60-tetra-O-acetyl-b-D-galactosyloxy)ethyl acrylate (AcGalEA)

RAFT PS-b-PAcGalEA PS-b-P(S-grad-AcGalEA) PS-co-PAcGalEA

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1017

glucose or galactose (meth)acrylates [27,122,126,134]. Thecopolymers of styrene and carbohydrate monomer weresynthesized by different controlled radical polymerizationtechniques such as Nitroxide Mediated Polymerization(NMP), ATRP, RAFT or stable free radical polymerization(SFRP) (see Table 2).

Ting et al. implemented NMP to synthesize poly(styrene-b-(2-(20,30,40,60-tetra-O-acetyl-b-D-galactosyloxy)-ethyl methacrylate)-co-styrene) (PS-b-P(AcGalEMA-co-S)block copolymers with a content of galactose-based mono-mer higher than 50 mol-% [126]. After the deacetylationstep of the AcGalEMA moieties, irregular porous films werefabricated from this amphiphilic copolymer. The poorquality of ordering was ascribed to the decrease of the sur-face tension caused by the amphiphilic block copolymer,leading to the coalescence of the water droplet. By mixinga 6-arm star PS with the amphiphilic block glyco-copoly-mer (1:1 w/w), the regularity of the hexagonal array wasenhanced. Ke et al. [134] synthesized by ATRP poly(styrene)-poly(2-(2-,3-,4-,6-tetra-O-acetyl-b-D-glucosyloxy)ethyl methacrylate) (PS-AcGEMA) linear block or random

copolymers and PS-b-(PHEMA-g-AcGEMA) comb-likecopolymers. The influence of the polymer architecture onthe porous HC films was investigated to conclude thatblock and comb like copolymers had great ability to formHC porous film while the random copolymer HC filmexhibited highly disordered pores [134]. A similar studywas conducted by Muñoz-Bonilla et al. [122] with statisti-cal poly(styrene-co-2-(D-glucopyranosyl)aminocarbonyl-oxy ethyl acrylate) (P(S-co-HEAGl)) synthetized byconventional free radical copolymerization. Mixtures of10–50 wt% of amphiphilic copolymer and 90–50% of poly-styrene (Mn = 250,000 g mol�1) were dissolved in THF toform honeycomb porous films by spin-coating castingtechnique under controlled relative humidity (40% or57%) [122]. By controlling parameters such as humidity,temperature and composition of the blend, the authorsprepared surfaces with different pore size and distribution.Escalé et al. recently designed gradient, statistical andblock amphiphilic glyco-copolymers to explore the impactof the polymer chain microstructure on the HC porous filmmorphology [27]. The copolymers were synthesized by

0.161 µm

-0.626 µm

0.286 µm

-0.604 µm

0.052 µm

-0.225 µm

0.081 µm

-0.211 µm

0.116 µm

-0.391 µm

0.097 µm

-0.397 µm

A B C

Fig. 11. Upper line: AFM topography images (10 � 10 lm) of honeycomb porous films from PS-b-PGalEA, PS-b-P(S-grad-GalEA) and P(S-stat-GalEA) in CS2

at 5 g L�1 (from A to C). Bottom line: AFM topography images of honeycomb films obtained with mixture of PS-b-PGalEA, PS-b-P(S-grad-GalEA) or P(S-stat-GalEA) with linear PS (1:1 w/w) (from A to C) from reference [27].

1018 P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025

RAFT polymerization using styrene and 2-(20,30,40,60-tetra-O-acetyl-b-D-galactosyloxy)ethyl acrylate (AcGalEA). Theauthors showed the great potential of gradient copolymeralone to form ordered porous polymer film [27]. On theother hand, statistical copolymers displayed a disorderedporous structures with an additional small porosity ob-served for the amphiphilic diblock copolymer (Fig. 11),which was ascribed to the presence of inverse micelles.

6.2. Biosensing from HC polymer films

Specific properties of HC films as biomaterials are pro-vided by the BF method in humid atmosphere which in-duces a specific location of the polar groups at thesurface of the pores (as shown in Section 5). Then, HC filmshave shown the ability to play a role in sensing biomole-cules such as proteins through the presence of the sugarfunctions at the pore surface. The bioactivity of the amphi-philic glycopolymer based HC films was explored throughthe conjugation of the carbohydrate moieties with specificproteins. For instance, Ting et al. [126] highlighted by con-focal fluorescence microscopy the selective conjugation ofpeanut agglutinin (PNA) with the b-galactose moieties ofthe functionalized porous films. On the other hand, studieson lectin recognition on honeycomb-patterned films dem-onstrated that glucose-containing films can specificallyrecognize Concanavalin A (ConA) [122,134].

Another strategy to afford bio-activity to the HC filmconsists in taking advantage of the polar group orientationto post-functionalize the HC pore surface. In the work ofMin et al. [135], honeycomb films were first elaboratedwith poly(styrene-b-acrylic acid) (PS-b-PAA) block copoly-mer and subsequently functionalized with a biotin-strep-tavidin complex. Biotinylated Escherichia coli bacteriacells were selectively immobilized inside the pores. Li etal., using commercially available poly(styrene-b-butadi-

ene-b-styrene) triblock copolymer, elaborated solventand thermal resistant honeycomb film through photo-chemical cross-linking. This step led to the formation ofpolar groups on the surface of the HC films, which werefound to be suitable for cell attachment for pore size of3 lm [136]. Nystrom et al. synthesized star and linear PSby ATRP to form honeycomb films [137]. The living poly-mer chain ends at the surface were then used to insertpoly(glycidyl methacrylate) (PGMA) chains by a grafting-from approach. As mentioned in this study, the morphol-ogy of the porous film can be affected by the graftingexperimental conditions (nature of the solvent and mono-mer concentration), the main issue being the film dissolu-tion during the polymerization process [137]. Resultsshowed that the monomer concentration had to remainlow (from 50 to 25 vol.%) and water was the most appro-priate solvent. In order to confirm the presence of sur-face-grafted GMA, attenuated total reflectance-infrared(ATR-IR) was used on the dry films. Moreover, SEM imag-ing showed the distortion induced by the grafting yieldssince high grafting yields led to distorted films. The bio-functionalization of the pores was then performed by anepoxy-amine click reaction between amine-biotin andPGMA moieties. Sensing property of the HC film was dem-onstrated by further binding with Cy5-labeled streptavidin[137]. Ke et al. [138] functionalized the hydroxyl groups ofpoly(styrene-b-hydroxyethyl methacrylate) (PS-b-PHEMA)honeycomb film with 2-bromoisobutyryl bromide. Surfaceinitiated ATRP of 2-(2-,3-,4-,6-tetra-O-acetyl glucosyl-oxy)ethyl methacrylate) (AcGEMA) was carried out fromthe halogenated surface groups. ATR-IR, X-ray photoelec-tron spectroscopy (XPS) and AFM were used to confirmthe grafting efficiency [138]. Min et al. performed sur-face-initiated RAFT copolymerization of N-isopropyl acryl-amide (NiPAAm) and N-acryloyl glucosamine from cross-linked poly(styrene-co-maleic anhydride) honeycomb film

80

100

120

140

pH 9

50

60

70

80

90

100

110

0 1 2 3 4

CA

s (º

)A

s (º

)

Cycle

pH 3

pH 9

A

B

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1019

[46]. In both studies [46,138], Concanavalin A was used toshow the film bioactivity via its specific recognition withsugar groups. It is interesting to note that the conjugationwith the lectin can be controlled by temperature from thethermo-responsive character of the PNIPAAm-co-PAGArandom copolymer grafted chains. Above the lower criticalsolution temperature (LCST), the copolymer collapsedexposing the sugar hydrophilic moieties to the environ-ment while below the LCST the hydrated chains interferedwith the conjugation between glucose and ConA. Conse-quently, below the LCST, the conjugation was switchedoff, whereas above it, the glucose moieties/lectin bindingbecame stronger [46].

