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Thin Solid Films 483

A model of chain folding in Polycaprolactone-b-Polymethyl

Methacrylate diblock copolymers

Tamara Elzein*, Houssein Awada, Mohamad Nasser-Eddine, Christelle Delaite, Maurice Brogly

Institut de Chimie des Surfaces et Interfaces, 15 Rue Jean Starcky, 68057 Mulhouse, France

Received 22 November 2004; accepted in revised form 12 December 2004

Available online 20 January 2005

Abstract

This paper is an attempt to understand how Polycaprolactone-b-Polymethyl Methacrylate diblocks (PCL-b-PMMA) are organized in a

confined geometry such as nanometric thin films spin coated on gold coated substrates.

Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS), employed to characterize PCL-b-PMMA thin films,

allowed us to suggest an adsorption model of PCL-b-PMMA diblock copolymers in which PCL chains are almost perpendicular to the

substrate plane, while PMMA blocks seem to be flattened at the surface. These results were also supported by Atomic Force Microscopy

(AFM) that was extremely useful for the comprehension of PCL-b-PMMA diblocks behavior when adsorbed as thin films.

The combination of the experimental observations offered us the possibility to propose a model of chain folding in the PCL-b-PMMA

diblock copolymers after adsorption on chemically inert substrates.

D 2005 Elsevier B.V. All rights reserved.

Keywords: PCL-b-PMMA; Thin films; Organization; PM-IRRAS

1. Introduction

The interest of block copolymers is largely discussed in

the literature, and particularly, their ability to order into

nanometer sized domains making them suitable materials

for surface patterning for further use in divers applications

[1–6]. Many parameters could influence the characteristic

dimensions of the resulting morphology of block copoly-

mers [7–11]: the molecular weight, the volume fraction of

the components, the interaction between the blocks and

finally the molecular architecture of the block copolymer.

Polycaprolactone-b-Polymethyl Methacrylate (PCL-b-

PMMA) diblocks belong to the hydrophobic–hydrophobic

block copolymers family. The PCL is a semi-crystalline

polymer known for its biocompatibility, biodegradability

and for its utility in the biomedical domains [12–16].

0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.tsf.2004.12.026

* Corresponding author. Tel.: +33 3 89 60 87 78; fax: +33 3 89 60 87

99.

E-mail address: tamara_elzein@yahoo.fr (T. Elzein).

PMMA, an amorphous polymer (glassy at ambient temper-

ature) is widely used in different fields of applications. The

synthesis of PCL-b-PMMA with a perfect control of the

physico-chemical parameters [17] allowed us to work with a

well defined composition of these diblock copolymers.

In a previous work [18], we studied PCL chains

organization when adsorbed as thin films of nanometric

dimensions and we showed that PCL chains are adsorbed

almost perpendicularly on the gold substrate surface and we

were able to calculate the orientation angles and to correlate

them with the chain length and crystallinity.

In this present paper, we will analyze the effect of the

PMMA block on the PCL block organization and how it

influences the chain folding in thin films. For instance, we

will vary the fraction of PCL and PMMA components in the

diblock.

To reach our aim concerning the investigation of the

chain organization in the thin films, we employed two

surface characterization techniques: polarization-modulation

infrared reflection-absorption spectroscopy (PM-IRRAS)

and atomic force microscopy (AFM). By combining the

(2005) 388–395

Table 1

Composition of the PCL-b-PMMA diblocks

Diblock m n PCL Weight

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395 389

results extracted from these techniques, we discussed the

organization and chain folding of PCL-b-PMMA thin films

prepared on the gold surface.

(PCL monomers) (PMMA monomers) percentage vPCL

Diblock 1 48 75 41.4

Diblock 2 50 30 61.7

2. Materials and techniques

2.1. PCL-b-PMMA diblocks

The synthesis of these diblocks by an original method is

the subject of another paper in preparation. The general

formula of these diblocks is given in Scheme 1.

In this work, we will analyze two different diblocks:

a) Diblock 1: PCL-b-PMMA with a ratio of monomers

(m/n) equal to 48/75 (see Table 1).

b) Diblock 2: PCL-b-PMMA with a ratio of monomers

(m/n) equal to 50/30 (see Table 1).

