Application of superhydrophobic sol gel on canvas

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/authorsrights

http://www.elsevier.com/authorsrights

Author's personal copy

Applied Surface Science 307 (2014) 101–108

Contents lists available at ScienceDirect

Applied Surface Science

jou rn al h om ep age: www.elsev ier .com/ locate /apsusc

Application of superhydrophobic sol gel on canvas

Shing Dar Wanga,∗, Bai Jun Lina, Chien Cheng Hsiehb, Chao Chieh Linb

a Institute of Materials Science, National Yunlin University of Science & Technology, 123, Sec 3, University Rd., Douliu, Yunlin, Taiwan, ROCb Taiwan Textile Research Institute Yunlin branch, ROC

a r t i c l e i n f o

Article history:Received 25 January 2014Received in revised form 11 March 2014Accepted 25 March 2014Available online 4 April 2014

Keywords:Superhydrophobic surfaceSelf-cleaningWater contact angleCanvasweatherability

a b s t r a c t

In this study, a superhydrophobic sol gel (SHSG) was used to promote self-cleaning ability of canvas.Four kinds of coating methods were studied and water impact test was used to assess the quality of thecoating. The scraper method rendered a relatively flat surface; and water contact angles (WCAs) of twobilayers polytetrafluoroethylene (PTFE)/SHSG-coated canvas were 153.3◦ ± 3.1◦ and 141.7◦ ± 3.3◦ beforeand after water impact of 2 h, respectively. SEM, energy dispersive x-ray spectrometry (EDX), and FTIRwere applied to characterize the PTFE/SHSG coating. Although SHSG was dropped on top of the PTFEfilm during sample preparation, the analysis of EDX and FTIR indicated that the chains of PTFE extendedupward and SHSG moved downward during the heat treatment with preheat. The combination of SHSGwith PTFE promoted not only hydrophobicity but also the strength and weatherability of the canvas.The tensile strength of a PTFE/SHSG-coated canvas was always superior to a PTFE-coated canvas duringaccelerated weathering test. After accelerated weathering test of 300 h, the two bilayers PTFE/SHSG-coated canvas had a tensile strength of 237 kg, static WCA of 143.7◦ ± 2.1◦, a contact angle hysteresis of8◦, and a sliding angle of 4◦, which represented an outstanding self-cleaning ability.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

The application of nanotechnology to the traditional tex-tile industry, including natural, artificial or synthetic fibers, hasattracted considerable interest in recent years [1–20]. Due to theextraordinary photocatalytic activity, non-toxicity, high availabil-ity, biocompatibility, and low price, TiO2 nanoparticles have beenapplied extensively onto textile materials to obtain UV-protecting,self-cleaning, superhydrophobic or superhydrophilic as well asanti-bacterial properties [1–4]. Nitrogen doped TiO2-cotton fab-rics or TiO2 combined with different metals ions (Fe, Co, Zn, andAg) cotton fabrics showed significant photocatalytic activity in thedegradation of methylene blue or methyl orange under visible-lightirradiation [2–4]. Since silver or silver ions are effective againstmany disease-causing organisms in the body, and relatively non-toxic for human cells, silver nanoparticles are widely applied ontotextile materials to impart antibacterial ability [5–8].

Silica sol has been used by many researchers to producesuperhydrophobic textiles [6–14]. The abundant hydroxyl groupson the cotton fiber surface favor upload and attachment ofhydrolyzed SiO2 nanoparticles on the surface. The roughness, attwo levels (micro- and nanoscales), enabling trapping of air under

∗ Corresponding author. Tel.: +886 5 5342601x3411; fax: +886 5 532 1719.E-mail address: [email protected] (S.D. Wang).

water droplets can be obtained through adequate condensation ofhydrolyzed SiO2 sol. The low surface energy characteristic can beachieved by the modification of sol gel with a long chain alkyl silaneor fluorochemicals. ZnO nanorod arrays or nanoparticles, due totheir antibacterial properties and cost-effectiveness compared tosilver nanoparticles, have also been created on cotton substratesand subsequent hydrophobic modification with a long chain alkylsilane, fluoride or stearic acid [15–19]. Since the surface tensionof oil, such as hexadecane 27.5 mN/m, is lower than that of water(72.1 mN/m), the superhydrophobic surface is also superoleophilic.This characteristic can be used in fabrication of superhydropho-bic and superoleophilic textiles for the treatment of increasingindustrial oily wastewater and polluted oceanic water, as well asthe frequently occurring accidental oil spills [11–13,15,18,20]. Xueet al. [11] used tetraethoxysilicate (TEOS), 1,1,1,3,3,3-hexamethyldisilazane (HMDS), n-hexane, ammonia solution, hydrochloric acid(HCl) to fabricate superhydrophobic and superoleophilic textilesfor oil–water separation. However, n-hexane can cause neurop-athy. A superhydrophobic and oleophilic sol–gel nanocompositecoating with oil contact angle of <10◦ will improve oleophobic prop-erty through the further lowering of surface energy by the presenceof a fluorochemical [21,22].