Chen et al. described the design of phenylboronic acid(PBA) based segregated patterned porous film for glucosesensing [139]. First, the hydrophobic polystyrene-b-poly(-methyl acrylate) (PS-b-PMA) diblock copolymer was syn-thesized by ATRP. After the hydrolysis of the methylacrylate moieties into acrylic acid (AA), the PBA pendantgroups were incorporated into the polymer chain by thereaction between 3-aminophenylboronic acid and poly(-acrylic acid), leading to polystyrene-b-poly(acrylic acid-co-acrylamidophenylboronic acid) (PS-b-P(AA-co-AAPBA))with different contents of PBA pendant groups. The PS-b-P(AA-co-AAPBA) was dissolved in carbon disulfide to formthe HC film by BF method [139]. The PBA-functionalizedHC films showed glucose sensing ability. Fluorescencespectroscopy was used to confirm the bioactivity of thefilm with Alizarin Red S (ARS) as probe. First the probewas immobilized onto the honeycomb film taking into ac-count that the formation of ARS–PBA complex increasedgreatly the fluorescence intensity of ARS. Considering thatthe association constant between ARS and PBA is 282 timeshigher than the one between glucose and PBA at pH 7.4, anexcess of glucose was then used to replace the immobilizedARS. As a consequence of the replacement, the fluorescencewas quenched, meaning the effectiveness of the glucosesensing. A quartz crystal microbalance (QCM) was alsoused to investigate the amount of attached glucose in thefilm [139]. Results showed that the binding of PBA withglucose was more effective when the surface was pre-wet-ted with ethanol in order to reveal the OH group. Indeed,the oscillation frequency shift increased largely in compar-ison with the non-wetted HC films [139]. Recently, Zhanget al. proposed an original method to produce in one-stepprotein-containing ordered HC films by introducing pro-teins into an inverse emulsion stabilized with an PS-b-PHEMA block copolymer [140]. By this way, multisteppreparation including synthesis, patterned film fabricationand bio-molecule immobilization was performed in onestep which could be time saving.

0

20

40

60

0 1 2 3 4Cycle

pH 3C

Fig. 12. Reversibility of contact angles (CAs) of a water droplet depositedonto (A) PS-b-P4VP honeycomb film and (B) PS-b-P4VP micro-pillardedfilm from reference [78].

7. Functional materials based on honeycomb porousfilms

7.1. Smart honeycomb porous surface responsive to anexternal stimuli

BF method allowed for the preparation of ordered mi-cro-patterned surfaces sensitive to an external stimulus

such as solvent, pH or temperature to provide new smartsurfaces.

Cui et al. proposed several studies on the design ofreversible honeycomb membranes based on polystyrene/poly(2-vinylpyridine) (PS/P2VP) mixture phase separation[141–145]. Two kinds of structures were obtained depend-ing on the post-solvent treatment of the honeycomb filmby immersion into water or by solvent vapor annealingwith carbone disulfide (CS2), toluene, tetrahydrofurane(THF), dimethylformamide (DMF) or methylethyl ketone(MEK). When the atmosphere was P2VP selective (water,DMF, MEK), island-like patterned surface was observed,whereas classical honeycomb porous surface was obtainedwhen the atmosphere was PS selective (THF, CS2, Toluene).A reversible behavior was observed by changing the natureof the solvent.

The elaboration of thermo-sensitive honeycomb porousfilms has emerged since 2008 with the work of Stenzel andco-workers [128]. For that purpose, thermo-responsivePNiPAAm polymer chains were grafted via surface-initi-ated RAFT polymerization from honeycomb porous filmsprepared with a comb-like polystyrene and a randomcopolymer composed of styrene and 2-hydroxyethyl meth-acrylate. The polymerization was carried out under c-irra-diation in water in the presence of a trithiocarbonate RAFTagent [128]. Contact Angle (CA) measurements were usedto confirm the presence of thermo-responsive polymerchains on the surface of the HC films and to show the

Fig. 13. Schematic illustration and scanning electron micrograph of (a) the honeycomb-patterned film, (b) the peeling process, and (c) the pincushionstructure, from reference [17].

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switchable hydrophilic/hydrophobic behavior. The aim forthese specific grafted films was to study the controlledadhesion of proteins or bacteria onto the biomaterialsfilms. As mentioned above in the part dealing with sensingproperties, a similar approach of grafting thermo-respon-sive polymer chains from HC films was investigated bythe same research group to design ‘‘thermo-dependentswitcher’’ for lectin conjugation [46]. In 2009, Yabu et al.[146] proposed the fabrication of thermo-responsive hon-eycomb and pincushion films based on a mixture of PSand poly(N-dodecylacrylamide-co-N-isopropyl acrylam-ide). The investigation of water CA as a function of temper-ature highlighted the thermo-sensitive character of thepolymeric surface. In the case of honeycomb structuredfilms, no discernable change in the contact angle was ob-served whereas in the case of the pincushion structuredfilms, a thermo-responsive behavior was observed with achange in CA from 90� at 10 �C (T < LCST, hydrophilic poly-mer) to 150� at 35 �C (T > LCST, hydrophobic polymer).

Wang et al. [63] proposed the design of HC porous filmwith a wettability behavior depending on pH. In this work,

polystyrene-b-poly(acrylic acid) (PS-b-PAA) was used forthe porous film formation. First, the authors investigatedthe effect of the pore size on the wettability behavior.When the pore size was 1.5 lm the transition betweenhydrophobic and hydrophilic state was faster than thetransition observed in the case of lower pore size of0.4 lm. This behavior was attributed to the fact that thewater can penetrate easily by capillary action when thepores are larger [63]. Second, the authors investigatedthe effect of the water solution pH on the kinetic of thewettability transformation (between 0 and 180 s). Thetransition between hydrophobic and hydrophilic statewas observed to be faster for buffer solution at pH 10(10 s) in comparison with buffer solution at pH 4 (130 s)[63]. This behavior was explained by the acceleration ofPAA ionization at high pH.