Thin films of PCL-b-PMMAwere spin-coated from 2 g/l

solutions in toluene on gold coated glass slides. The latter

were prepared as follow: before gold deposition, glass slides

were cleaned with ethanol, treated by Argon plasma for 3

min at a power of 80 W, and heated at 50 8C for 30 min in a

piranha solution. After immersion of glass slides (12 h) in 3-

mercaptopropyltriethoxysilane solution (in toluene), 120 nm

gold (99.99% from Balzers) layer was coated under vacuum

(10�7 mbar). 3-Mercaptopropyltriethoxysilane (95%) from

ABCR was used as a coupling agent between glass slides

and gold coatings.

Thin films thickness was found to be ranging between 15

and 18 nm as estimated by ellipsometry measurements.

2.2. Differential Scanning Calorimetry (DSC)

Thermal analysis of pure PCL and PCL-b-PMMA

diblocks was performed with a Mettler TA 4000 differential

scanning calorimeter (the sample weight was ranging from

10 to 15 mg). Thermograms were recorded between �120

and 230 8C with a heating rate of 10 8C/min.

2.3. Atomic Force Microscopy (AFM)

AFM experiments are carried out using a Dimension 3000

AFM coupled to a Nanoscope IIIa electronic controller

(Digital Instruments, Veeco-FEI company, USA). All experi-

ments are performed in the dynamic mode (Tappingkmode-

Scheme 1. PCL-b-PMMA diblock copolymers.

Veeco). The AFM is equipped with the phase extender

electronic modulus, allowing to record the phase shift

variations DU between the instantaneous oscillation of the

tip and the oscillation applied to the cantilever in Tapping

mode. In our case, this phase shift strongly depends on the

local moduli between the different components of the

material and reflects the surface structure of the thin films

[19–25].

Silicon cantilevers (TESP-NCH) provided by Nano-

Sensors are used. The resonant frequency of the cantilever

is equal to 300 kHz and the spring constant k is equal to

40 N/m. All cantilever are equipped with an ultrasharp

conical silicon tip having a radius of curvature ranging

between 5 to 10 nm. Scan frequency (lines/s) never

exceeds 1 Hz for scan sizes of 10 Am�10 Am as well as

for 3 Am�3 Am. Analyses are recorded both in topo-

graphic mode (height) and phase imaging. The reproduci-

bility of the results was checked.

It is also important to mention that the measurements

were also performed at different amplitude level in order to

probe surface rigidity versus indentation on the basis of the

phase image. Nevertheless amplitude reduction never

exceeds 15%, corresponding to relatively low level of

force applied on the surface (blight tappingQ) [21–26]. In

this mode, topographic images are not supposed to be

perturbed by mechanical effects. Then differences on

phases images can be properly interpreted. It should be

noted that semicrystalline polymers are well suited for the

use of the phase mode since surface viscoelastic properties

between crystalline and amorphous regions are large.

2.4. Infrared spectroscopy

2.4.1. Transmission

Diblocks powder samples were analyzed by infrared

spectroscopy with the Transmission device. Measurements

were performed with an IFS48 Bruker spectrometer and

the number of scans was fixed to 100 with a resolution of

4 cm�1.

2.4.2. Polarization-Modulation Infrared Reflection-

Absorption Spectroscopy (PM-IRRAS)

Diblock thin films were analyzed by PM-IRRAS

spectroscopy. Measurements were done with an IF66S

Bruker spectrometer; spectra were recorded with a MCT

detector, under experimental conditions of 1000 scans,

resolution of 1 cm�1, 858 as beam angle of incidence and

with a 74 kHz modulation frequency. A ZnSe photoelastic

modulator provided by HINDSk is used.

Table 2

Characteristic infrared bands of PCL-b-PMMA

Position

(cm�1)

Vibrator Abbreviation

2999 Asymmetric CH3 stretching ras(CH3)

2949 Asymmetric CH2 stretching ras(CH2)

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395390

We used the second derivative method to determine the

number and the frequency of overlapped bands. Sharp bands

are fitted with a pure Lorentzian function, while large ones

are a combination of Lorentzian and Gaussian functions.

