Accepted Manuscript

Chemical and Morphological Characterization of sulfonated Polystyrene Brush‐

es in Different Environments

Iñaki Zalakain, Nikolaos Politakos, Jose Angel Ramos, Ainara Saralegi, Haritz

Etxeberria, Iñaki Mondragon, M. Angeles Corcuera, Arantxa Eceiza

PII: S0014-3057(13)00194-8

DOI: http://dx.doi.org/10.1016/j.eurpolymj.2013.04.025

Reference: EPJ 6071

To appear in: European Polymer Journal

Received Date: 15 January 2013

Revised Date: 19 April 2013

Accepted Date: 29 April 2013

Please cite this article as: Zalakain, I., Politakos, N., Ramos, J.A., Saralegi, A., Etxeberria, H., Mondragon, I.,

Angeles Corcuera, M., Eceiza, A., Chemical and Morphological Characterization of sulfonated Polystyrene Brushes

in Different Environments, European Polymer Journal (2013), doi: http://dx.doi.org/10.1016/j.eurpolymj.

2013.04.025

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1

CHEMICAL AND MORPHOLOGICAL CHARACTERIZATION OF

SULFONATED POLYSTYRENE BRUSHES IN DIFFERENT

ENVIRONMENTS

Iñaki Zalakain, Nikolaos Politakos, Jose Angel Ramos, Ainara Saralegi, Haritz

Etxeberria, Iñaki Mondragon, M. Angeles Corcuera, Arantxa Eceiza*

‘Materials + Technologies’ Group. Dept. of Chemical and Environmental Engineering,

Polytechnic School, University of the Basque Country. Pza Europa 1, 20018 Donostia-

San Sebastián, Spain

* To whom all correspondence should be addressed. Tel.: (+34)943017185; fax:

(+34)943017130; e-mail address: arantxa.eceiza@ehu.es

ABSTRACT

Surface tethered polyelectrolyte polymer brushes composed of polystyrene (PS)

were grafted into a silicon wafer substrate. PS chains were polymerized by grafting

from method employing different reaction times in order to obtain polymer brushes with

different molecular weights. Then, the grafted polystyrene brushes were chemically

modified with a soft sulfonation reaction by employing different times of sulfonation.

The sulfonation degrees and chemical structure were analyzed by proton nuclear

magnetic resonance (1H-NMR) and Fourier transformed infrared spectroscopy (FTIR).

The grafted brushes were fully characterized by contact angle measurements and atomic

2

force microscopy (AFM) after exposed to solutions with different pH values. The

morphological analysis revealed different behaviour for the brushes depending on the

pH of the environments. By immersing polyelectrolytes brushes in water or in basic

solutions, polymer brushes that are negatively charged due to sulfonic acid group

deprotonation are formed, causing repulsion between the negative charges. This

repulsion stretched away the chains to the surface adopting an extended configuration.

Thus, brushes generated a continuous layer in the outermost surface of the brushes.

Therefore, in water or basic media, the configuration adopted by the brushes can be

considered as a uniform charged layer on top of the substrate. However, when the

samples were treated by an acid solution, brushes adopted a random distribution.

Contact angle (CA) measurements showed differences in surface arrangements keeping

in all cases the hydrophilic character of the surface.

KEYWORDS

Polymer brushes, polyelectrolyte, polystyrene, sulfonation, atomic force microscopy

(AFM).

3

INTRODUCTION

A polymeric brush is an array of macromolecular chains attached to a surface.

Polymer brushes attracted much interest in the 1950s when flocculation of dispersion

could be prevented by grafting molecules into the colloidal particles. Since then, a lot of

references can be found in the literature about synthesis, characterization and

applications of various kinds of polymeric brushes. Films consisted of polymer chains

that extend along a normal direction to the grafting surface exhibit different properties

from those in solution1. This ability of polymer brushes makes them an interesting field

for research. A lot of interesting properties are referred in the literature such as

interfacial localization of terminal groups2, diffusion control3, regulation of steric

repulsive forces4-5, control of phase-segregation in response to external stimuli6, wetting

control7, control of protein and cell adsorption8, adsorption of molecules9, lubrication10,

and adhesion11.