Another approach to design pH sensitive honeycombporous surface was investigated by Escalé et al. [78] usinga well-defined polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer synthesized by nitroxyde-medi-ated polymerization. The diblock copolymer was designed

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1021

to favor nanophase separation of both immiscible blocksduring the film formation under humid atmosphere (BFmethod) by polymer self-assembly. AFM images confirmedthe formation of highly structured HC films obtained fromchloroform solutions cast onto either glass or water under40–50% of RH. The segregation between the two blocks ledto P4VP cylinders in a matrix of PS in between the pores(Fig. 3). As the P4VP phase is sensitive to pH (pKa = 5.2), avariation of the contact angle with pH of the water dropletwas observed and the gap between pH 3 and pH 9 was en-hanced for micro-pillarded surface obtained by peeling-offthe HC film (Fig. 12). Through this strategy, Billon and co-workers showed for the first time HC films exhibited areversible pH-responsive behavior [78].

As a conclusion of this part, either mixtures of polymers[141–146] or diblock copolymers [63,78] or grafted poly-mer chains [46,128] were used to form stimuli-responsivestructured polymer films. The reversibility of thestimuli-responsive behavior was observed only in fewexamples like in the work of Cui et al. [141–145] for sol-vent dependent films or in the study of Escalé et al. [78]for pH-sensitive structured films. Moreover, in the lastexample, hydrophobic or hydrophilic state was stable forseveral minutes while the HC surface became systemati-cally hydrophilic after seconds in the work of Wang et al.[63] without proof of reversibility.

7.2. Superhydrophobic honeycomb porous films

In 2005, Yabu et al. proposed an original method to pro-duce superhydrophobic honeycomb patterned films [147].Indeed, fluorinated based polymers were used to designthe porous structure by BF method. Moreover, by using aspecial coating technique, the film thickness was con-trolled and transparent films were made by controllingthe size of the pore. Indeed, a metal blade was fixed per-pendicularly to the fluorinated substrate and the solutionwas casted onto one side of the blade. Then the substratewas moved horizontally from the other side giving a thinliquid film from the narrow gap between the metal bladeand the substrate. Humid air (relative humidity of 60% atroom temperature) was applied to the solution surfacewith a flow velocity of 10 L/min. The film thickness was ad-justed to less than 100 lm by changing the distance be-tween the blade edge and the substrate. In order toincrease the hydrophobicity behavior, Yabu et al. designedpincushion structures by peeling off the tops of the honey-comb films using tape (Fig. 13) [17]. By this way, superhy-drophobic behavior was achieved with water contact angleclose to 170�.

Another technique developed by Zander et al. [148] wasused to produce superhydrophobic surface. In this case,micro-pillarded silicone surfaces were obtained by usingthe regular arrays of HC film pores as templates. The sili-cone pillared surfaces showed a high water CA of 142�.

8. Conclusions

Structuring polymer surface by the simple bottom upbreath figure (BF) method has proved to be a relevant

process to design honeycomb (HC) porous polymer filmsexhibiting a hexagonal array of pores in the range of 0.5–4 lm. A large range of polymers has been used to targetdifferent surface properties such as for instance irides-cence, photoluminescence, cell adhesion, bio-moleculerecognition, intrinsic properties of hybrid films, stimuli-responsive structured surfaces, superhydrophobic charac-ter of surfaces derived from HC films. It can be noted thatBF has proved to be a powerful method to induce a sponta-neous orientation of either polar groups or hybrid particlesdue to the solvent/water interface intrinsically formed dur-ing the fast solvent evaporation under humid atmosphere.It has been shown that functionalization of pore surfacecan also be performed by surface-initiated polymerizationof different monomers from the HC film in order to intro-duce grafted polymer chains. Despite the simple fast pro-cedure of honeycomb film formation, it should be notedthat several parameters can play a role in the HC filmmorphology influencing for instance pore size or qualityof ordering. Consequently, it is important to set up for eachpolymer/solvent system the influence of relative humidity,polymer concentration, drying rate, nature of substrate. Fora given nature of polymer, the macromolecular architec-ture and microstructure are also key parameters. Never-theless, from all the published studies, the followingtrends have been drawn: hydrophobic solvents exhibitinghigh vapor pressure are the best candidates and hydropho-bic polymers showing a complex structure or able to self-assemble seem to be the most robust systems to promotethe fast precipitation of the thin polymer layer at thewater/solution interface. The interfacial tension and thenature of the substrate also impact the HC film formationbut the exact influence of these both parameters has stillto be better understood. The efforts devoted to the polymercross-linking inside the HC film opens the way of potentialapplications which require stability of the film against sol-vent and temperature. In most of the studies recentlydeveloped by different research groups, the authors pro-duced a variety of micro-patterned porous polymer filmthrough BF method in order to design functional surfaces.They took advantage of either the pore ordering and/orthe chemical moieties orientation at the pore surfaceand/or the intrinsic properties of the chosen polymers orhybrid nanoparticles to propose a wide pallet of fascinatingpolymeric surfaces. The combination of two self-organiza-tion processes at various length scales opened a new routeto prepare hierarchically structured HC film from eitherblock copolymer self-assembly or nanoparticles assembly.By the simple BF approach, entire inorganic or hybrid in-verse opals have been synthesized thanks to the widerange of available polymeric systems. BF method allowsthe preparation of patterned porous polymer films exhibit-ing surface in the range of cm2. Nevertheless, from theintrinsic dynamic mechanism BF by solvent evaporation,the morphology of HC film is known to vary from the edgeto the center of the film. This aspect has to be controlledand optimized to envisage the study of such well-orga-nized surfaces as model substrates in order to understandthe impact of film morphology on adhesion, sensing, pho-tonic or optical phenomena for instance.

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References

[1] Widawski G, Rawiso M, Francois B. Self-organized honeycombmorphology of star-polymer polystyrene films. Nature1994;369(6479):387–9.

[2] Bunz UHF. Breath figures as a dynamic templating method forpolymers and nanomaterials. Adv Mater 2006;18(8):973–89.

[3] Stenzel MH, Barner-Kowollik C, Davis TP. Formation of honeycomb-structured, porous films via breath figures with different polymerarchitectures. J Polym Sci A – Polym Chem 2006;44(8):2363–75.

[4] Briscoe BJ, Galvin KP. An experimental study of the growth of breathfigures. Colloids Surf 1991;56:263–78.

[5] Steyer A, Guenoun P, Beysens D, Knobler CM. Two dimensionalordering during droplet growth on a liquid surface. Phys Rev B1990;42(1):1086–9.

[6] Limaye AV, Narhe RD, Dhote AM, Ogale SB. Evidence for convectiveeffects in breath figure formation on volatile fluid surfaces. PhysRev Lett 1996;76(20):3762–5.

[7] Francois B, Pitois O, Francois J. Polymer films with a self-organizedhoneycomb morphology. Adv Mater 1995;7(12):1041–4.

[8] Srinivasarao M, Collings D, Philips A, Patel S. Three-dimensionallyordered array of air bubbles in a polymer film. Science2001;292(5514):79–83.

[9] Xu S, Li M, Mitov Z, Kumacheva E. Surface textures induced byconvection in thin films of polymeric and polymerizable fluids. ProgOrg Coat 2003;48(2–4):227–35.