This latter is the consequence of the multiple Lorentzian

components summation.

2910 Symmetric CH3 stretching rs(CH3)

2865 Symmetric CH2 stretching rs(CH2)

1727 Carbonyl stretching r(C=O)1293 C–O and C–C stretching

in the crystalline phase

rcr

1240 Asymmetric COC stretching ras(COC)1190 OC–O stretching r(OC–O)1170 Symmetric COC stretching rs(COC)1150 C–O and C–C stretching in

the amorphous phase

ram

3. Results and discussion

3.1. PCL-b-PMMA bulk characterization

DSC measurements were necessary to analyze the

crystallinity of the PCL-b-PMMA diblocks. The obtained

thermograms allowed the determination of the melt

enthalpy, and considering the melt enthalpy of a totally

crystalline PCL (DH8f=142 J/g) [27,28], we calculated the

degree of crystallinity of the diblock Xcdiblock and the one

related to the PCL entity XcPCL (XcPCL=Xcdiblock/vPCL).XcPCL is found to be equal to 55% and 72% respectively for

Diblock 1 and Diblock 2, while it is equal to 77% in the case

of pure Polycaprolactone [18].

It is obvious that the presence of the PMMA block

(amorphous) leads to a decrease of the PCL block

crystallinity and this is more evident in Diblock 1 having

58.6% (w/w) of PMMA compared to Diblock 2 having only

38.3% of PMMA. However, this effect is expected due to

the steric hindrance of the PMMA block during the

crystallization of the PCL chains: the amorphous chains of

PMMA disturb the chain folding in the PCL block and thus

leading to a crystallinity reduce of this latter.

These diblocks, as well as pure PCL, were also analyzed

by infrared spectroscopy in the transmission mode. In Fig. 1,

Wavenumber [cm-1]

Abs

orba

nce

[arb

. uni

ts]

Diblock 1

Diblock 2

Pure PCL

Amorphous band

2997

.75

2951

.97

2866

.18

1725

.49

1487

.45

1436

.89

1396

.23

1368

.18

1297

.94

1274

.74

1242

.69

1193

.20

1146

.95

1044

.77

991.

0796

2.17

842.

7475

1.31

02

46

8

3000 2500 2000 1500 1000 500

Fig. 1. Comparison of pure PCL and diblocks bulk infrared spectra

(transmission device).

we compared pure PCL and diblocks (Diblock 1 and Diblock

2) spectra in the 800–3200 cm�1 region.

Observing Fig. 1, we can notice that the most relevant

differences between the pure PCL and the two diblocks arise

from two regions:

- The 1000–1200 cm�1 region where the C–C and C–O

stretching mode band of the amorphous phase is present

(around 1150 cm�1) [29].

- The 2500–3200 cm�1 region where the CH3 stretching

mode bands of the PMMA are present.

The totality of infrared vibrators and their wavenumbers

are gathered in Table 2 [29–33].

It is important to highlight the fact that the band at 1293

cm�1 related to the crystalline phase is exclusively a PCL

mode. Meanwhile, the band at 1150 cm�1 becomes very

strong in the diblocks spectra (and also increases from

Diblock 2 to Diblock 1), and thus confirming the increase of

the amorphous content as it was deduced from DSC

measurements. Concerning the other bands, they are

common to both blocks PCL and PMMA (except CH3

modes).

On the other hand, these spectra are considered to be

related to the isotropic response of these materials. This fact

is of major importance when discussing, later in the paper,

the chain orientation in the diblock thin films.

3.2. PCL-b-PMMA thin films

In this section, we will discuss PM-IRRAS and AFM

results separately.

3.2.1. PM-IRRAS spectroscopy

Before the discussion of results, we will remind the theory

of this technique that appears to be an excellent tool to access

chain orientation in thin films. The basic principle of the PM-

IRRAS method is to combine the FT-IRRAS experimental

conditions with a fast modulation of the polarization state of

the incident electric field (ideally between p and s linear

Wavenumber [cm-1]

Abs

orba

nce

[arb

. uni

ts]

Bulk Diblock 2

Diblock 2 thin film

02

46

8

3000 2500 2000 1500 1000

10

2952

.94

1739

.55

1369

.71

1296

.02

1244

.04

1193

.16

1151

.79

Fig. 2. Comparison of bulk and thin film spectra of Diblock 2.