Polyelectrolyte brushes consider being a new class of material which recently

has received considerable interest. The strong segment-segment repulsions and the

electrostatic interactions present in such systems can lead completely new physical

properties of such monolayers in comparison with those consisting of either non-

stretched or non-charged polymer chains. Polyelectrolytes show an interesting property

due to the changes of their conformation in solution, depending on the environment

(acidic or basic). Usually, an acidic polymer will donate a proton (H+) to generate a

hydronium ion (H3O+) in water or in basic environment. On the contrary, in an acidic

environment, protons are plentiful and the polymer prefers to keep its proton and adopt

a hydrophobic behaviour (where a hydrophobic polymer in water will contract to avoid

water). In basic environments, the polyacid can donate its proton and due to the

4

coulombic repulsion between charged polymer segments, they will adopt swelled

conformation. This behaviour, under different environments, makes polyelectrolyte

brushes responsive materials. This can be useful for example with nanoparticles.

Collapsed brushes could cause encapsulation of the particles among polymer chains in a

specific environment and then by changing the environment, polymer chains will adopt

extended conformation and nanoparticles could be released12-13.

The most common methods for the synthesis of polymeric brushes are via

“grafting to”14-16 and “grafting from”6,17-18. Properties obtained by “grafting to” method

can be better controlled because the anchored polymer, which is synthesized previously,

is more homogeneous. Functionalized polymer is reacting with an appropriate group

from the substrate. However, due to increased viscosity during reaction, the obtaining

grafting density is lower by using this method19-20. In the case of “grafting from”, the

substrate is modified by anchoring an initiator, (usually with an organosilane) and vinyl

monomers are polymerized through solution17,21. In this case the achieved grafting

density is higher than with “grafting to” method, but control of molecular weight is

more complex.

Two different approaches are established for the creation of a polyelectrolyte monolayer

covalently attached to a solid surface. The first approach is anchoring directly polymeric

chains with polyelectrolyte groups in the structure, being this the most common strategy

employed to obtain polyelectrolyte brushes14,22-23. The most used polymers are

poly(acrylic acid) (PAA) and poly(2-vinylpyridine) (P2VP) which have side groups

with the capability to lose or gain protons. The other approach is to obtain

polyelectrolyte brushes by generate in situ polymer chains from a radical that is

immobilized on the solid surface or grafted previously onto the substrate. In this method

firstly the polymer brush is grafted onto the substrate, and then a chemical modification

5

is conducted on the polymer to obtain a polyelectrolyte brushes. The main advantage of

this method is the control of the modification reaction25-26. Other important issue in

polyelectrolyte brushes is related with the distinction between strong and weak

polyelectrolytes. In the case of strong polyelectrolytes, the number of charged groups

along the chains is fixed. However, the number of charged groups is variable in weak

polyelectrolyte brushes. Depending on this parameter, the brushes behaviour will be

different. In this work, due to the chemical modification is done in situ, the repulsion

between charged groups depend of modification degree. Thus, employing this method

the repulsion degree between charged groups can be controlled.

The aim of this manuscript is the synthesis of polystyrene brushes by “grafting

from” method on a planar silicon surface. Styrene was polymerized from the surface

after immobilization of the initiator. Polymerization was carried out by employing

different reaction times to obtain polystyrene polymer chains with different molecular

weights. Then PS brushes were modified by a soft sulfonation reaction giving

poly(styrene sulfonic acids). The influence of different environments in the sulfonated

polystyrene brushes behaviour were studied employing solutions with different pH

values (pH = 3, pH = 7 and pH = 13). Switching behaviour was studied by means of

atomic force microscopy analyzing the morphology adopted by brushes. Surface

hydrophilicity variations were studied by employing static water contact angle

goniometry.