[10] Stenzel-Rosenbaum MH, Davis TP, Fane AG, Chen V. Porouspolymer films and honeycomb structures made by the self-organization of well-defined macromolecular structures createdby living radical polymerization techniques. Angew Chem Int Ed2001;40(18):3428–32.

[11] Hayakawa T, Horiuchi S. From angstroms to micrometers: self-organized hierarchical structure within a polymer film. AngewChem Int Ed 2003;42(20):2285–9.

[12] Song L, Bly RK, Wilson JN, Bakbak S, Park JO, Srinivasarao M, et al.Facile microstructuring of organic semiconducting polymers by thebreath figure method: hexagonally ordered bubble arrays in rigid-rod polymers. Adv Mater 2004;16(2):115–8.

[13] Bolognesi A, Mercogliano C, Yunus S, Civardi M, Comoretto D,Turturro A. Self-organization of polystyrenes into orderedmicrostructured films and their replication by soft lithography.Langmuir 2005;21(8):3480–5.

[14] Cheng CX, Tian Y, Shi YQ, Tang RP, Xi F. Ordered honeycomb-structured films from dendronized PMA-b-PEO rod–coil blockcopolymers. Macromol Rapid Commun 2005;26(15):1266–72.

[15] Hernandez-Guerrero M, Davis TP, Barner-Kowollik C, Stenzel MH.Polystyrene comb polymers built on cellulose or poly(styrene-co-2-hydroxyethylmethacrylate) backbones as substrates for thepreparation of structured honeycomb films. Eur Polym J2005;41(10):2264–77.

[16] Yabu H, Shimomura M. Simple fabrication of micro lens arrays.Langmuir 2005;21(5):1709–11.

[17] Yabu H, Takebayashi M, Tanaka M, Shimomura M.Superhydrophobic and lipophobic properties of self-organizedhoneycomb and pincushion structures. Langmuir 2005;21(8):3235–7.

[18] Beattie D, Wong KH, Williams C, Poole-Warren LA, Davis TP,Barner-Kowollik C, et al. Honeycomb-structured porous films frompolypyrrole-containing block copolymers prepared via RAFTpolymerization as a scaffold for cell growth. Biomacromolecules2006;7(4):1072–82.

[19] Deepak VD, Asha SK. Self-organization-induced three-dimensionalhoneycomb pattern in structure-controlled bulky methacrylatepolymers: synthesis, morphology, and mechanism of poreformation. J Phys Chem B 2006;110(43):21450–9.

[20] Karikari AS, Williams SR, Heisey CL, Rawlett AM, Long TE. Porousthin films based on photo-cross-linked star-shaped poly(D,L-lactide)s. Langmuir 2006;22(23):9687–93.

[21] Qu G, Jiang FF, Zhang SY, Usuda SJ. A novel poly(p-phenylenevinylene)-b-poly(methyl methacrylate) rod–coil diblockcopolymer. Mater Lett 2007;61(16):3421–4.

[22] Billon L, Manguian M, Pellerin V, Joubert M, Eterradossi O, Garay H.Tailoring highly ordered honeycomb films based on ionomermacromolecules by the bottom-up approach. Macromolecules2009;42(1):345–56.

[23] Lu Y, Ren Y, Wang L, Wang XD, Li CX. Template synthesis ofconducting polyaniline composites based on honeycomb orderedpolycarbonate film. Polymer 2009;50(9):2035–9.

[24] Escale P, Save M, Lapp A, Rubatat L, Billon L. Hierarchical structuresbased on self-assembled diblock copolymers within honeycombmicro-structured porous films. Soft Matter 2010;6(14):3202–10.

[25] Li J, Zhao QL, Chen JZ, Li L, Huang J, Ma Z, et al. Highly orderedmicroporous films containing a polyolefin segment fabricated bythe breath-figure method using well-defined polymethylene-b-polystyrene copolymers. Polym Chem 2010;1(2):164–7.

[26] Chang CC, Juang TY, Ting WH, Lin MS, Yeh CM, Dai SA, et al. Using abreath-figure method to self-organize honeycomb-like polymericfilms from dendritic side-chain polymers. Mater Chem Phys2011;128(1–2):157–65.

[27] Escalé P, Ting SRS, Khoukh A, Rubatat L, Save M, Stenzel MH, et al.Synthetic route effect on macromolecular architecture: from blockto gradient copolymers based on acryloyl galactose monomer usingRAFT polymerization. Macromolecules 2011;44(15):5911–9.

[28] Jiang X, Gu J, Shen Y, Wang S, Tian X. Formation of honeycomb-patterned microporous films based on a fluorinated poly(siloxaneimide) segmented copolymer. J Appl Polym Sci 2011;119(6):3329–37.

[29] Samanta S, Chatterjee DP, Layek RK, Nandi AK. Multifunctionalporous poly(vinylidene fluoride)-graft-poly(butyl methacrylate)with good Li+ ion conductivity. Macromol Chem Phys2011;212(2):134–49.

[30] Lide DR. Handbook of chemistry and physics. 80th ed. BocaRaton: CRC Press; 1999.

[31] Hernández-Guerrero M, Stenzel MH. Honeycomb structuredpolymer films via breath figures. Polym Chem 2012;3(3):563–77.

[32] Dong WY, Zhou YF, Yan DY, Mai YY, He L, Jin CY. Honeycomb-structured microporous films made from hyperbranched polymersby the breath figure method. Langmuir 2009;25(1):173–8.

[33] Peng J, Han YC, Yang YM, Li BY. The influencing factors on themacroporous formation in polymer films by water droplettemplating. Polymer 2004;45(2):447–52.

[34] Ghannam L, Manguian M, Francois J, Billon L. A versatile route tofunctional biomimetic coatings: ionomers for honeycomb-likestructures. Soft Matter 2007;3(12):1492–9.

[35] Xiong XP, Lin MF, Zou WW, Liu XY. Kinetic control of preparinghoneycomb patterned porous film by the method of breath figure.React Funct Polym 2011;71(9):964–71.

[36] Connal LA, Qiao GG. Preparation of porous poly(dimethylsiloxane)-based honeycomb materials with hierarchal surface features andtheir use as soft-lithography templates. Adv Mater 2006;18(22):3024–8.

[37] Connal LA, Gurr PA, Qiao GG, Solomon DH. From well defined star-microgels to highly ordered honeycomb films. J Mater Chem2005;15(12):1286–92.

[38] Connal LA, Vestberg R, Gurr PA, Hawker CJ, Qiao GG. Patterning onnonplanar substrates: flexible honeycomb films from a range ofself-assembling star copolymers. Langmuir 2008;24(2):556–62.

[39] Gao HF, Ohno S, Matyjaszewski K. Low polydispersity star polymersvia cross-linking macromonomers by ATRP. J Am Chem Soc2006;128(47):15111–3.

[40] Blencowe A, Tan JF, Goh TK, Qiao GG. Core cross-linked starpolymers via controlled radical polymerisation. Polymer2009;50(1):5–32.