Wavenumber [cm-1]

Abs

orba

nce

[arb

. uni

ts]

Pure PCL thin film

Diblock 2 thin film

02

46

8

3000 2500 2000 1500 1000

10

2952

.94

1739

.55

1369

.71

1296

.02

1244

.04

1193

.16

1151

.79

Fig. 3. Comparison of pure PCL and Diblock 2 thin films spectra (PM-

IRRAS device).

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395 391

states) and to extract, from the detected intensity (using

electronic filtering and demodulation), the two signals

(Rp�Rs) and (Rp+Rs) in order to finally compute the

differential reflectivity spectrum DR/R [34].

In details, this technique is based on three principles

[34–39]:

- Selection rules induced by the reflection on metallic

surface of infrared beam under grazing angles: remem-

bering first that an incident s-polarized light gives no

surface electric field and consequently no surface

absorption, we can see that PM-IRRAS should be a

very efficient way to discriminate near-surface absorp-

tion from the isotropic stray absorption occurring farther

into the sample environment. Second, that in case of

incident p-polarized, the surface electric field of the

resulting stationary wave is normal to the metal plane

and presents some intensity enhancement due to

constructive interferences.

- The double modulation of the incident beam: both a

Michelson interferometer and a Photoelastic modulator

(PEM) modulate infrared radiation from a conventional

IR source. The interferometer produces a signal at the

detector, which when demodulated is proportional to

the total light intensity reflected from the sample

surface (Rp+Rs). The PEM modulates between the

parallel (p) and perpendicular (s) components of the

light striking the surface such that after demodulation a

signal proportional to the difference in the intensities

of the two polarization components (Rp�Rs) is

obtained. These two signals can be demodulated

separately, because there is a large difference in the

modulation frequencies of the interferometer and the

PEM.

- The mathematical treatment of the detected signal in

order to obtain the differential reflectivity:

DR

R¼ Rp � Rs

Rp þ Rs

: ð1Þ

The big advantage of this technique is that the two

reflectivities Rp and Rs are simultaneously obtained (i.e.

during the same experiment) [40].

PM-IRRAS selection rules imply that the sign and the

intensity of an IR band is a function of the orientation of its

transition moment relative to the surface plane. Selection

rules are then: if the orientation of a transition moment is

parallel to the surface plane then the PM-IRRAS signal is

equal to zero. If the orientation is perpendicular to the

surface plane then the signal is maximal.

Experimentally, to access chains organization in thin

films, the comparison of the bulk and thin films spectra is the

primordial step since, according to selection rules, the

changes in bands intensities are related to the chain

preferential orientation. In that way, we compared (Fig. 2)

the spectrum of the Diblock 2 (bulk) with its PM-IRRAS one

(thin film).

Regarding Fig. 2, one can observe the important intensity

decrease of the band around 1150 cm�1 relatively to the

others in the thin film spectrum. As mentioned before, this

band is attributed to the amorphous phase and in majority it is

a PMMA contribution (see Fig. 1). Moreover, the bands

related to the CH3 stretching modes in the 2500–3000 cm�1

are no more clearly distinguished in the thin film spectrum.

As a consequence we can suppose, for instance, that PMMA

chains are flattened on the gold surface and are adopting a

conformation close to the isotropic one. But how to interpret

the entire diblock thin film spectrum? To answer this

Abs

orba

nce

[arb

. uni

ts]

νν(C O)νas(COC)

νs(COC)

Pure PCL

bulk

Thin film

Wavenumber [cm-1]

1727

.74

1472

.29

1421

.50

1369

.46

1297

.45

1242

.25

1189

.40

1164

.63

12

34

56

78

9

1800 1600 1400 1200

=

vcr

Fig. 5. Comparison of PCL spectra in the 1000–1800 cm�1 region.