EXPERIMENTAL SECTION

6

Materials: the styrene (St) monomer employed in the present study was distilled under

reduced pressure over calcium hydride (CaH2). Toluene, tetrahydrofuran (THF), 1,4-

dioxane and dimethyl sulfoxide (DMSO) were used as solvents and methanol as

precipitating agent for the obtained polymers. The employed organosilane was 3-

glycidoxypropyl trimethoxisilane (GPS) and the selected initiator was 4,4’-azobis(4-

cyanopentanoic acid) (ABCPA). All reagents were purchased from Aldrich (Germany).

Cyclohexane, sulfuric acid and acetic anhydride were employed in the preparation of

acetyl sulfate. Isopropanol was used as termination agent of the sulfonation reaction. All

the reagents employed in the sulfonation were used as received and they were purchased

from Panreac. Silicon wafers (100) employed as physical surfaces for polymer grafting

were purchased from Si-Mat (Germany).

Polymerization: in order to remove the outermost oxide layer from the silicon wafer

substrates and to generate hydroxyl groups in the surface, the wafers were first cleaned

in an ultrasonic bath for 15 min at 30 °C with dichloromethane, then were placed in a

mixture of water, ammonia solution (25% (aq.) v/v) and hydrogen peroxide (30% (aq.)

v/v) with a volume ratio 6:1:1 for 25 min at 80 °C and after this, rinsed several times

with Millipore water6. For the immobilization of the organosilane on the surface, the

silicon wafer was introduced in a solution containing 3-glycidoxypropyl

trimethoxisylane (GPS) in toluene (5% v/v) for 8 hours at 80 ºC. Then the silicon wafer

was washed by methanol and it was dried under a nitrogen flow. Subsequently silicon

substrate was introduced in a solution of 2% ABCPA in toluene (w/w) with pyridine as

catalyst. The mixture was maintained for 5 hours at 50 ºC under nitrogen atmosphere,

where the silicon wafer with the attached initiator was rinsed several times with THF

and then dried under a nitrogen flow. Styrene radical polymerization took place in

7

dioxane solution (1:1 v/v) at 60 ºC under inert atmosphere (N2) during 24 and 48 hours.

During this process two different polymers were obtained: one substrate grafted

polymer and other ungrafted polymer. Brushes polymerized at different times are

referred as PS24h and PS48h. Ungrafted polymer was precipitated in methanol and

silicon wafer surface was rinsed several times with THF.

Sulfonation: polystyrene brushes were sulfonated with acetyl sulfate in Figure 1 the

sulfonation reaction scheme was presented. The silicon wafer with PS brushes was

immersed in 72 mL of cyclohexane solution at 40 ºC. The acetyl sulfate solution was

prepared mixing 12 mL of dichloromethane and 2.4 mL of acetic anhydride under N2

atmosphere. This solution was cooled to 0 ºC and 0.9 mL of concentrated sulfuric acid

was added. The solution was kept until homogeneous colour was obtained. Once

prepared acetyl sulfate, brushes sulfonation reaction was carried out using different

times for the sulfonation (2h, 4h and 8h). The reaction was finished adding isopropanol

for 30 min and cooling until room temperature to avoid the formation of sulfone cross-

linking22,27-28. Three different sulfonation reactions were made to the PS24h and PS48h

polymers. The reactions were carried out during 2, 4 and 8 hours.

8

Figure 1: reaction scheme of sulfonation reaction: (a) preparation of acetyl sulfate and (b) sulfonation

reaction of PS.

Ungrafted polymer was used in order to evaluate the sulfonation reaction of

polystyrene. The same sulfonation times were employed to study differences in

sulfonation degree as well as for the grafted PS polymeric brushes.

Techniques

Size Exclusion Chromatography (SEC). Molecular weights of ungrafted different

polystyrenes were determined by size exclusion chromatography (SEC) using a Perkin-

Elmer chromatograph equipped with a binary pump and a refractive-index (RI) detector.

The eluent used was THF and the separation was carried out with four columns packed

with particle gels with different nominal pore sizes. Elution rate was of 1mL min-1 at 30

ºC. The molecular weights were based on a calibration curve from monodisperse

polystyrene standards.