[41] Helms B, Guillaudeu SJ, Xie Y, McMurdo M, Hawker CJ, Frechet JMJ.One-pot reaction cascades using star polymers with core-confinedcatalysts. Angew Chem Int Ed 2005;44(39):6384–7.

[42] Connal LA, Qiao GG. Honeycomb coated particles: porousdoughnuts, golf balls and hollow porous pockets. Soft Matter2007;3(7):837–9.

[43] Yao X, Yao HW, Li YT, Chen G. Preparation of honeycomb scaffoldwith hierarchical porous structures by core-crosslinked core-corona nanoparticles. J Colloid Interface Sci 2009;332(1):165–72.

[44] Erdogan B, Song LL, Wilson JN, Park JO, Srinivasarao M, Bunz UHF.Permanent bubble arrays from a cross-linked poly(para-phenyleneethynylene): picoliter holes without microfabrication. JAm Chem Soc 2004;126(12):3678–9.

[45] Kabuto T, Hashimoto Y, Karthaus O. Thermally stable and solventresistant mesoporous honeycomb films from a crosslinkablepolymer. Adv Funct Mater 2007;17(17):3569–73.

[46] Min EH, Ting SRS, Billon L, Stenzel MH. Thermo-responsiveglycopolymer chains grafted onto honeycomb structured porousfilms via raft polymerization as a thermo-dependent switcher forlectin concanavalin a conjugation. J Polym Sci A – Polym Chem2010;48(15):3440–55.

[47] Wong KH, Stenzel MH, Duvall S, Ladouceur F. Exploitable flexiblehoneycomb structured porous films from sol–gel cross-linkable

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1023

silicone based random branched copolymers. Chem Mater2010;22(5):1878–91.

[48] Li L, Zhong YW, Li J, Chen CK, Zhang AJ, Xu J, et al. Thermally stableand solvent resistant honeycomb structured polystyrene films viaphotochemical cross-linking. J Mater Chem 2009;19(39):7222–7.

[49] Nakamichi Y, Hirai Y, Yabu H, Shimomura M. Fabrication ofpatterned and anisotropic porous films based on photo-cross-linking of poly(1,2-butadiene) honeycomb films. J Mater Chem2011;21(11):3884–9.

[50] Karthaus O, Hashimoto Y, Kon K, Tsuriga Y. Solvent resistanthoneycomb films from photo-crosslinkable polycinnamate.Macromol Rapid Commun 2007;28(8):962–5.

[51] Li L, Zhong YW, Gong JL, Li JA, Chen CK, Zeng BR, et al. Constructingrobust 3-dimensionally conformal micropatterns: vulcanization ofhoneycomb structured polymeric films. Soft Matter 2011;7(2):546–52.

[52] Li L, Zhong YW, Gong JL, Li JA, Huang J, Ma Z. Fabrication of robustmicro-patterned polymeric films via static breath-figure processand vulcanization. J Colloid Interface Sci 2011;354(2):758–64.

[53] Bolognesi A, Galeotti F, Moreau J, Giovanella U, Porzio W, Scavia G,et al. Unsoluble ordered polymeric pattern by breath figureapproach. J Mater Chem 2010;20(8):1483–8.

[54] Tian Y, Liu S, Ding HY, Wang LH, Liu BQ, Shi YQ. Formation ofhoneycomb-patterned polyetherketone cardo (PEK-C) films in ahighly humid atmosphere. Macromol Chem Phys 2006;207(21):1998–2005.

[55] Ejima H, Iwata T, Yoshie N. Morphology-retaining carbonization ofhoneycomb-patterned hyperbranched poly(phenylene vinylene)film. Macromolecules 2008;41(24):9846–8.

[56] Pitois O, Francois B. Formation of ordered micro-porousmembranes. Eur Phys J B 1999;8(2):225–31.

[57] Dong RH, Yan JL, Ma HM, Fang Y, Hao JC. Dimensional architectureof ferrocenyl-based oligomer honeycomb-patterned films: frommonolayer to multilayer. Langmuir 2011;27(14):9052–6.

[58] Fukuhira Y, Yabu H, Ijiro K, Shimomura M. Interfacial tensiongoverns the formation of self-organized honeycomb-patternedpolymer films. Soft Matter 2009;5(10):2037–41.

[59] Servoli E, Ruffo GA, Migliaresi C. Interplay of kinetics and interfacialinteractions in breath figure templating – a phenomenologicalinterpretation. Polymer 2010;51(11):2337–44.

[60] Saunders AE, Dickson JL, Shah PS, Lee MY, Lim KT, Johnston KP, et al.Breath figure templated self-assembly of porous diblock copolymerfilms. Phys Rev E 2006;73(3).

[61] Wu XJ, Jones MD, Davidson MG, Chaudhuri JB, Ellis MJ. Surfactant-free poly(lactide-co-glycolide) honeycomb films for tissueengineering: relating solvent, monomer ratio and humidity toscaffold structure. Biotechnol Lett 2011;33(2):423–30.

[62] Ferrari E, Fabbri P, Pilati F. Solvent and substrate contributions tothe formation of breath figure patterns in polystyrene films.Langmuir 2011;27(5):1874–81.

[63] Wang CY, Mao YD, Wang DY, Qu QS, Yang GJ, Hu XY. Fabrication ofhighly ordered microporous thin films by PS-b-PAA self-assemblyand investigation of their tunable surface properties. J Mater Chem2008;18(6):683–90.

[64] Kuo CT, Lin YS, Liu TK, Liu HC, Hung WC, Jiang IM, et al. Dynamics ofsingle-layer polymer breath figures. Opt Express 2010;18(17):18464–70.

[65] Ma HY, Tian Y, Wang XL. In situ optical microscopy observation ofthe growth and rearrangement behavior of surface holes in thebreath figure process. Polymer 2011;52(2):489–96.

[66] Ma H, Kong L, Guo X, Hao J. Dynamic insights into formation ofhoneycomb structures induced by breath figures. RSC Adv2011;1(7):1187–9.

[67] Karthaus O, Maruyama N, Cieren X, Shimomura M, Hasegawa H,Hashimoto T. Water-assisted formation of micrometer-sizehoneycomb patterns of polymers. Langmuir 2000;16(15):6071–6.

[68] Song LL, Sharma V, Park JO, Srinivasarao M. Characterization ofordered array of micropores in a polymer film. Soft Matter2011;7(5):1890–6.

[69] Sun H, Li HL, Bu WF, Xu M, Wu LX. Self-organized microporousstructures based on surfactant-encapsulated polyoxometalatecomplexes. J Phys Chem B 2006;110(49):24847–54.

[70] Kojima M, Hirai Y, Yabu H, Shimomura M. The effects of interfacialtensions of amphiphilic copolymers on honeycomb-patternedfilms. Polym J 2009;41(8):667–71.

[71] Harkins WD, Feldman A. Films the spreading of liquids and thespreading coefficient. J Am Chem Soc 1922;44:2665–85.

[72] Zhao BH, Zhang J, Wang XD, Li CX. Water-assisted fabrication ofhoneycomb structure porous film from poly(L-lactide). J MaterChem 2006;16(5):509–13.