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395392

question, we compared in Fig. 3, PM-IRRAS spectra of the

pure PCL and the Diblock 2 thin films.

As it can be easily observed in Fig. 3, the spectrum of the

diblock thin film is almost the same as the pure PCL thin

film. In a previous work [18], we analyzed in detail PCL

thin films and, on the basis of PM-IRRAS spectrum (the

same shown in Fig. 3) compared to the bulk transmission

spectrum (Figs. 4 and 5), we gathered many points useful to

reach the PCL chains orientation:

- rs(COC): As shown in Fig. 5, this band strongly

decreases in the PM-IRRAS spectrum indicating a

preferential orientation of this vibrator in the surface

plane. And since its transition moment is perpendicular

to the main chain axis, we deduce that this latter should

be in the normal direction with respect to the substrate

surface.

- ras(COC): oppositely to rs(COC), this vibrator keeps a

very strong band in the PM-IRRAS spectrum (Fig. 5).

Taking into account the fact that this vibrator is in the

main chain axis direction, we deduce that its important

signal in the thin film spectrum is the consequence of a

quasi-perpendicular orientation of the chain axis on the

substrate surface. Moreover, ras(COC) is in the chain

plane, and thus we can conclude that this latter is also

preferentially oriented in the normal direction.

- rs(CH2) and ras(CH2): the intensity decrease of these

two vibrators bands in the 2800–3000 cm�1 (Fig. 4) is

due to a parallel orientation of their transition moments

with respect to the surface. The unique possibility to

obtain such an orientation of these two vibrators is to

have the main chain axis and plane quasi-perpendicular

to the surface. This deduction is in excellent agreement

with all the other experimental observations mentioned

above.

Wavenumber [cm-1]

Abs

orba

nce

[arb

. uni

ts]

TIR (Bulk)

PM-IRRAS (thin film)

Pure PCL

02

46

8

3000 2500 2000 1500 1000

75

31

2948

.22

2867

.74

1729

.69

1471

.25

1369

.45

1297

.99

1243

.65

1179

.10

1102

.71

1045

.22

Fig. 4. Comparison of PCL bulk and thin film spectra in the 1000–3000

cm�1 region.

Basing on these different points, we elaborated an

adsorption model of pure PCL in which the main chain

axis CC and the CCC plane of the PCL are almost

perpendicular to the substrate surface (Scheme 2) and that

for different chain lengths. This preferential orientation

could be probably imposed during thin film crystallization

at the gold surface since that PCL seems to remain

crystalline even in the confined geometry (apparition of

the crystalline band in the thin film spectrum). Thus in the

case of the diblock thin film spectrum, being identical to that

of the pure PCL thin film, we can suggest the same

preferential orientation of the PCL crystalline chains in the

diblock thin film. Even if many bands are common between

PCL and PMMA, the chain flattening of the PMMA block

ϕ

α

H

H

H

H

H

H

H

H

H

H

O

O

O

u

v

w

x

z

y

Scheme 2. Adsorption model of PCL chains at the gold surface.

a)

Diblock 2

Diblock 1

b)

-9

-6

-3

0

3

6

9

0 1 2

Length (Microns)

Hei

ght (

nm)

Fig. 6. (a) AFM Topographic images of Diblock 1 and Diblock 2 thin films

(10�10 Am) taken with rsp=0.89. The number of fingerlike patterns

increases with the increasing length of the PCL block (from Diblock 1 to

Diblock 2). (b) line scan image of the Diblock 2 thin film.

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395 393

would induce a quite disappearance of the PMMA

contribution in the thin film spectrum (according to PM-

IRRAS selection rules), and this could be justified by the

amorphous nature of the PMMA (absence of important

forces such crystallization to promote a preferential ori-

entation). Thus, the resulting spectrum of the diblock thin

film is considered in majority, as a first approximation, as

the contribution from the PCL crystalline phase.

As a consequence, we can suggest an adsorption model

of the PCL-b-PMMA copolymers on the gold surface in

which the PCL crystalline chains are oriented almost in the

normal direction (with respect to the gold substrate surface)

while no preferential orientation is observed for the PMMA

block. However, a complete description of this model could

not be given without an AFM analysis of the diblocks thin

films.