Fourier-Transform Infrared Spectroscopy (FT-IR). Infrared analysis was performed on

a Nicolet Nexus 670 Fourier transform infrared (FTIR) spectrometer equipped with a

single horizontal golden gate attenuated total reflectance (ATR) cell. The spectra were

taken with a 2 cm-1 resolution in the range from 4000 to 600 cm-1 and an accumulation

of 20 scans.

Nuclear Magnetic Resonance Spectroscopy (NMR). 1H-NMR spectroscopy was used for

the verification of the synthesis and the determination of polystyrene and sulfonated

polystyrene chemical structures. PS samples were dissolved in deuterated chloroform

(CDCl3) and sulfonated PS samples in deuterated dimethyl sulfoxide (DMSO-d6). The

spectra were recorded at room temperature on an Avance Bruker 500 MHz

(Rheinstetten, Germany) equipped with BBO z-gradient probe Bruker DSX NMR

9

spectrometer using a rate of 5000 Hz and a frequency of 500 MHz and a delay between

pulses of 1s.

Atomic Force Microscopy (AFM). The surface morphology of the samples was

characterized by AFM with a Nanoscope IVa Dimension 3100 AFM (from Digital

Instruments). Tapping mode in air was employed using an integrated silicon

tip/cantilever (125 µm in length and with ca. 300 kHz resonant frequency) at a scan rate

of 1.0 Hz and a resonance frequency of ~300 kHz. The measurements were performed

with 512 scan lines. Several regions were scanned obtaining similar results.

Contact Angle Goniometry. Static contact angles of water (Millipore) was used to verify

any change in the sulfonated brushes structure by using Data Physics OCA 20 contact

angle systems. A short period of time (≈1 min) was chosen to avoid the reconformation

of brushes in contact with water.

RESULTS AND DISCUSSION

PS brushes polymerization

Polystyrene brushes were polymerized from the silicon wafer substrate

following the procedure described previously. The radical polymerization was carried

out using two different times. As it was previously mentioned, the ungrafted polymer,

which was isolated by precipitation, was employed to measure the molecular weight.

The measured molecular weights of polystyrene by SEC technique were M n = 265.000

gmol-1 with 2.1 polydispersity and M n = 390.000 gmol-1 with 2.2 polydispersity, for

PS24h and PS48h, respectively.

10

The morphological behaviour of PS24h and PS48h brushes were analyzed by

atomic force microscopy. Representative AFM images for PS brushes polymerized at

different times are shown in Figure 2. Here it should be noticed that both PS brushes

show similar morphologies and displaying dimple-like morphology in both cases

independently of polymer molecular weight.

Figure 2: AFM height images for a) PS24h and b) PS48h. Images size 1 x 1 µm. Z-axis scale 35 nm.

PS brushes sulfonation

The sulfonation reaction was carried out following the same procedure as

described elsewhere27-28. The chemical modification allowed controlling sulfonation

degree by employing different reaction times. The success of sulfonation reaction was

verified by 1H-NMR and FTIR spectroscopy and water contact angle measurements.

Figure 3 shows FTIR spectra of polystyrene and sulfonated polystyrene. The broad peak

over the region 3700-3000 cm-1 has been ascribed to stretching of hydroxyl groups of –

SO2-OH groups and water molecules retained by the sample. The bands of 1600 and

1500 cm-1 can be assigned to the stretching vibration of ring in plane. Comparing both

spectra, sulfonated polystyrene spectrum shows several bands which are not presented

in polystyrene spectrum at 1156, 1127, 1034, 1006 cm-1 (indicated by the arrows in Fig.

3). They are all representative of the stretching vibrations associated with sulfonic

11

group29. The in-plane bending vibrations of the aromatic ring (in styrene)

parasubstituted with the sulfonate group and the sulfonate anion attached to the

aromatic ring are represented at 1006 and 1127 cm-1, respectively, while the bands at

1034 and 1156 cm-1 represent the symmetric and asymmetric stretching vibrations of

the sulfonate group, respectively. The absence of this band in the PS spectrum

confirmed the successes in polystyrene correct sulfonation.

Figure 3: FTIR spectra of polystyrene and sulfonated polystyrene.