Fluorochemicals have been employed for hydrophobic andoleophobic surface modifications in many of the reported works[10,14,15,21–23]. However, most fluorinated materials may causeserious risks to human health upon coming in contact with skin.

http://dx.doi.org/10.1016/j.apsusc.2014.03.1730169-4332/© 2014 Elsevier B.V. All rights reserved.


102 S.D. Wang et al. / Applied Surface Science 307 (2014) 101–108

In addition to fluoride, several other chemicals are also used in thefabrication of the above mentioned functional textiles. It has notbeen investigated extensively if these textiles trigger any allergyupon skin contact. However, this may not be a case for a super-hydrophobic canvas since it does not come in contact with humanbody upon use.

Canvas is used as the substrate of an oil painting. The applicationof polar organic solvents as cleaning tools for painting surfaces isstill a widely adopted technique. Unfortunately, the capillary pen-etration of a liquid into the paint layers can lead to swelling andleaching of the original organic components (mainly varnishes andbinding media) constituting the layered paint structure [24]. Deiet al. [25] developed a new approach with gels which was intendedto minimize the time necessary to achieve the desired cleaningaction, and then removed the gel by converting it to a low-viscosityfluid in situ by a rapid, mild chemical perturbation. Instead of usinggel with liquid cleaning agents, a superhydrophobic and super-oleophilic coating can impart the canvas a self-cleaning property.

Canvas is widely used in outdoor pavilions, awnings, multi-purpose sports complexes, huge span tension membrane roofs,tents, etc. To provide a comfortable environment for users, it mustpossess properties of durability, inertness, cleanability, and easy-care attributes. It should function as a self-cleaning system; andairborne dirt should be automatically washed off by rain. Afterextended periods of outdoor exposure, it should retain a highdegree of flexibility and strength. Nevertheless, the research aboutself-cleaning of canvas is very rare.

This work investigated the application of superhydrophobicsol gel (SHSG) on canvas. The SHSG was synthesized from TEOS,HMDS, HCl, and ethanol. Therefore, it is fluorine free. The opti-mal method of applying SHSG and polytetrafluoroethylene (PTFE)simultaneously on the canvas was studied systemically. Waterimpact test for 2 h was used to assess the endurance of the coat-ing. Contact angle tester was used to determine the water contactangle (WCA) before and after water impact test. Scanning elec-tron microscopy (SEM) and energy dispersive x-ray spectrometry(EDX) were used to analyze the variation of surface morphologyand distribution of SHSG and PTFE in the coating. The 3D surfacemorphologies of the films were investigated using an atomic forcemicroscope (AFM). Fourier transform infrared spectroscopy (FTIR)was used to identify chemical bonding between molecules in thecoating. Tensile test was conducted to determine the effect of sol geladdition on the strength of the canvas. Accelerated weathering testwas performed to estimate the weatherability of the PTFE/SHSG-coated canvas.

2. Experimental

2.1. Materials

PTFE powder of 300 nm was purchased from DU PONT. Fluo-rine surfactant S420 was purchased from AGC SEIMI CHEMICALCO. The PTFE emulsion with model number Zewffl Gk570 was pur-chased from TAIWAN DAIKIN ADVANCED CHEMICALS. The maincomponent of this PTFE emulsion is PTFE. The diameter of fiberglass yarn is 4 �m. Fiber glass yarns are weaved into a fiberglasscloth with a density of 24 strips of fiberglass yarns in both ver-tical and horizontal directions. The mass density of the fiberglasscloth is 450 g/m2. The commercial canvas with PTFE membrane waspurchased from Chukoh Chemical Industries (Japan) with modelnumber of FGT-600.

2.2. Sample preparation

SHSG with tri-methyl-modified silica sol was synthesizedthrough the reaction of hexamethyldisilazane (HMDS) and

hydrolyzed tetraethoxysilane (TEOS) as described in detail else-where [26,27]. Four kinds of samples were prepared in this study.

Sample A:SHSG, aged for 7 days, was deposited on the commercial canvas

through a dropper and then heat treated at 200 ◦C for 2 h.Sample B:PTFE powder, fluorine surfactant S420, and SHSG in mass ratios

of 1:1:1, 1:2:2, and 1:2:4 were stirred uniformly using a homoge-nizer, deposited on the fiberglass cloth through a dropper and thenheat treated at 200 ◦C for 2 h.

Sample C:Fiberglass cloth was dipped into PTFE emulsion (Zewffl Gk570

Taiwan Daikin) and then lifted to coat with SHSG by a dropper. Afterheat treatment at 200 ◦C or 300 ◦C for 2 h, one bilayer of PTFE/SHSGwas obtained. One, two, three or five bilayers of PTFE/SHSG werecoated on the fiberglass cloth.