3.2.2. AFM analyses

3.2.2.1. Effects of PCL and PMMA block lengths. Fig. 6a

represents a comparison of topographic images (10 Am�10

Am) for two samples of PCL-b-PMMA thin films (Diblock

1 and Diblock 2).

Both images show characteristic fingerlike patterns.

Number of fingerlike patterns increases when the length

of the PCL block relative to the PMMA one increases. One

could consider that the fingers correspond to the organ-

ization of PCL crystalline phase. On the other hand, the

difference in height between the apparently amorphous

phase (between fingerlike patterns) and crystalline one

(fingerlike patterns) is 10 nm as confirmed by the measure-

ment of the linear scan (Fig. 6b). Some important questions

should be asked at this point: Do the fingerlike patterns

really correspond to crystalline organization of PCL blocks?

If yes what is the phase structure profile i.e. does crystalline

nuclei form at the interface or not? Where is the amorphous

PMMA phase located?

3.2.2.2. Probing fingerlike patterns with AFM. In order to

identify the difference of surface rigidity of the PCL-b-

PMMA thin films we have performed Tappingk Mode

AFM measurements at different tapping forces on the

Diblock 2 sample. Three parameters must be considered

in estimating the tapping force: the free amplitude A0; the

setpoint ratio rsp; the cantilever spring constant k. The

free amplitude is the oscillation amplitude of the canti-

lever when there is no interaction with the surface of the

sample. The setpoint ratio rsp equals Asp/A0 where Asp,

the setpoint amplitude, is the amplitude of the cantilever

when it has been reduced by interaction with the sample.

In the case of polymer surface that is prone to surface

indentation, Asp is equivalent to the tip-surface distance

(dsp) plus the indentation depth of the tip into the sample

(zind). Changing rsp value has been found to lead to great

differences in the phase images obtained [41,42]; rspshould be close to unity for reducing the force applied to

the surface of the sample and as rsp is lowered the applied

force increases and it is possible to image subsurface

features [41–43]. Fig. 7 (a, b and c) shows a characteristic

PCL-b-PMMA (Diblock 2) fingerlike pattern imaged at

different rsp values, respectively 0.79, 0.74 and 0.69. The

PCL layer (10 nm)

PMMA layer (8 nm)

Gold substrate

Scheme 3. Adsorption model of PCL-b-PMMA on the gold surface.

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395394

resulting topographic and phase shift images are presented

in the left and right panels respectively (in Fig. 7).

As rsp decreases the amplitude of the tip oscillation

increases and topographic images are rather similar but on

phase shift images great differences are observed: the

difference in mechanical properties of the different regions

clearly emerges. On the color scale, dark zones correspond

to soft regions and bright zones to hard ones. On Fig. 7a, at

small tapping force, the region between fingers is rather

dark (i.e soft) and as tapping force increases (Fig. 7b and c)

brighter zones emerge delimiting regions with different

mechanical properties that correspond to the finger mor-

phology. This observation allows us to confirm that regions

between fingerlike patterns correspond to the amorphous

PMMA blocks and thus when the tapping force increases

this layer is indented and the tip becomes sensitive to the

gold substrate (bright) which rigidity is greater than the

PMMA one. On the other hand, as we said before, fingerlike

patterns correspond probably to the crystalline organization

of PCL blocks, but when observing Fig. 7 (a, b and c) we

noticed that they appear in dark at small tapping forces and

as rsp decreases they become brighter leading us to suspect

that a thin PMMA amorphous film could also be present on

the surface of the crystalline fingers of PCL and thus at high

rsp fingers appear also in dark and at low rsp the PMMA

layer is indented and tip becomes sensitive to the PCL

crystalline phase (brighter) which is stiffer than PMMA and

softer than the gold substrate. According to this scheme,

crystallization of PCL is initiated at the substrate interface.