[73] Fukuhira Y, Kitazono E, Hayashi T, Kaneko H, Tanaka M, ShimomuraM, et al. Biodegradable honeycomb-patterned film composed ofpoly(lactic acid) and dioleoylphosphatidylethanolamine.Biomaterials 2006;27(9):1797–802.

[74] Tian Y, Jiao QZ, Ding HY, Shi YQ, Liu BQ. The formation ofhoneycomb structure in polyphenylene oxide films. Polymer2006;47(11):3866–73.

[75] Jiang XL, Zhang TZ, Xu LN, Wang CL, Zhou XF, Gu N. Surfactant-induced formation of honeycomb pattern on micropipette withcurvature gradient. Langmuir 2011;27(9):5410–9.

[76] Cheng CX, Tian Y, Shi YQ, Tang RP, Xi F. Porous polymer films andhoneycomb structures based on amphiphilic dendronized blockcopolymers. Langmuir 2005;21(14):6576–81.

[77] Li XF, Wang Y, Zhang LA, Tan SX, Yu XL, Zhao N, et al. Fabrication ofhoneycomb-patterned polyalkylcyanoacrylate films from monomersolution by breath figures method. J Colloid Interface Sci2010;350(1):253–9.

[78] Escalé P, Rubatat L, Derail C, Save M, Billon L. PH sensitivehierarchically self-organized bioinspired films. Macromol RapidCommun 2011;32(14):1072–6.

[79] Munoz-Bonilla A, Ibarboure E, Papon E, Rodriguez-Hernandez J.Engineering polymer surfaces with variable chemistry andtopography. J Polym Sci A – Polym Chem 2009;47(9):2262–71.

[80] Munoz-Bonilla A, Ibarboure E, Papon E, Rodriguez-Hernandez J.Self-organized hierarchical structures in polymer surfaces: self-assembled nanostructures within breath figures. Langmuir2009;25(11):6493–9.

[81] Galeotti F, Chiusa I, Morello L, Giani S, Breviario D, Hatz S, et al.Breath figures-mediated microprinting allows for versatileapplications in molecular biology. Eur Polym J 2009;45(11):3027–34.

[82] Gong JL, Sun LC, Zhong YW, Ma CY, Li L, Xie SY, et al. Fabrication ofmulti-level carbon nanotube arrays with adjustable patterns.Nanoscale 2012;4(1):278–83.

[83] Kim JH, Seo M, Kim SY. Lithographically patterned breath figure ofphotoresponsive small molecules: dual-patterned honeycomb linesfrom a combination of bottom-up and top-down lithography. AdvMater 2009;21(41):4130–3.

[84] Kojima M, Nakanishi T, Hirai Y, Yabu H, Shimomura M. Photo-patterning of honeycomb films prepared from amphiphiliccopolymer containing photochromic spiropyran. Chem Commun2010;46(22):3970–2.

[85] Park JS, Lee SH, Han TH, Kim SO. Hierarchically ordered polymerfilms by templated organization of aqueous droplets. Adv FunctMater 2007;17(14):2315–20.

[86] Nassif N, Livage J. From diatoms to silica-based biohybrids. ChemSoc Rev 2011;40(2):849–59.

[87] Losic D, Mitchell JG, Lal R, Voelcker NH. Rapid fabrication of micro-and nanoscale patterns by replica molding from diatom biosilica.Adv Funct Mater 2007;17(14):2439–46.

[88] Losic D, Mitchell JG, Voelcker NH. Diatomaceous lessons innanotechnology and advanced materials. Adv Mater 2009;21(29):2947–58.

[89] Vamvounis G, Nystrom D, Antoni P, Lindgren M, Holdcroft S, HultA. Self-assembly of poly(9,90-dihexylfluorene) to form highlyordered isoporous films via blending. Langmuir 2006;22(9):3959–61.

[90] Vohra V, Bolognesi A, Calzaferri G, Botta C. Multilevel organizationin hybrid thin films for optoelectronic applications. Langmuir2009;25(20):12019–23.

[91] Boker A, Lin Y, Chiapperini K, Horowitz R, Thompson M, Carreon V,et al. Hierarchical nanoparticle assemblies formed by decoratingbreath figures. Nat. Mater. 2004;3(5):302–6.

[92] Sun H, Li HL, Wu LX. Micro-patterned polystyrene surfaces directedby surfactant-encapsulated polyoxometalate complex via breathfigures. Polymer 2009;50(9):2113–22.

[93] Ma HM, Cui JW, Chen JF, Hao JC. Self-organized polymernanocomposite inverse opal films with combined opticalproperties. Chem – Eur J 2011;17(2):655–60.

[94] Ma HM, Cui JW, Song AX, Hao JC. Fabrication of freestandinghoneycomb films with through-pore structures via air/waterinterfacial self-assembly. Chem Commun 2011;47(4):1154–6.

[95] Nurmawati MH, Ajikumar PK, Renu R, Valiyaveettil S. Hierarchicalself-organization of nanomaterials into two-dimensional arraysusing functional polymer scaffold. Adv Funct Mater 2008;18(20):3213–8.

[96] Wong KH, Davis TP, Barner-Kowollik C, Stenzel MH. Gold-loadedorganic/inorganic nanocomposite honeycomb membranes. Aust JChem 2006;59(8):539–43.

1024 P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025

[97] Nurmawati MH, Renu R, Ajikumar PK, Sindhu S, Cheong FC, Sow CH,et al. Amphiphilic poly(p-phenylene)s for self-organized porousblue-light-emitting thin films. Adv Funct Mater 2006;16(18):2340–5.

[98] Zou JH, Chen H, Chunder A, Yu YX, Huo Q, Zhai L. Preparation of asuperhydrophobic and conductive nanocomposite coating from acarbon-nanotube-conjugated block copolymer dispersion. AdvMater 2008;20(17):3337–41.

[99] Tsai HH, Xu ZH, Pai RK, Wang LY, Dattelbaum AM, Shreve AP, et al.Structural dynamics and charge transfer via complexation withfullerene in large area conjugated polymer honeycomb thin films.Chem Mater 2011;23(3):759–61.

[100] Sun W, Shao Z, Ji JA. Particle-assisted fabrication of honeycomb-structured hybrid films via breath figures method. Polymer2010;51(18):4169–75.

[101] Li J, Peng J, Huang WH, Wu Y, Fu J, Cong Y, et al. Orderedhoneycomb-structured gold nanoparticle films with changeablepore morphology: from circle to ellipse. Langmuir 2005;21(5):2017–21.

[102] Ma HM, Hao JC. Evaporation-induced ordered honeycombstructures of gold nanoparticles at the air/water interface. Chem– Eur J 2010;16(2):655–60.

[103] Jiang XL, Zhou XF, Zhang Y, Zhang TZ, Guo ZR, Gu N. Interfacialeffects of in situ-synthesized Ag nanoparticles on breath figures.Langmuir 2010;26(4):2477–83.

[104] Wang J, Wang CF, Shen HX, Chen S. Quantum-dot-embeddedionomer-derived films with ordered honeycomb structures viabreath figures. Chem Commun 2010;46(39):7376–8.