Sample D:The scraper with four blades was used and film thicknesses of 30,

60, 90 or 120 �m were scraped out by the four blades, respectively.The fiberglass cloth was dipped into PTFE emulsion (Zewffl Gk570Taiwan Daikin). A film thickness of 30 �m was scraped out by thescraper. The SHSG was dropped onto the PTFE film. A film thick-ness of 60 �m, containing PTFE and SHSG, was scraped out by thescraper. After heat treatment at 200 ◦C or 300 ◦C for 2 h, one bilayerof PTFE/SHSG was completed. The total thicknesses of two and threebilayers of PTFE/SHSG were 120 and 180 �m, respectively.

The fiberglass cloth coated with PTFE and SHSG of samples B, Cand D are designated as PTFE/SHSG-coated canvas.

2.3. Sample tests

2.3.1. Water impact testIn order to estimate the rain shock endurance of all the samples,

a water column with cross sectional area of 1.7 cm2 was impactedon the samples from a height of 45.5 cm for 2 h. Water impact veloc-ity was estimated to be about 2.99 m/s, and WCA was measured.

2.3.2. Tensile testSamples of 40 × 150 mm were subjected to tensile strength mea-

surements by the 8801 servohydraulic testing system of InstronEngineering Corporation. The tensile test machine worked at a rateof 100 mm/min with the initial distance between the clamps equalto 110 mm. Maximum load at break was determined for sampleswith different processing conditions.

2.3.3. Accelerated weathering testThe samples were mounted in a Global UV testing chamber

(Ci4000 Xenon Arc Weather-Ometer, ATLAS, USA) by means ofa custom-made sample holder. According to test program of ISO4892-2, the test conditions included ultraviolet irradiation of wave-length of 300–400 nm with intensity of 60 W/m2, black paneltemperature of 65 ◦C, chamber temperature of 38 ◦C, and relativehumidity of 50%. WCA of the samples was measured for every50 h, and tensile test was conducted for every 100 h of acceleratedweathering test.

2.4. Characterization of PTFE/SHSG coating

The WCA of all the samples, determined using a contact angletester, was an average of three independent measurements foreach sample. Advancing contact angle measurements were per-formed by adding liquid to the water droplets, and receding contactangle measurements were made by removing liquid from the drops.The sliding angle was defined as the smallest tilted angle � of thePTFE/SHSG-coated canvas at which the deposited water dropletsslid off immediately after dispensing from a needle.


S.D. Wang et al. / Applied Surface Science 307 (2014) 101–108 103

Table 1Variations in WCA due to water impact test for sample C.

Number of bilayer Heat treatmenttemperature (◦C)

WCA before waterimpact (◦)

Period of waterimpact (min)

WCA after waterimpact (◦)

1 200 151.3 ± 1.6 10 105.0 ± 9.4300 138.3 ± 1.6 10 94.3 ± 2.4

2 200 153.6 ± 2.6 120 135.3 ± 3.8300 144.7 ± 5.4 120 131.3 ± 6.4

3 200 154.3 ± 1.8 120 141.7 ± 6.2300 142.3 ± 6.2 120 130.3 ± 1.2

5 200 139.3 ± 2.4 120 134.7 ± 4.3300 135.6 ± 1.5 120 128.7 ± 3.5

Table 2Variations in WCA due to water impact test for sample D.

Number of bilayer Heat treatmenttemperature (◦C)

WCA beforewater impact (◦)

Period of waterimpact (min)

WCA after waterimpact (◦)

1 200 146.0 ± 2.2 35 108.0 ± 6.5300 142.0 ± 2.2 35 106.3 ± 5.8

2 200 153.3 ± 3.1 120 141.7 ± 3.3300 150.7 ± 2.1 120 137.3 ± 3.6

3 200 152.3 ± 2.1 120 139.0 ± 1.7300 151.7 ± 1.7 120 139.3 ± 2.3

SEM was used to analyze the morphology of PTFE/SHSG coating,and EDX was used for surface elemental analysis. The 3D surfacemorphology and root-mean-square (RMS) roughness of the filmswere investigated using an AFM (Dimension D3100S-1) in tappingmode.

The bonding and distribution of PTFE and SHSG in the sam-ples were analyzed by attenuated total reflection Fourier transforminfrared (ATR-FTIR) spectroscopy (TENSOR 27 FTIR/HYPERION1000, Bruker Optics) with 32 scans at a resolution of 4 cm−1. Trans-mission FTIR spectroscopy using KBr pellets with 64 scans at aresolution of 4 cm−1 was also adopted to investigate hydrophobicbonding of SHSG.