We can also estimate to a first approximation the height of

the PMMA layer on the basis of the phase images at

a)Topography Phase

0 nm

15 nm

30 nm

0°

40°

80°

b)

0°

40°

80°

0 nm

15 nm

30 nm

c)

0°

40°

80°

0 nm

15 nm

30 nm

Fig. 7. AFM topographic and phase images of the Diblock 2 film obtained

at different set point ratio rsp, (a) rsp=0.79; (b) rsp=0.74; (c) rsp=0.69.

different setpoint ratio. A reduction of setpoint ratio from

0.79 to 0.69 corresponds to a reduction of probing

amplitude of 8 nm (free amplitude is initially set to 80

nm). This result means that the thickness of the PMMA

layer is 8 nm [equal to (0.79–0.69).80].

3.3. Adsorption model of PCL-b-PMMA thin films

By combining PM-IRRAS and AFM results we are now

able to propose a scheme to describe the blocks organization

in the PCL-b-PMMA thin films (Scheme 3). For that we

remind the main data extracted from PM-IRRAS and AFM

experiments:

- PCL crystalline chains are oriented almost in the normal

direction (with respect to the substrate).

- No preferential orientation is detected for PMMA chains

and an isotropic conformation seems to be favored.

- The phase between the fingerlike patterns of the PCL is

the amorphous PMMA.

- The surface of the crystalline fingers of PCL is covered

by a PMMA amorphous film; the PMMA layer is 8 nm

thick as estimated by AFM.

- The PCL layer is 10 nm thick obtained from line scan

images (AFM).

4. Conclusion

In this work, we were interested in PCL-b-PMMA

diblock copolymers and their organization when confined

in thin films on gold substrates. The access to the adsorption

model of these diblocks was based on two surface

techniques highly dedicated for thin films analyses: the

PM-IRRAS and AFM.

Our results allowed us to prove that the orientation of

PCL crystalline chains is not affected by the presence of the

PMMA block, and that by comparing with pure PCL thin

films, a preferential orientation close to the normal direction

T. Elzein et al. / Thin Solid Films 483 (2005) 388–395 395

was detected for PCL crystalline chains, while the PMMA

block seems to be completely isotropic. Moreover, AFM

analyses were complementary to PM-IRRAS and offered us

the possibility to elaborate a representative model of chains

adsorption on the gold substrate and to deduce that PCL

nucleation takes place on the gold interface leading to a

reject of PMMA block around the PCL one as shown in

Scheme 3.

References

[1] R.A. Segalman, A. Hexemer, R.C. Hayward, E. Kramer, Macro-

molecules 36 (2003) 3272.

[2] M. Park, C. Harrison, P.M. Chaikin, R.A. Register, D.H. Adamson,

Science 276 (1997) 1401.

[3] R.R. Li, P.D. Dapkus, M.E. Thomson, W.G. Jeong, C. Harrison, P.M.

Chaikin, R.A. Register, D.H. Adamson, Appl. Phys. Lett. 76 (2000)

1689.

[4] K.W. Guarini, C.T. Black, K.R. Milkove, R.L. Sandstrom, J. Vac. Sci.

Technol. 19 (2001) 2784.

[5] C.T. Black, K.W. Guarini, K.R. Milkove, S.M. Baker, T.P. Russell,

M.T. Tuominen, Appl. Phys. Lett. 79 (2001) 409.

[6] J.Y. Cheng, C.A. Ross, V.Z.H. Chan, E.L. Thomas, R.G.H.

Lammertink, G.J. Vansco, Adv. Mater. 13 (2001) 1174.

[7] U. Jeong, D.Y. Ryu, D.H. Kho, D.H. Lee, J.K. Kim, T.P. Russell,

Macromolecules 36 (2003) 3626.

[8] P. Mansky, C.K. Harrison, P.M. Chaikin, R.A. Register, N. Yao, Appl.

Phys. Lett. 68 (1996) 2586.

[9] A. Averopoulos, V.Z.H. Chan, V.Y. Lee, D. No, R.D. Miller, N.

Hadjichristidis, N.L. Thomas, Chem. Mater. 10 (1998) 2109.

[10] F.S. Bates, G.H. Fredrickson, Annu. Rev. Phys. Chem. 41 (1990) 525.