[105] Li XF, Zhang LA, Wang YX, Yang XL, Zhao N, Zhang XL, et al. Abottom-up approach to fabricate patterned surfaces withasymmetrical TiO(2) microparticles trapped in the holes ofhoneycomb like polymer film. J Am Chem Soc 2011;133(11):3736–9.

[106] Kon K, Brauer CN, Hidaka K, Lohmannsroben HG, Karthaus O.Preparation of patterned zinc oxide films by breath figuretemplating. Langmuir 2010;26(14):12173–6.

[107] Zhao HJ, Shen YM, Zhang SQ, Zhang HM. A vapor phasehydrothermal modification method converting a honeycombstructured hybrid film into photoactive TiO2 film. Langmuir2009;25(18):11032–7.

[108] Li L, Li JA, Zhong YW, Chen CK, Ben Y, Gong JL, et al. Formationof ceramic microstructures: honeycomb patterned polymer filmsas structure-directing agent. J Mater Chem 2010;20(26):5446–53.

[109] Li L, Zhong YW, Ma CY, Li J, Chen CK, Zhang AJ, et al. Honeycomb-patterned hybrid films and their template applications via atunable amphiphilic block polymer/inorganic precursor system.Chem Mater 2009;21(20):4977–83.

[110] Ma CY, Zhong YW, Li J, Chen CK, Gong JL, Xie SY, et al. Patternedcarbon nanotubes with adjustable array: a functional breath figureapproach. Chem Mater 2010;22(7):2367–74.

[111] Ke BB, Wan LS, Chen PC, Zhang LY, Xu ZK. Tunable assembly ofnanoparticles on patterned porous film. Langmuir 2010;26(20):15982–8.

[112] Galeotti F, Mroz W, Bolognesi A. CdTe nanocrystal assembliesguided by breath figure templates. Soft Matter 2011;7(8):3832–6.

[113] Yabu H, Hirai Y, Shimomura M. Electroless plating of honeycomband pincushion polymer films prepared by self-organization.Langmuir 2006;22(23):9760–4.

[114] Hirai Y, Yabu H, Shimomura M. Electroless deposition of zinc oxideon pincushion films prepared by self-organization. Colloids Surf2008;313:312–5.

[115] Hirai Y, Yabu H, Matsuo Y, Ijiro K, Shimomura M. Arrays oftriangular shaped pincushions for SERS substrates prepared byusing self-organization and vapor deposition. Chem Commun2010;46(13):2298–300.

[116] You B, Shi L, Wen NG, Liu XH, Wu LM, Zi J. A facile method forfabrication of ordered porous polymer films. Macromolecules2008;41(18):6624–6.

[117] You B, Wen NG, Zhou SX, Wu LM, Zhao DY. Facile method forfabrication of nanocomposite films with an ordered porous surface.J Phys Chem B 2008;112(26):7706–12.

[118] Bolognesi A, Galeotti F, Giovanella U, Bertini F, Yunus S. Nanophaseseparation in polystyrene-polyfluorene block copolymers thin filmsprepared through the breath figure procedure. Langmuir2009;25(9):5333–8.

[119] Connal LA, Franks GV, Qiao GG. Photochromic, metal-absorbinghoneycomb structures. Langmuir 2010;26(13):10397–400.

[120] Galeotti F, Calabrese V, Cavazzini M, Quici S, Poleunis C, Yunus S,et al. Self-functionalizing polymer film surfaces assisted by specificpolystyrene end-tagging. Chem Mater 2010;22(9):2764–9.

[121] Tang PQ, Hao JC. Photoluminescent honeycomb films templated bymicrowater droplets. Langmuir 2010;26(6):3843–7.

[122] Munoz-Bonilla A, Ibarboure E, Bordege V, Fernandez-Garcia M,Rodriguez-Hernandez J. Fabrication of honeycomb-structuredporous surfaces decorated with glycopolymers. Langmuir2010;26(11):8552–8.

[123] Kojima M, Yabu H, Shimomura M. Direct observation of dye-containing amphiphilic copolymer in the honeycomb-patternedfilm. Macromol Symp 2008;267:109–12.

[124] Hsu JC, Sugiyama K, Chiu YC, Hirao A, Chen WC. Synthesis of newstar-shaped polymers with styrene-fluorene conjugated moietiesand their multicolor luminescent ordered microporous films.Macromolecules 2010;43(17):7151–8.

[125] Chiu YC, Kuo CC, Lin CJ, Chen WC. Highly ordered luminescentmicroporous films prepared from crystalline conjugated rod–coildiblock copolymers of PF-b-PSA and their superhydrophobiccharacteristics. Soft Matter 2011;7(19):9350–8.

[126] Ting SRS, Min EH, Escale P, Save M, Billon L, Stenzel MH. Lectinrecognizable biomaterials synthesized via nitroxide-mediatedpolymerization of a methacryloyl galactose monomer.Macromolecules 2009;42(24):9422–34.

[127] Yunus S, Delcorte A, Poleunis C, Bertrand P, Bolognesi A, Botta C. Aroute to self-organized honeycomb microstructured polystyrenefilms and their chemical characterization by ToF-SIMS imaging.Adv Funct Mater 2007;17(7):1079–84.

[128] Hernandez-Guerrero M, Min E, Barner-Kowollik C, Muller AHE,Stenzel MH. Grafting thermoresponsive polymers onto honeycombstructured porous films using the RAFT process. J Mater Chem2008;18(39):4718–30.

[129] Tanaka M, Takebayashi M, Shimomura M. Fabrication of orderedarrays of biodegradable polymer pincushions using self-orga-nized honeycomb-patterned films. Macromol Symp 2009;279:175–82.

[130] Tanaka M. Design of novel 2D and 3D biointerfaces using self-organization to control cell behavior. Biochim Biophys Acta – GenSubj 2011;1810(3):251–8.

[131] Uraki Y, Tamai Y, Hirai T, Koda K, Yabu H, Shimomura M.Fabrication of honeycomb-patterned cellulose material thatmimics wood cell wall formation processes. Mater Sci Eng C –Mater Biol Appl 2011;31(6):1201–8.

[132] Zhu YD, Sheng RL, Luo T, Li H, Sun JJ, Chen SD, et al. Honeycomb-structured films by multifunctional amphiphilic biodegradablecopolymers: surface morphology control and biomedicalapplication as scaffolds for cell growth. ACS Appl Mater Interfaces2011;3(7):2487–95.

[133] Liu WY, Liu RG, Li YX, Wang W, Ma L, Wu M, et al. Self-organizedordered microporous thin films from grafting copolymers. Polymer2009;50(12):2716–26.

[134] Ke BB, Wan LS, Zhang WX, Xu ZK. Controlled synthesis of linear andcomb-like glycopolymers for preparation of honeycomb-patternedfilms. Polymer 2010;51(10):2168–76.

[135] Min E, Wong KH, Stenzel MH. Microwells with patterned proteinsby a self-assembly process using honeycomb-structured porousfilms. Adv Mater 2008;20(18):3550–60.