1H-NMR spectroscopy was used to analyze the sulfonation degree. Aromatic

protons of polystyrene give a chemical displacement between 6.0 and 7.3 ppm. The

signals of aromatic protons in sulfonated polystyrene shift from 6.0 to 8.0 ppm. By

employing different sulfonation reaction time, the characteristic chemical shifts of the

aromatic protons (for PS and sulfonated PS) were not change significantly. The degree

12

of sulfonation can be estimated from the ratio of the integrated area of the peaks

resulting from the aromatic (sulfonated and non-sulfonated) protons from the 1H-NMR

spectra. The obtained results for the sulfonation degree, employing different sulfonation

times for both samples are, shown in Table 1:

Polymer Sulfonation time

(hours) Sulfonation degree (%)

2 41

4 48 PS24h

8 45

2 46

4 43 PS48h

8 45

Table 1: results of sulfonation of polystyrene for 24 and 48 hours.

As can be seen in Table 1, the sulfonation degree for both polystyrenes and

different modification times are quite similar, 44.5 ± 3.5 and 44.5 ± 1.5 for PS24h and

PS48h, respectively. These results suggest that sulfonation time for each polystyrene

sample does not affect the sulfonation degree. In literature is suggested that after a

specific time for the sulfonation reaction (which could be established around 2h in this

case) further time for sulfonation does not affect significantly the degree of sulfonation

and a maximum is observed25,30.

Contact angle measurements were employed to analyse surface behaviour of

polystyrene and sulfonated polystyrene brushes. Figure 4 shows images of water drops

over the PS and sulfonated PS brushes. The contact angle values were 91° ± 2 and 25° ±

2 before and after the sulfonation (without any treatment), respectively. It is clear that

13

this modification become the surface more hydrophilic due to the interaction between

sulfonic acid group and water.

Figure 4: images from contact angle measurements for a) PS24h brushes and b) sulfonated PS24h

brushes.

Polyelectrolyte morphological behaviour in different pH media

The changes in morphology of sulfonated polystyrene brushes after 2 hours of

sulfonation were analyzed by AFM employing different solutions with three pH values:

3, 7 and 13 for 1 hour. AFM height images of the sulfonated PS24h brushes in different

environments are shown in Figure 5. On the bottom of the AFM images, surface section

profiles are shown, in order to depict better the morphology of the brushes. AFM results

reveal change in the morphology of sulfonated PS comparing with PS brushes (Figure

2) because of the change in chemical structure of the polymer chains. Figure 5a shows

the surface morphology of sulfonated PS24h after treatment in a solution with pH 3 for

1 hour. Several domains with ~ 40 nm in height appeared on the surface. Contact angle

measurements can be indicative of changes on the surface. After sulfonation reaction,

immersing the sample in a solution with pH 3, the brushes contact angle was 32° ± 2.

This value suggests that the brushes surface polarity changed from hydrophobic (for

PS24h) to hydrophilic (sulfonated PS24h) when sulfonated brushes were immersed in

an acidic environment. Sulfonated polystyrene brushes exhibited different behaviour

when they were treated with neutral (pH 7) and basic (pH 13) solutions for 1 hour.

14

Employing these environments, brushes exhibited totally smooth surfaces (Figure 5b

and 5c) without any characteristic features as can be observed in their section profiles.

Comparing with the contact angle measurements, small variations were observed for

brushes treated with pH 7 and pH 13 regarding to treatment with pH 3. The contact

angles were 22° ± 2 (pH 7) and 25° ± 2 (pH 13). These values suggested variations in

the brushes surface respect to brushes treated with pH 3. Surface displayed more

interaction with the water due to negative charges and solvation of ions.

Figure 5: AFM height images of sulfonated PS24h brushed after treatment employing solution with: a)

pH 3, b) pH 7 and c) pH 13. Image size 1 x 1 µm and Z-axis scale 25 nm.