3. Results and discussion

3.1. Water impact test

Variations in WCA due to water impact test for samples A, B, C,and D are summarized in Tables 1–3, and Table S4 of SupplementaryMaterial, respectively.

3.1.1. Water impact test of sample A:After deposition of SHSG, WCA of the commercial canvas

was enhanced from 90.7◦ ± 4.0◦ to 144.3◦ ± 4.2◦ (Table S1 ofSupplementary Material), but it decreased to 86.7◦ ± 2.1◦ afterwater impact for 15 min. These results indicated that there was

Table 3The effect of addition or omission of additional ethanol at molar ratio 6 after thecompletion of adding process of HMDS during the preparation process of SHSG onthe tensile strength of the two bilayers PTFE/SHSG-coated canvas.

Aging periodof SHSG (day)

Additional ethanolat molar ratio 6

Heating method Tensilestrength (kg)

7 Addition Without preheat 2467 Addition With preheat 263

11 Addition Without preheat 25711 Addition With preheat 27616 Addition Without preheat 27216 Addition With preheat 29080 Addition With preheat 243

7 Omission Without preheat 2687 Omission With preheat 274

11 Omission Without preheat 28111 Omission With preheat 294

no bonding between SHSG and the commercial canvas. SHSG wasonly physically adsorbed on the canvas, so it could not resist theimpact of water.

3.1.2. Water impact test of sample B:When PTFE powder, fluorine surfactant S420, and SHSG were

used in ratio of 1:2:4, WCA increased to 144.0◦ ± 2.9◦ after heattreatment and decreased to 88.0◦ ± 2.6◦ after water impact for10 min (Table S2 of Supplementary Material). On the other hand, ata ratio of 1:1:1, WCA was only 136.3◦ ± 1.2◦ after heat treatmentand even remained 104.3◦ ± 2.5◦ after water impact for 40 min.These results implied that when SHSG/PTFE > 1, samples had highinitial WCA, but PTFE could not seize excessive SHSG, hence WCAdecreased abruptly after the water impact. When SHSG/PTFE ≤ 1,PTFE was better able to grasp the SHSG, the sample showed betterwater impact endurance but a lower WCA.

3.1.3. Water impact test of sample C:With single bilayer of PTFE/SHSG, WCA increased to

151.3◦ ± 1.6◦ but decreased to 105.0◦ ± 9.4◦ after water impactfor only 10 min (Table 1). Five bilayers of PTFE/SHSG resulted inWCA drop only by 3.6% after water impact for 120 min. Never-theless, WCA of 139.3◦ ± 2.4◦ did not satisfy superhydrophobiccondition. With two (three) bilayers of PTFE/SHSG, the initialWCA of 153.6◦ ± 2.6◦ (154.3◦ ± 1.8◦), met the superhydrophobiccondition and WCA reduced by 12% (9%) after a water impact for120 min. However, the coating surface was not flat due to the lackof thickness control as shown in Fig. 1.

3.1.4. Water impact test of sample D:WCAs of the coatings with a heat treatment at 200 ◦C were

all higher than the corresponding coatings with a heat treatmentat 300 ◦C regardless the number of bilayers (Table 2). With onebilayer of PTFE/SHSG, WCA dropped by ∼26% after water impact for35 min. With two and three bilayers of PTFE/SHSG, WCA reachedto 153.3◦ ± 3.1◦ and 152.3◦ ± 2.1◦, and retained at 141.7◦ ± 3.3◦ and139.0◦ ± 1.7◦, respectively, after a water impact for 120 min. Theresults, shown in Tables 1 and 2, indicated that at least two bilayersof PTFE/SHSG were essential to resist water impact. Furthermore,the coating surface of sample D obtained by scraper method (Fig. 2)was flatter than that of sample C obtained by dip-drop method(Fig. 1). Therefore, sample D and scraper method were used in thefollowing tests and analyses.



Fig. 1. A water drop on the surface of sample C with WCA of 156.8◦ .

3.2. Tensile test

Ethanol and water condensation continued to occur after thepreparation process of sol gel. Aging period influenced the threedimensional structure and magnitude of the sol gel particles. Afterthe completion of adding process of HMDS, one more addition ofethanol at molar ratio 6 (ethanol/TEOS = 6) to the sol can reducethe degree of condensation and promote the transmittance of thefilm spin-coated from the sol gel [27]. But coating of high transmit-tance is not required for canvas. The effect of addition or omissionof additional ethanol at molar ratio 6 after the completion of addingprocess of HMDS on the tensile strength was compared and is pre-sented in Table 3. One more addition of ethanol at molar ratio 6 afterthe addition of HMDS enhanced the tensile strength of PTFE/SHSG-coated canvas with increasing aging period of sol gel and reacheda maximum of 290 kg with sol gel aged for 16 days. Sol gel agedfor 80 days resulted in large particles which could not be mixeduniformly with PTFE resulting in a lower tensile strength (243 kg).The tensile strength of PTFE/SHSG-coated canvas with sol gel, withone more addition of ethanol at molar ratio 6 after the addition ofHMDS, aged for 11 and 16 days (276 and 290 kg) were almost equalto PTFE/SHSG-coated canvas with sol gel, without one more addi-tion of ethanol at molar ratio 6 after the addition of HMDS, agedfor 7 and 11 days (274 and 294 kg), respectively. Consequently, forfiberglass cloth to coat with PTFE/SHSG, no additional ethanol wasrequired at the end of HMDS addition during the preparation pro-cess of SHSG. The effect of heating method on the tensile strength ofPTFE/SHSG-coated canvas is also summarized in Table 3. The ten-sile strength of PTFE/SHSG-coated canvas with heating from roomtemperature to 200 ◦C after scraper coating was always larger thanthat of PTFE/SHSG-coated canvas when heated at 200 ◦C but with-out preheat after scraper coating. As the PTFE/SHSG coating washeated at 200 ◦C but without preheat, the ethanol in the coatingevaporated violently and SHSG solidified quickly. In this situation,SHSG did not have sufficient time to cross link with PTFE beforesolidification. SHSG and PTFE were more inclined to separate fromeach other rendering the PTFE/SHSG-coated canvas with a lowertensile strength.

3.3. Accelerated weathering test

The two bilayers PTFE/SHSG-coated canvas of sample D withheat treatment at 200 ◦C were tested for accelerated weathering todetermine the variation of WCA and tensile strength at outdoors.Additionally, samples designated as PTFE-coated canvas, for whichthe fiberglass cloth was dipped into the PTFE emulsion (ZewfflGk570 Taiwan Daikin) and a film thickness of 120 �m was scrapedout by the scraper with heat treatment at 200 ◦C, were prepared forcomparison. The original tensile strength of a PTFE/SHSG-coatedcanvas (288 Kg) was stronger than a PTFE-coated canvas (256 Kg).The tensile strength of both PTFE/SHSG and PTFE-coated canvasdecreased with the increasing hours of accelerated weatheringtest, but the strength of the former was always superior to thelatter during 300 h of accelerated weathering test (Table S3 of Sup-plementary Material). Therefore, the combination of SHSG withPTFE not only increased WCA of the canvas but also promotedthe strength and weatherability of the canvas. During the 300 h ofaccelerated weathering test, WCA of the PTFE/SHSG-coated canvasdecreased slowly from 153.3◦ ± 2.1◦ to 143.7◦ ± 2.1◦ (Table S4 ofSupplementary Material), which was lower than 150.0◦. Neverthe-less, the contact angle hysteresis of the PTFE/SHSG-coated canvaswas still as low as 8.0◦ even after 300 h of accelerated weatheringtest. The sliding angles of two bilayers PTFE/SHSG-coated canvasof sample D were 3◦ and 4◦, for just prepared and after acceleratedweathering test of 300 h, respectively (see Video). Consequently,the PTFE/SHSG-coated canvas of sample D exhibited an outstandingself-cleaning ability.

3.4. SEM, EDX and AFM analyses

Since SHSG is tri-methyl-modified silica sol and the formula ofPTFE is (C2F4)n, therefore the signal of Si atom appearing in the EDXanalysis of the coating was equivalent to the detection of SHSG inthe coating. It is clear from the EDX analysis of the three bilay-ers coating (Fig. 3(c)) that the sheet in the coating was composedof PTFE and SHSG, and only PTFE but no SHSG appeared in thecrack between the sheets. A large area in one bilayer coating of

Fig. 2. A water drop on the surface of sample D with WCA of 156.4◦ .



Fig. 3. Photographs of SEM and EDX analysis of (a) one bilayer, (b) two bilayers, and (c) three bilayers PTFE/SHSG-coated canvas of sample D.

PTFE/SHSG contained only PTFE (Fig. 3(a)), this was the area firstlycorroded by water during the water impact and this can explainwhy one bilayer PTFE/SHSG-coated canvas of sample C and D hadpoor water impact endurance (Tables 1 and 2). When the coating ofPTFE/SHSG was two bilayers, the sheet structure covered the wholecoating surface (Fig. 3(b)). Consequently, WCA of the coatings, justafter heat treatment, met with the superhydrophobic condition anddecreased only ∼7% after a water impact for 2 h. In case of coat-ing of PTFE/SHSG with three bilayers, the area of one sheet in thecoating was obviously larger than that in the two bilayers coating.This meant that PTFE and SHSG were more uniformly distributedin the coating of three bilayers than in the coating of two bilayers.Therefore, WCA of the three bilayers coatings, just after heat treat-ment, also met with the superhydrophobic condition. It still kept∼139o even after water impact for 2 h, and had a smaller standarddeviation than that of two bilayers coating.

The atomic percentages of F and Si in EDX analysis wereworth paying attention (Fig. 3(b) and (c)). F/Si was 58.35/5.11 and49.99/3.99 at the two regions of a two bilayers PTFE/SHSG coatingand was 30.66/11.2 in a large sheet of a three bilayer PTFE/SHSGcoating. The SHSG was dropped onto the PTFE film in the samplepreparation of sample D. Both the PTFE film and SHSG film in a sin-gle bilayer, scraped out separately by the scraper, had a thicknessof 30 �m, and the SHSG film was on top of the PTFE film beforethe heat treatment. F/Si ratios of two bilayers PTFE/SHSG coatingand three bilayers PTFE/SHSG coating indicated that PTFE movedupward and SHSG moved downward during the heat treatment.

Fig. 4(a and b) show 3D surface morphologies of the two bilay-ers PTFE/SHSG-coated canvas of sample D with RMS roughness of197.63 nm and a PTFE-coated canvas with the same film thicknessof 120 �m with RMS roughness of 40.30 nm. The surface of a PTFE-coated canvas was very flat compared to the steep topography ofthe two bilayers PTFE/SHSG-coated canvas.

Fig. 5 represents a picture of some water drops on a piece of twobilayers PTFE/SHSG-coated canvas showing excellent hydropho-bicity.

3.5. FTIR analysis

FTIR analysis was performed to understand why the best heattreatment temperature was 200 ◦C not 300 ◦C. SHSG was coated ona glass substrate and heat treated at 200 ◦C or 300 ◦C. The coatingwas scraped from the glass to incorporate in a thin KBr disk. Ethanolwas added during the preparation process of SHSG and was pro-duced in ethanol condensation. The strength of Si–O–Si stretchingand CH3 symmetric deformation of Si–CH3 [28] with heat treat-ment at 300 ◦C were weaker than those with heat treatment at200 ◦C (Fig. 6), it indicated that some of Si–O–Si and Si–CH3 bond-ing of SHSG was pyrolyzed with heat treatment at 300 ◦C. Therefore,SHSG had more hydrophobic bonds of –CH3 when heat treated at200 ◦C rather than at 300 ◦C.

Fig. 7 shows the ATR-FTIR spectra of a fiberglass cloth coatedwith (a) only PTFE; (b) only SHSG; and (c) two bilayers ofPTFE/SHSG. The strength of absorption peaks at 1205 cm−1 and



Fig. 4. AFM photograph of (a) the two bilayers PTFE/SHSG-coated canvas of sampleD; (b) a PTFE-coated canvas.

Fig. 5. A picture of some water drops on a piece of two bilayers PTFE/SHSG-coatedcanvas.

1160 cm−1 representing CF2 groups of PTFE were quite similar inPTFE/SHSG bilayer to as those in PTFE coating. As the siloxanechains became longer or branched, the Si–O–Si absorption becamebroader and more complex. Nevertheless, the absorption peaks at1256 cm−1 and 1071 cm−1, assigned as CH3 symmetric deformationof Si–CH3 and Si–O–Si stretching [28] respectively, of SHSG coatingdisappeared or became a weaker band (1087 cm−1) in PTFE/SHSGbilayer. It should be noted again that in the preparation of two bilay-ers PTFE/SHSG-coated canvas (sample D), the SHSG was droppedonto the PTFE film and then heat treated at 200 ◦C or 300 ◦C. There-fore, the infrared spectrum implies that PTFE extended upward andSHSG moved downward during the heat treatment. PTFE entan-gled and crosslinked with SHSG after solidification. The infraredbands of PTFE were more obvious than those of SHSG in the spec-trum of two bilayers of PTFE/SHSG at 1300 cm−1–1000 cm−1, whichmeans that PTFE has a large proportion in the penetration depth ofthe ATR measurements (1–2 �m). This conclusion agrees with thatof EDX analysis. The ATR and EDX analyses can also provide evi-dence of microstructure to explain the result of Table 3. PTFE chainand three dimensional extended structure of SHSG in PTFE/SHSGbilayer had enough time to interpenetrate and entangle with eachother as the PTFE/SHSG bilayer was heated at 200 ◦C with preheat,

Fig. 6. Transmission FTIR spectra of a superhydrophobic film spin-coated from SHSG. (a) Before heat treatment, heat treatment at (b) 200 ◦C, and (c) 300 ◦C.



Fig. 7. ATR-FTIR spectra of a glass fiber cloth coated with (a) only PTFE; (b) onlySHSG; and (c) two bilayers of PTFE/SHSG.

and such entangling would have hindered the free stretching ofPTFE chain as the PTFE/SHSG-coated canvas was tensioned. TheEDX, AFM and FTIR analyses indicated that SHSG provided theroughness and hydrophobic bonds of −CH3 needed for superhy-drophobicity, and PTFE provided CF2 groups in the coating nearestto the surface to resist the water impact. Therefore, the two bilay-ers PTFE/SHSG-coated canvas exhibited excellent water impactendurance and WCA of 153.0 ± 3.0◦, which is greatly significantthan WCA (91.0 ± 3.0◦) of the commercial canvas.

4. Conclusions

SHSG was applied to promote the hydrophobicity and self-cleaning ability of canvas. Four kinds of coating methods, including(1) dropping SHSG directly on a commercial canvas; (2) mixingPTFE powder, fluorine surfactant S420, and SHSG and then drop-ping on the fiberglass cloth; (3) dipping the fiberglass cloth intoPTFE emulsion (Zewffl Gk570 Taiwan Daikin) and then droppingthe SHSG onto the PTFE film; and (4) scrapping out every sub-layerof PTFE and SHSG by a scraper were studied in this work. Waterimpact endurance was used to find out the best coating method.At least two bilayers of PTFE/SHSG were needed to resist the waterimpact. WCAs of two and three bilayers of PTFE/SHSG-coated can-vas, obtained by scraper method and heat treatment at 200 ◦C, were153.3◦ ± 3.1◦, 152.3◦ ± 2.1◦ and 141.7◦ ± 3.3◦, 139.0◦ ± 1.7◦, beforeand after water impact of 2 h, respectively. The smaller standarddeviation of three bilayers coating corresponded to a larger areaof one single sheet, which contained more uniform distributionof PTFE and SHSG in the coating as revealed by SEM analysis.The tensile strength of PTFE/SHSG-coated canvas, with SHSG agedfor 11 days, could reach 294 kg. Sol gel with a too long aginghad too large particles which could not be mixed uniformly withPTFE that resulted in a lower tensile strength. Although SHSG wasdropped on the top of PTFE film, the analyses of EDX and ATRmeasurements indicated that the chains of PTFE extended upwardand SHSG moved downward as the PTFE/SHSG-coated canvas washeated from room temperature. This can be interpreted in termsof entangling of PTFE and SHSG that promotes tensile strengthof the PTFE/SHSG-coated canvas. SHSG provided the roughnessand hydrophobic bonds of –CH3 needed for superhydrophobicityand PTFE provided CF2 groups in the coating nearest to the sur-face to resist the water impact. Consequently, the combination of

SHSG with PTFE promoted not only self-cleaning ability but alsothe strength and weatherability of the canvas. The tensile strengthof PTFE/SHSG-coated canvas was always superior to that of PTFE-coated canvas during weathering test of 300 h. After acceleratedweathering test of 300 h, the two bilayers PTFE/SHSG-coated can-vas had a tensile strength of 237 kg, static WCA of 143.7◦ ± 2.1◦,a contact angle hysteresis of 8◦, and a sliding angle of 4◦, whichrepresented an outstanding self-cleaning ability.

Acknowledgement

The authors would like to thank the Taiwan Textile ResearchInstitute, Republic of China, for financially supporting this researchunder the project of “Research on the compatibility and physicalproperties of sol gel and fluorine resin”.

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.apsusc.2014.03.173.

References

[1] B. Tan, B. Gao, J. Guo, X. Guo, M. Long, A comparison of TiO2 coated self-cleaningcotton by the sols from peptizing and hydrothermal routes, Surf. Coat. Technol.232 (2013) 26.

[2] D. Wu, M. Long, Low-temperature synthesis of N-TiO2 sol and characterizationof N-TiO2 coating on cotton fabrics, Surf. Coat. Technol. 206 (2012) 3196.

[3] S. Afzal, W.A. Daoud, S.J. Langford, Visible-light self-cleaning cotton bymetalloporphyrin-sensitized photocatalysis, Appl. Surf. Sci. 275 (2013)36.

[4] D. Wu, L. Wang, X. Song, Y. Tan, Enhancing the visible-light-induced photo-catalytic activity of the self-cleaning TiO2-coated cotton by loading Ag/AgClnanoparticles, Thin Solid Films 540 (2013) 36.

[5] C. Srisitthiratkul, W. Yaipimai, V. Intasanta, Environmental remediation andsuperhydrophilicity of ultrafine antibacterial tungsten oxide-based nanofibersunder visible light source, Appl. Surf. Sci. 259 (2012) 349.

[6] A.A. Hebeish, M.M. Abdelhady, A.M. Youssef, TiO2 nanowire and TiO2 nanowiredoped Ag-PVP nanocomposite for antimicrobial and self-cleaning cotton tex-tile, Carbohyd. Polym. 91 (2013) 549.

[7] N. Radic, B.M. Obradovic, M. Kostic, B. Dojcinovic, M.M. Kuraica, M. Cernák,Deposition of silver ions onto DBD and DCSBD plasma treated nonwovenpolypropylene, Surf. Coat. Technol. 206 (2012) 5006.

[8] Y.H. Chen, C.C. Hsu, J.L. He, Antibacterial silver coating on poly(ethylene tereph-thalate) fabric by using high power impulse magnetron sputtering, Surf. Coat.Technol. 232 (2013) 868.

[9] S. Li, S. Zhang, X. Wang, Fabrication of Superhydrophobic Cellulose-Based Mate-rials through a Solution-Immersion Process, Langmuir 24 (2008) 5585.

[10] F. Ferrero, M. Periolatto, Application of fluorinated compounds to cotton fabricsvia sol–gel, Appl. Surf. Sci. 275 (2013) 201.

[11] C.H. Xue, P.T. Ji, P. Zhang, Y.R. Li, S.T. Jia, Fabrication of superhydrophobic andsuperoleophilic textiles for oil–water separation, Appl. Surf. Sci. 284 (2013)464.

[12] F. Liu, M. Ma, D. Zang, Z. Gao, C. Wang, Fabrication of superhydropho-bic/superoleophilic cottonfor application in the field of water/oil separation,Carbohyd. Polym. 103 (2014) 480.

[13] L. Wu, J. Zhang, B. Li, A. Wang, Mechanical- and oil-durable superhydropho-bic polyester materials for selective oil absorption and oil/water separation, J.Colloid. Interf. Sci. 413 (2014) 112.

[14] M. Zhang, S. Wang, C. Wang, J. Li, A facile method to fabricate superhydrophobiccotton fabrics, Appl. Surf. Sci. 261 (2012) 561.

[15] Y. Qing, Y. Zheng, C. Hu, Y. Wang, Y. He, Y. Gong, Q. Mo, Facile approach infabricating superhydrophobic ZnO/polystyrene nanocomposite coating, Appl.Surf. Sci. 285P (2013) 583.

[16] E. Richard, R.V. Lakshmi, S.T. Aruna, B.J. Basu, A simple cost-effective and eco-friendly wet chemical process for the fabrication of superhydrophobic cottonfabrics, Appl. Surf. Sci. 277 (2013) 302.

[17] M. Ashraf, C. Campagne, A. Perwuelz, P. Champagne, A. Leriche, C. Courtois,Development of superhydrophilic and superhydrophobic polyester fabric bygrowing Zinc Oxide nanorods, J. Colloid. Interf. Sci. 394 (2013) 545.

[18] M. Zhang, C. Wang, S. Wang, J. Li, Fabrication of superhydrophobic and super-oleophilic textiles for oil–water separation Fabrication of superhydrophobiccotton textiles for water–oil separation based on drop-coating route, Carbohyd.Polym. 97 (2013) 59.

[19] E.S. Ates, H.E. Unalan, Zinc oxide nanowire enhanced multifunctional coatingsfor cotton fabrics, Thin Solid Films 520 (2012) 4658.



[20] K. Li, X. Zeng, H. Li, X. Lai, H. Xie, Facile fabrication of superhydrophobic filtrationfabric with honeycomb structures for the separation of water and oil, Mater.Lett. 120 (2014) 255.

[21] R.V. Lakshmi, T. Bharathidasan, P. Bera, B.J. Basu, Fabrication of superhydropho-bic and oleophobic sol–gel nanocomposite coating, Surf. Coat. Technol. 206(2012) 3888.

[22] X. Zhou, Z. Zhang, X. Xu, X. Men, X. Zhu, Fabrication of super-repellent cottontextiles with rapid reversible wettability switching of diverse liquids, Appl. Surf.Sci. 276 (2013) 571.

[23] Z. Shi, I. Wyman, G. Liu, H. Hu, H. Zou, J. Hu, Preparation of water-repellentcotton fabrics from fluorinated diblock copolymers and evaluation of theirdurability, Polymer 54 (2013) 6406.

[24] N. Stolow, Action of solvents on dried linseed oil films, Nature 16 (1957)179.

[25] E. Carretti, L. Dei, R.G. Weiss, P. Baglioni, A new class of gels for the conservationof painted surfaces, J. Cult. Herit. 9 (2008) 386.

[26] S.D. Wang, S.S. Luo, Fabrication of transparent superhydrophobic silica-basedfilm on a glass substrate, Appl. Surf. Sci. 258 (2012) 5443.

[27] S.D. Wang, Y.Y. Shu, Superhydrophobic antireflective coating with high trans-mittance, J. Coat. Technol. Res. 10 (2013) 527.

[28] A. Groza, A. Surmeian, M. Ganciu, I.I. Popescu, Infrared spectral investigation oforganosilicon compounds under corona charge injection in air at atmosphericpressure, J. Optoelectron. Adv. M. 7 (2005) 2545.

Application of superhydrophobic sol gel on canvas

Documents

Transcript of Application of superhydrophobic sol gel on canvas