[136] Li L, Chen CK, Li J, Zhang AJ, Liu XY, Xu B, et al. Robust andhydrophilic polymeric films with honeycomb pattern and their cellscaffold applications. J Mater Chem 2009;19(18):2789–96.

[137] Nystrom D, Malmstrom E, Hult A, Blakey I, Boyer C, Davis TP, et al.Biomimetic surface modification of honeycomb films via a‘‘Grafting From’’ approach. Langmuir 2010;26(15):12748–54.

[138] Ke BB, Wan LS, Xu ZK. Controllable construction of carbohydratemicroarrays by site-directed grafting on self-organized porousfilms. Langmuir 2010;26(11):8946–52.

[139] Chen P-C, Wan L-S, Ke B-B, Xu Z-K. Honeycomb-patterned filmsegregated with phenylboronic acid for glucose sensing. Langmuir2011;27(20):12597–605.

[140] Zhang WX, Wan LS, Meng XL, Li JW, Ke BB, Chen PC, et al.Macroporous, protein-containing films cast from water-in-oilemulsions featuring a block-copolymer. Soft Matter 2011;7(9):4221–7.

[141] Cui L, Han YC. Honeycomb pattern formation via polystyrene/poly(2-vinylpyridine) phase separation. Langmuir 2005;21(24):11085–91.

[142] Cui L, Li BY, Han YC. Transformation from ordered islands to holesin phase-separating P2VP/PS blend films by adding Triton X-100.Langmuir 2007;23(6):3349–54.

P. Escalé et al. / European Polymer Journal 48 (2012) 1001–1025 1025

[143] Cui L, Peng J, Ding Y, Li X, Han YC. Ordered porous polymer films viaphase separation in humidity environment. Polymer 2005;46(14):5334–40.

[144] Cui L, Wang HF, Ding Y, Han YC. Tunable ordered droplets inducedby convection in phase-separating P2VP/PS blend film. Polymer2004;45(24):8139–46.

[145] Cui L, Xuan Y, Li X, Ding Y, Li BY, Han YC. Polymer surfaces withreversibly switchable ordered morphology. Langmuir 2005;21(25):11696–703.

[146] Yabu H, Hirai Y, Kojima M, Shimomura M. Simple fabrication ofhoneycomb- and pincushion-structured films containingthermoresponsive polymers and their surface wettability. ChemMater 2009;21(9):1787–9.

[147] Yabu H, Shimomura M. Single-step fabrication of transparentsuperhydrophobic porous polymer films. Chem Mater2005;17(21):5231–4.

[148] Zander NE, Orticki JA, Karikari AS, Long TE, Rawlett AM. Super-hydrophobic surfaces via micrometer-scale templated pillars.Chem Mater 2007;19(25):6145–9.

Pierre Escalé is currently in Ph.D. (2009–2012) in polymeric chemistry under thesupervision of Pr. Laurent Billon, Dr. LaurentRubatat and Dr. Maud Save to develop hier-archically structured porous polymer films.He obtained his Licence and Master Degreesfrom the University of Pau (France) in 2007and 2009. After a training session in ArkemaCompany during his Licence Degree inChemistry, Pierre Escalé started in the field ofPolymer Chemistry in the Equipe de Physiqueet Chimie des Polymères in Pau during his

Master Degree. In 2009, he joined the group of Pr. Martina Stenzel at theCentre for Advanced Macromolecular Design, University of New SouthWales, Sydney (Australia) for a collaborative research on the synthesis

and self-assembly of glycopolymer by controlled radical polymerization(CRP). He also worked in collaboration with Pr. Filip Duprez at the Poly-mer Chemistry Research Group, University of Ghent (Belgium) in 2011.His researches mainly focused on the preparation of well-definedcopolymers by living/controlled radical polymerization techniques andthe characterization of their self-assembly at different scales by micros-copy or scattering techniques.

Dr. Laurent Rubatat is currently AssistantProfessor in the polymer group at the Uni-versity of Pau (UPPA) in France, since 2007.Laurent Rubatat studied Physics at GrenobleUniversity (UJF), and obtained his Ph.D. in2003 at the French Atomic Energy Commis-sion (CEA-Grenoble) from UJF. Followingpostdoctoral research in Soft Matter Physics atSimon Fraser University in Vancouver, Can-ada, he joined in 2006 the University of Frei-burg, Switzerland, Soft Matter Group as aDoctor Assistant. His research interest focuses

on the relationship between the multi-scale morphology of soft matterand its properties, such as ion and electron conductivities, rheology,

adhesion and wettability. Ongoing researches at UPPA address the controlof hierarchical structuring of polymer films using block copolymers self-assembly.

Prof. Laurent Billon received M.S. from theUniversity of Bordeaux (1992) where heworked on anionic ring opening polymeriza-tion of cyclosilazanes. He obtained his Ph.D.on synthesis of functional telechelic polyi-mides in 1996 at the University of Pau (UPPA).Subsequent to postdoctoral research for Rho-dia/Schlumberger on electro-rheologicalpolyzwitterionic fluids (1998) and ArkemaUSA on acrylic-modified fluoro-polymers byseeded emulsion (1999), he started his careeras Associate Professor in 2000 at the UPPA

where he earned the position of Full Professor in 2010. His researchinterest focuses on the design of well-defined polymer structures, espe-cially block and gradient copolymers, by controlled radical polymeriza-

tion techniques. His research activity is also focused on the developmentof Surface Initiated Nitroxide Mediated Polymerization to design func-tional hybrid colloidal particles and pigments with industrial partners. Aspecial attention concerns the self-organized nano/micron structures,such as colloidal crystal, inverse opal or honeycomb patterns, for photonicand responsive surfaces.

Dr. Maud Save is currently CNRS researcher inthe group of polymer (Equipe de Physique etChimie des Polymères) at the University ofPau (UPPA) in France. Maud Save obtained herHabilitation in 2011. She started her academiccareer in 1996 in the Laboratoire de Chimiedes Polymères Organique (France). Herresearch work focused on the ring openingpolymerization of cyclic esters initiated byrare earth derivatives. She received her Ph.D.in 2000 from the University of Bordeaux. In2001, she moved to the University of Sussex in

Brighton (UK) to join the group of Prof. Steve P. Armes for a post-doctoralresearch on the synthesis of amphiphilic copolymers by ATRP and self-assembly into cross-linked micelles. She spent one year at the School of

Engineering of Chemistry at Nancy (ENSIC, France) for a lecturer positionwhere she was interested in the synthesis of graft amphiphilic polymersbased on dextran. In 2002, she obtained a permanent researcher positionat CNRS in the Laboratoire de Chimie des Polymères, University Paris VI(France). During five years, the research program developed in the groupof Prof. Bernadette Charleux was focused on controlled radical polymer-ization either applied in aqueous dispersed media or used for the elabo-ration of hybrid organic-inorganic materials. Her research activities arefocused on the synthesis of macromolecular architectures (block, gradi-ent, branched star copolymer, polymer brushes) synthesized by con-trolled radical polymerization to design functional surfaces, colloïds orhybrid particles.