[11] I.W. Hamley, The Physics of Block Copolymers, Oxford University

Press, Oxford, 1998.

[12] H.Y. Kweon, M.K. Yoo, I.K. Park, T.H. Kim, H.C. Lee, H.-S. Lee,

J.-S. Oh, T. Akaike, C.-S. Cho, Biomaterials 24 (2003) 801.

[13] A.P.D. Elfick, Biomaterials 23 (2002) 4463.

[14] M. Rutkowska, React. Funct. Polym. 38 (1998) 27.

[15] J. Wang, M.K. Cheung, Y. Mi, Polymer 43 (2002) 1357.

[16] M.F. Koenig, S.J. Huang, Polymer 36 (1995) 1877.

[17] M. Nasser-Eddine, D. Sc Thesis, Mulhouse-France, 2003.

[18] T. Elzein, M. Nasser-Eddine, C. Delaite, S. Bistac, Ph. Dumas,

J. Colloid Interface Sci. 273 (2004) 381.

[19] G. Bar, R. Brandsch, M. Bruch, L. Delineau, M.H. Whangbo, Surf.

Sci. 444 (2000) L11.

[20] G. Bar, L. Delineau, R. Brandsch, M. Bruch, M.H. Whangbo, Appl.

Phys. Lett. 75 (1999) 4198.

[21] S.N. Magonov, V. Elings, M.H. Whangbo, Surf. Sci. 375 (1997) L385.

[22] D. Sarid, T.G. Ruskill, R.K. Workman, D. Chen, J. Vac. Sci. Technol.,

B 14 (1996) 864.

[23] D. Krqger, B. Anczykowski, H. Fuchs, Ann. Phys. 6 (1997) 341.

[24] S.N. Magonov, V. Elings, V.S. Papkov, Polymer 38 (1997) 297.

[25] G. Bar, Y. Thomann, R. Brandsch, H.J. Cantow, M.H. Whangbo,

Langmuir 13 (1997) 3807.

[26] J. Mallegol, O. Dupont, J.L. Keddie, Langmuir 17 (2001) 7022.

[27] D. Keroack, Y. Zhao, R.E. PrudThomme, Polymer 40 (1998) 243.

[28] B. Wunderlich, Macromolecular Physics, vol. 3, Academic Press, NY,

1973.

[29] M.M. Coleman, J. Zarian, J. Polym. Sci., B 17 (1979) 837.

[30] B. Schrader, Infrared and raman spectroscopy, methods and applica-

tions, VCH, 1995.

[31] D.O. Hummel, Infra Red Spectra of Polymers, Wiley & Sons, NY,

1966.

[32] L.J. Bellamy, Infra Red Spectra of Complex Molecules, 2nd ed.,

Wiley & Sons, NY, 1958.

[33] G. Socrates, Infra Red Characteristic Group Frequencies, Wiley &

Sons, NY, 1980.

[34] T. Buffeteau, B. Desbat, J.M. Turlet, Appl. Spectrosc. 45 (1991) 380.

[35] T. Elzein, M. Brogly, G. Castelein, J. Schultz, J. Polym. Sci., B 40

(2002) 1464.

[36] T. Elzein, M. Brogly, J. Schultz, Polymer 34 (2002) 4811.

[37] T. Elzein, M. Brogly, J. Schultz, J. Surf. Interf. Anal. 35 (2003) 231.

[38] T. Elzein, M. Brogly, J. Schultz, Polymer 44 (2003) 3649.

[39] T. Elzein, M. Brogly, J. Schultz, J. Surf. Interf. Anal. 35 (2003) 785.

[40] T. Buffeteau, B. Desbat, E. Pere, J.M. Turlet, Mikrochim. Acta 14

(1997) 627.

[41] A. Knoll, R. Magerle, G. Krausch, Macromolecules 34 (2001) 4159.

[42] A. Buzin, Y.K. Godovsky, N.N. Makarova, J. Fang, X. Wang, C.M.

Knobler, J. Phys. Chem., B 103 (1999) 11372.

[43] J. Feng, L.T. Weng, C.M. Chang, J. Xhie, L. Li, Polymer 42 (2001)

2259.