The same procedure was carried out for the sulfonated PS48h sample. The

sample was immersed in solution with pH 3, 7 and 13, by using the same conditions as

the previous samples. AFM height images of the sulfonated brushes under solutions

with different pH values are shown in Figure 6. These brushes exhibited similar

behaviour comparing with the aforementioned PS24h sulfonated sample. Similar

morphologies (as the previous sample) appeared when the brush layer was exposed to

solutions with different pH values. An orientation was observed for sulfonated brushes

when immersed in a solution with pH 3. However, surface morphology changed

considerably when the brushes were treated using solutions with pH 7 and pH 13. In

15

both cases, AFM images reveal segregation on the surface of brushes under these

environments. Section profiles displayed smooth surfaces for both cases as before. Also

these brushes showed similar tendency in respect to the contact angles values.

Regarding to contact angle measurements, after treatment with a solution with pH 3,

surface showed hydrophilic behaviour (36° ± 2). Contact angle values decrease after

treatment with solution with pH 7 and pH 13 where values of 26° ± 2 and 45° ± 2,

respectively, were obtained.

Figure 6: AFM height images of sulfonated PS48h brushed after treatment employing solution with: a)

pH 3, b) pH 7 and c) pH 13. Image size 1 x 1 µm and Z-axes scale 40 nm.

In a previous work6, it was reported that the morphology of PS-PMMA brushes

grafted to the silicon substrate is switched under different environment. Solvents with

different affinity for both of the components were employed to analyzed brushes

behaviour. When brushes are exposed to an environment with a good solvent for PS, PS

domains adopt an extended conformation locating in the outermost layer and the

PMMA domains adopting a collapsed conformation were located in the bottom. Similar

behaviour was observed employing a solvent selective for PMMA and non-selective for

PS. Polyelectrolyte brushes exhibit similar behaviour under solution with different pH

values. In the case of sulfonated polystyrene brushes, when environment is neutral or

16

basic, sulfonate groups can lose a proton. This can cause repulsion between adjacent

charges along the polymer chains and orientate the polymer chains stretched away the

surface adopting extended morphology. However, if the brushes are immersed in acid

media, sulfur groups are not really affected because an excess of protons exist in the

surrounding environment, so random configuration is adopted from the brushes.

Both samples show similar behaviour in water or basic media, or in acid media.

The reason in changes in morphologies is illustrated in Figure 7. Immersion of

sulfonated brushes in water or basic media, sulfur group can lose the proton. This loss

caused repulsion between adjacent chains. This repulsion stretched away the chains to

the surface adopting an extended configuration. Thus, brushes can generate a

continuous layer in the outermost surface of the brushes. On the contrary, when the

polyelectrolyte brushes are immersed in an acidic environment, protons are plentiful and

the polymer keeps its proton. For this reason brushes showed a neutral behaviour among

chains without any repulsion or attraction. Thus, brushes can adopt a random dispersion

along the surface, similar to the non-sulfonated PS.

Figure 7: illustration of polyelectrolyte brushes behaviour under different media: a) water or basic and b)

acid.

17

Finally it has to be notes that the domains show differences in height between

the two samples, since the two samples have different molecular weight these

differences are related with molecular weight.

Respect to the contact angles, due to the possible lack of protons in the sulfonate

ion after treatment with solutions of pH 7 and pH 13, brushes will solvate having more

affinity with water during measurements comparing with brushes after acid treatment.

Thus, brushes showed more hydrophilic behaviour after water and basic solutions

treatments. It is also very important to mention the manner that roughness affects

contact angle through AFM measurements. As can be observed, in both cases

sulfonated brushes showed more pronounced roughness with pH 3 solution than in the

cases of neutral or basic environments. Between the last two environments, as observed

in the AFM profiles, samples treated with pH 13 show higher roughness surface than

treated with pH 7, which could explain differences in contact angle values in both

sulfonated polystyrenes (PS24h and PS48h) increasing hydrophobicity of the surfaces.

CONCLUSIONS

In summary, the polystyrene brushes were grafted at different times (24h and

48h) exhibiting different molecular weights. In order to obtain polyelectrolyte brushes,

chemical sulfonation modification was employed with different sulfonation reaction

times. By the use of 1H-NMR and FTIR spectroscopy the synthesis was evaluated and

found to be successful. Employing different modification times similar sulfonation

degrees were obtained in all cases. The surface morphology was analyzed by atomic

force microscopy and a comparison was done with contact angle measurements.

Polyelectrolyte brushes responses were studied by using solutions with different pH

18

values (acidic, neutral and basic). Under neutral and basic environment, deprotonation

of sulfonic acid group of the polystyrene due to repulsion between chains caused the

chains to stretch away from the surface to the topmost of the sample, obtaining a

smooth surface. AFM analysis showed a homogeneous layer for both samples in both

environments and the hydrophilic behaviour of the brushes was repeated. In addition, in

acidic environment the absence of attractive or repulsive interactions (because of the

abundance of H3O+ in the solution) made the sulfonated polymer brushes adopt a

random configuration of the chains, similar to non-sulfonated PS as it was observed

from the morphological analysis. The different molecular weight of the samples only

made the surfaces rough in the acidic environment as it can be seen from the images of

the AFM.

ACKNOWLEDGEMENT

Financial support from the Basque Government in the frame of Grupos

Consolidados (IT776-13) is gratefully acknowledged. Authors also acknowledge

funding from Spanish Ministry (MAT2009-12832 and MAT2012-31675) and Basque

Government through ETORTEK 11 nanoIKER (IE11-304) program. Moreover,

technical support provided by SGIker (UPV/EHU, MINECO, GV/EJ, ESF) is gratefully

acknowledged.

DEDICATION

This article is dedicated to Professor Dr Iñaki B. Mondragon, who passed away

just after his contribution to this work and who founded the research group “Materiales

+ Tecnologías” (GMT) in 1988.

19

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21

FIGURE CAPTIONS

Figure 1: reaction scheme of sulfonation reaction: (a) preparation of acetyl sulfate and

(b) sulfonation reaction of PS.

Figure 2: AFM height images for a) PS24h and b) PS48h. Images size 1 x 1 μm. Z-axis

scale 35 nm.

Figure 3: FTIR spectra of polystyrene and sulfonated polystyrene.

Figure 4: images from contact angle measurements for a) PS24h brushes and b)

sulfonated PS24h brushes.

Figure 5: AFM height images of sulfonated PS24h brushed after treatment employing

solution with: a) pH 3, b) pH 7 and c) pH 13. Image size 1 x 1 μm and Z-axis scale 25

nm.

Figure 6: AFM height images of sulfonated PS48h brushed after treatment employing

solution with: a) pH 3, b) pH 7 and c) pH 13. Image size 1 x 1 μm and Z-axes scale 40

nm.

Figure 7: illustration of polyelectrolyte brushes behaviour under different media: a)

water or basic and b) acid.

22

TABLE CAPTION

Table 1: results of sulfonation of polystyrene for 24 and 48 hours.

23

TABLE OF CONTENTS GRAPHIC

Title: Chemical and morphological characterization of sulfonated polystyrene brushes in

different environments.

Authors: Iñaki Zalakain, Nikolaos Politakos, Jose Angel Ramos, Ainara Saralegi, Haritz

Etxeberria, Iñaki Mondragon, M. Angeles Corcuera, Arantxa Eceiza

Graphic:

24

Highlights

• Polyelectrolyte PS brushes modified by sulfonation reaction were synthesized

• Effect of modification time in the sulfonation degree was analyzed

• The morphological behavior was examined employing solutions with different

pH-s

25

26

27

28

29

30

31

32

Polymer Sulfonation time (hours) Sulfonation degree (%)

2 41

4 48 PS24h

8 45

2 46

4 43 PS48h

8 45

33

TABLE OF CONTENTS GRAPHIC

Title: Chemical and morphological characterization of sulfonated polystyrene brushes in

different environments.

Authors: Iñaki Zalakain, Nikolaos Politakos, Jose Angel Ramos, Ainara Saralegi, Haritz

Etxeberria, Iñaki Mondragon, M. Angeles Corcuera, Arantxa Eceiza

Graphic: