Preparation and surface properties of latexes with fluorine enriched in the shell by silicon monomer crosslinking

European Polymer Journal 43 (2007) 2117–2126

EUROPEAN POLYMER JOURNAL www.elsevier.com/locate/europolj

Preparation and surface properties of latexes with fluorine enriched in the shell by silicon monomer crosslinking Ping ting Xiong, De ping Lu *, Pei zhi Chen, Hong zhi Huang, Rong Guan Ministry of Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Department of Chemistry, Hubei University, Wuhan 430062, China Received 15 March 2006; received in revised form 20 December 2006; accepted 21 December 2006 Available online 10 January 2007

Abstract A series of core–shell acrylic copolymer latexes containing fluorine enriched in the shell have been prepared by emulsion polymerization of a variety of hydrocarbon monomers with (perfluoroalkyl)methyl methacrylate and vinyltriethoxysilicone. In the presence of a reactive anionic and a long chain anionic–nonionic emulsifier, the core–shell latexes were prepared and characterized by transmission electron microscopy (TEM) and tapping-mode atomic force microscopy (AFM). From AFM and contact angle measurements, it was observed that the resulting fluorine and silicon-containing acrylic copolymers with surface energy as low as 15.5 mN/m formed a dense and gradient film containing a surface layer with high a fluorine content, and that the fluorinated particles can be fixed on the surface due to the crosslinking reaction of multi-functional silicon monomer even though the fluorinated carbon number was not enough to crystallize.  2007 Elsevier Ltd. All rights reserved. Keywords: Fluorine; Silicon; Surface properties; Core–shell; Acrylic latex

1. Introduction Fluoropolymers exhibit a unique combination of high mechanical and thermal stability, chemical inertness (to solvents, chemicals, acids and bases), low friction coefficients, low flammability, excellent weatherability, good resistance to oxidation, extremely low surface energy and related unwettability, and relatively low permeability for most gases * Corresponding author. Tel.: +86 27 50865330; fax: +86 27 88663043. E-mail address: [email protected] (D.p. Lu).

[1,2]. The outstanding properties of fluoropolymers especially the low surface energy have stimulated their application in many high technology applications (aerospace, microelectronics, paints and coatings, etc.). Silicon-containing polymers represent attractive surface properties coupled with an exceptionally low glass transition temperature, low elastic modulus, and high thermal and chemical stability [3]. New polymer architectures combining in a single polymer the unique properties of both fluorinated and silicated polymers can provide interesting new materials, particularly with regard to potential for nonwetting surfaces with low surface energy.

0014-3057/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2006.12.040

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Although there are obvious advantages and benefits in fluorinated and silicated polymers, exceptionally reduced surface tension and solubility in aqueous environments of fluorinated monomers make synthetic efforts quite challenging. Several synthetic attempts [4–7] have been made to produce F-containing colloidal dispersions in organic solvents, including high shear rates, homogenizers, fluorinated surfactants, and these approaches have been somewhat successful. Among all factors of emulsion polymerization, the choice of emulsifiers is the most important. Linemann et al. prepared fluorine-containing polymer latex particles by emulsion polymerization [7]. Their synthesis using cetyltrimethylammonium bromide as emulsifier led to low monomer conversion accompanied by substantial losses of the fluorine-containing acrylate monomer due to severe coagulation during polymerization and storage. As we know, reactive emulsifiers can react with monomers and become a part of the copolymers, which decreases the negative effects of general emulsifiers on the nature of the latex films, and short chain emulsifiers are always expelled to the film surfaces during film formation, which would influence the film properties [8]. Another problem influencing the film properties is that the fluorinated groups may migrate to the inside of films when the environment surrounding the latex changes, for example, by being immersed into the water [9]. It has been reported [10] that the fluoroalkyl side chains of acrylate/methacrylate copolymers with a fluorinated carbon number of seven or more can be crystallized or liquid-crystallized. Wang et al. [11] found that for monodisperse polystyrene-fluorinated alkyl ester side chain block copolymers, the C6F13 form exhibited surface reconstruction after water exposure whereas the C8F17 form remained crystalline without noticeable surface reconstruction. However, if we can fix the fluorinated groups on the surface, there is no need for long chain perfluoroalkyl groups. Surface properties are usually governed by the structure and chemical composition of the outermost surface layer. The fluorinated species would migrate toward the air/film interface to minimize the interfacial energy [12–19]. The key to achieving good surface properties is that the surface of a material is covered with as many perfluoroalkyl groups as possible. A core–shell structure can provide some good properties for latex films, when polymers forming the core and the shell phase disperse totally or partially in the film. However, previous studies have shown that

[20] the synthesis of core–shell particle is not straightforward and its success depends on many parameters, such as the synthesis technique (batch, semicontinuous, and continuous polymerization) or the degree of incompatibility between the polymers which form the core and the shell of the particles. Thus, although the synthesis method of this kind of fluoropolymer is very important, it has scarcely been reported [21]. In this work, we report a convenient yet novel way of synthesizing fluorinated and silicated copolymers which utilized monomer-starved conditions to produce core–shell structure colloidal particles with shell layer enriched in fluorine by silicon monomer crosslinking. The synthesis of fluorine and siliconcontaining copolymers were prepared by using a mixed emulsifier system composed of a reactive emulsifier and a long chain anionic–nonionic conventional emulsifier which are compatible with the fluorine monomers. Although the fluorinated monomer had a fluorinated carbon number of six which was not enough to crystallize, the incorporation of silicated monomer which had multi-functional groups can be used as a crosslinker to fix fluoroalkyl groups on the surface of the latex. The incorporation of fluorinated and silicated monomers into copolymers were characterized by infrared spectra (IR) and 19F NMR. The latex particle morphology was characterized by TEM. The fluorine enrichment in the surface of the film was examined by contact angle measurements and the surface morphology was characterized by AFM. 2. Experimental 2.1. Materials Dodecafluoroheptyl methacrylate monomer (FMA)(99.5+%) and vinyltriethoxysilicone (VTES) (98+%) were used as received. Styrene (St)(99+%), methyl methacrylate (MMA)(99.5+%), butyl acrylate (BA) (99+%) and glycidyl methacrylate (GMA)(99+%) were all used as received, too. The crosslinking agent acetoacetic ethyl methacrylate (AAEM)(99.8+%) and initiator ammonium persulfate (APS) was used without further purification. The mixed emulsifier systems were composed of sodium 3-allyloxy-2-hydroxy-propane sulfonate (COPS-1)(40+%) and ammonium p-nonyl phenoxy polyoxyethylene(4) sulfate (C0-436)(58+%), which were both supplied from Rhodia France Inc. and used as received. Scheme 1 illustrates the structural formulae of FMA, VTES, COPS-1, and CO436.

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O H F3C C

O

CH3

C

C

tor solution was injected into the reaction kettle, which contained 28% (w/w) concentration of CO436, 42% (w/w) concentration of COPS-1 and 30 g of water. Three minutes later, a 50% (w/w) concentration of the pre-emulsion composed of all of St, BA, MMA, GMA, 72% (w/w) concentration of CO436, 58% (w/w) concentration of COPS-1, 18% (w/w) concentration of APS, and 25 g of water was added to the reactor over a period of 1 h. The remaining pre-emulsion with FMA and VTES were fed continuously over a period of 75 min, and the rest of initiator solution was fed over 80 min. Upon the completion of the initiator feeding, polymerization was allowed to continue for an additional 1.5 h at 82 C. A coagulate-free and long-time stable latex with a particle diameter of about 130 nm was obtained. The resulting acrylic copolymer emulsion had a weight percent solid content of about 43. Synthetically, the parameters varied including the amounts of FMA, and VTES. Table 1 lists the resulting particles sizes, solid content (w/w), conversion, and concentration levels of FMA and VTES.

CH2

CH2 F C

C CF3

CF3 F

F FMA

C 2H 5O H 2C C

OC2H5

Si

H

OC2 H5 VTES

H 2C

H H

H

C

O C

C

C

H

H

H

H

C

OH H SO3Na

2.3. Characterization

COPS-1

C9H19

2119

OCH2CH2 4SO3 NH4 CO436

Scheme 1. Structure of FMA, VTES, COPS-1, and CO436.

2.2. Preparation of acrylic copolymer The reaction was carried out in a four-neck round-bottomed flask equipped with a magnetic stirrer, thermometer, addition funnel, and reflux condenser. When the temperature of the water bath reached 82 C, a 45% (w/w) concentration of initia-

The solid content and the conversion were measured by gravimetric analysis. One to two gram of latex was cast onto a petri dish and dried at 115 C for 20 min. The solid content and the final conversion were calculated by the following equations, respectively: W2W0 Solid content ðwt:%Þ ¼  100%; ð1Þ W1W0 where W0 is the weight of the petri dish and W1 and W2 are the weights of latex before and after drying to the constant weight, respectively. Conversion ðwt:%Þ ¼

Solid content ðwt:%Þ  ðW 3  W 4 Þ  100%; W5 ð2Þ

Table 1 Preparation of F, Si-containing colloidal dispersions

FMA-0 FMA-5.89 FMA-8.24 VTES-0 VTES-0.33 VTES-0.66

FMA (% w/wa)

VETS (% w/wa)

Particle size (nm)

Polydispersity index

Solid content (% w/w)

Conversion (%)

0 5.89 8.24 4.12 4.12 4.12

0.33 0.33 0.33 0 0.33 0.66

128.2 130.4 131.7 130.9 137.1 147.3

0.0687 0.0367 0.0728 0.0045 0.0649 0.0284

43.27 43.53 44.26 43.96 44.58 44.83

95.74 96.31 97.94 97.25 98.63 99.19

% w/wa: indicates the percent of total charge weight.

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where W3 is the total weight of all the materials put in the flask before polymerization, W4 is the weight of the materials that could not volatilize during the drying period, and W5 is the total weight of the monomers. IR was recorded with a Perkin–Elmer FT-IR spectrophotometer. 19F (vs. CF3CO2H) NMR spectra were obtained on a Varian Unity Inova 600 NMR spectrometer using chloroform-d (CDCl3) as the solvent if not otherwise specified. Latex particles sizes were determined by means of light scattering using the Zetasizer 3 of Malvern using a He–Ne laser (632.8 nm, 5 mW), a photomultiplier, and an angle of 90. TEM photographs of the composites were obtained at 60 kV using a TEM-100SX. The latexes were negatively stained with an aqueous solution of 2% uranium acetate (UAc). In order to prepare the samples, the latex was diluted to about 0.1 wt.% solids and a drop of UAc was added to a 5 ml portion of the diluted solution. A drop of the resulting mixture was then placed on a formvar-coated grid and the water was removed by adsorbing it with a filter paper. Micrographs were recorded on negative films, which were subsequently scanned. The copolymer films for the analysis were prepared by casting copolymers onto teflon plates (6 · 6 cm2) and letting the solvent evaporate slowly at room temperature. The thickness was about 300 nm. Contact angle experiments were carried out on a ¨ SS processor tensiometer (K-12, Germany) KrU with the plate method under 25 C with deionized water and n-hexadecane, n-hexane was used to measure the wetting length. Immersion/withdrawal rates were 100 lm/s, and dwell times between immersion and withdrawal were 10 s, unless otherwise specified. Reported contact angles were averages of several determinations made on different areas of a sample surface. Accuracy was generally 1–2. AFM measurements were performed by imaging samples with a digital instruments nanoscope IIIa with a multimode head. The height and the phase images were obtained simultaneously while the instrument was operated in the tapping-mode under ambient conditions. Commercial Si cantilevers with force constants of 13–70 N/m were used. The data were taken at the fundamental resonance frequency of the cantilevers which was around 300 kHz. The root-mean-square roughness (Rq) was calculated by the software as

rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi P i ðZ i Þ2 ; Rq ¼ N

ð3Þ

where Zi is the height value and N the number of points measured on the surface analyzed. For AFM measurements, 1–2 drops of the corresponding dispersions (43 wt.% solid content) were cast onto freshly cleaved glass plates and then dried at room temperature. 3. Results and discussion 3.1. Preparation and characterization of core–shell latex Acrylic copolymers with fluorine enriched in the shell and high monomer conversion (>95%) have been prepared. The incorporation of the FMA and VTES in the copolymers was confirmed by IR (Fig. 1) and 19F NMR (Fig. 2). From the IR spectrum of the latex film (Fig. 2a), it can be seen that the characteristic absorption of the C@C bond in FMA monomer at 1640 cm1 has disappeared, indicating that the monomer FMA has copolymerized into the polymer chain. Comparing the copolymer IR spectrum with and without FMA, the IR absorption peak of acrylic latex with FMA fraction of 8.24% at 1100–1260 cm1 became wider and blunter, which is resulted from the stretching vibration absorption of the CAF bond at 1100– 1240 cm1, overlapping with the stretching vibration absorption of the CAOAC bond of ester groups at 1250 cm1. In Fig. 1b, the characteristic absorption of the C@C bond at 1640 cm1 has disappeared, indicating that the monomer VTES has copolymerized into polymer chain, too. Comparing the copolymer IR spectrum with and without VTES, the IR absorption peak of acrylic latex with VTES fraction of 0.66% at 937 cm1 and 1385 cm1 were assigned to the characteristic absorption band of SiAC bond, the peaks between 950 and 1050 cm1 were assigned to the characteristic absorption band of SiAOASi and SiAOAC bonds. All of this showed that FMA and VTES have copolymerized with acrylic monomers. The 19F NMR spectra of copolymers provided further information and are shown in Fig. 2. In the 19F NMR spectrum of FMA monomer, we assigned the peaks between 73 and 77 ppm to the trifluoromethyl group, the peaks between 186 and 191 ppm to the difluoromethylene group, and the peaks between 209 and 213 ppm to the

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Fig. 2. 19F spectrum of FMA monomers (a) and copolymer with FMA content of 8.24% (b).

Fig. 1. IR spectrum of acrylic copolymers with different amounts of FMA (a), VTES (b).

monofluoromethylyne group. In the 19F NMR spectrum of FMA-containing copolymer, the peaks between 72 and 76 ppm, which is assigned to trifluoromethyl group, had appeared, this can certify that FMA has participated in the copolymerization. The fact that the other two peaks did not appear was due to the low content of FMA. 3.2. Latex particle size and morphologya From the particle size data listed in Table 1, we can see that the particle sizes of all specimens are about 130 nm, and the polydispersity index were all less than 0.1 indicating that the particles exhibit a monomodal distribution. As the amount of FMA increased, the particle size had no variation basically, but the latex particle sizes increased with the amount of VTES increasing. The low polydispersity values of the samples indicated that the narrow distribution of the resulting latices, further revealing

that the second-stage monomers almost polymerized onto the surface of the core seeds and formed the shell phase. VTES is a multi-functional monomer, it contains a C@C bond and three ethoxy groups which can generate crosslinking reticular structure. That is, it acted as a crosslinker. Because of the existence of VTES, the crosslinking reaction occurred during the emulsion polymerization allowing some linear macromolecules to link and form networks among molecule chains. Moreover, the crosslinking density increased with increasing the amount of VTES, so the average particle size of latices increased with the amount of VTES increasing, but have no variation with the amount of FMA increasing. Fig. 3 shows the core–shell particle morphology. As shown, all colloidal particles existed as monomodal entities with two insignificantly different electron densities. From images a and b (Fig. 3), we can see that the particle sizes had no significant variation as the amount of FMA increased. But as the amount of VTES increased (images c and d), the particle size increased significantly, this was just in agreement with the case described by latex particle size determination. The core–shell structure was not very well distinguished in the image, probably because there was some compatibility between polyacrylate and fluorinated polyacrylate.

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Fig. 3. TEM photographs of latex particles for FMA = 0%, VTES = 0.33% (w/w) (a); FMA = 8.24%, VTES = 0.33% (w/w) (b); VTES = 0%, FMA = 4.21% (w/w) (c); and VTES = 0.66%, FMA = 4.21% (w/w) (d).

3.3. Surface properties 3.3.1. Contact angle Surface properties of polymers are usually governed by the structure and chemical composition of the outermost surface layer and, thus, are quite different from the bulk properties. Preliminary investigations of the novel polymers’ surface properties were conducted by determination of the contact angle. It is well known that the low molecular weight n-alkane is usually absorbed or solubilized on the surface of the polymers. In the case of higher molecular weight n-alkane, such as n-hexadecane, it has been accepted that the dissolution effect is negligible [22]. The contact angle of n-hexadecane is a particularly sensitive method for detecting fluorine existing on the surface of the polymers [23]. So we chose water and n-hexadecane as the wetting liquids, the water contact angle was used as criteria

for the hydrophobicity of the surface and the n-hexadecane contact angle was used as criteria for the oleophobicity of the surface. The advancing and receding contact angles of water and n-hexadecane are depicted in Figs. 4, and 5 as the function of the content of FMA and VTES, respectively. The contact angles of water and n-hexadecane droplets on the film were both enhanced significantly even with a very small amount of FMA, and there had a large difference between advancing and receding contact angles. Compared with FMA, the contact angles for VTES did not increase so much, the hysteresis for VTES was not so large, and the hysteresis had a trend of reduction increasingly. It follows from the classical Gibbs adsorption law that in multi-component systems the surface is enriched in the component with the lowest surface tension. The surfaces of films prepared with a

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Contact angle (o)

100 80 60 40 20 0 0

2

4

6

8

FMA (%) Fig. 4. Advancing (filled symbols) and receding (open symbols) contact angles of water (j) and n-hexadecane (m) as a function of the content of FMA.

110 100

Contact angle (o)

90 80 70 60

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water–film interface, while nonpolar perfluoroalkyl groups migrated to the interior of the polymers. However, the nonpolar liquid n-hexadecane interacted more strongly with hydrocarbon-type surface functionality through dispersion forces. The interaction also resulted in increased solvent penetration into the surface, reorientation of alkyl functionality toward the hydrocarbon–solid interface and pendant perfluoroalkyl groups toward the interior of the polymers. Thus, there were obvious hysteresis when subjected to contact angle measurements of water and n-hexadecane. Although the alkyl chain of FMA we used was less than seven, the fluorinated domains were in a random state of aggregation without a crystalline phase and the fluorinated chains would reorient and rearrange with the environmental change [25], the crosslinking of VTES can inhibit liquid penetration and surface reconstruction by immobilizing the surface molecules. Crosslinking would, therefore, decrease contact angle hysteresis. And as the amount of VTES increased, more and more fluorinated chains were fixed on the surface; thus, the hysteresis had a trend of reduction increasingly.

50 40 30 20 10 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

VTES (%) Fig. 5. Advancing (filled symbols) and receding (open symbols) contact angles of water (j) and n-hexadecane (m) as a function of the content of VTES.

majority of fluorine monomer would be dominated by perfluoroalkyl groups oriented toward the air interface [24]. The most important advantages of fluorinated polymers are hydrophobicity and oleophobicity. Thus, as the amount of FMA increased, the contact angles of water and n-hexadecane were both enhanced. And as the amount of VTES increased, more fluorinated chains were fixed on the surface, the contact angles of water and n-hexadecane were both enhanced, too. For contact angle hysteresis, surface rearrangement of fluorocarbon groups could be used to explain it. When the polar water contacted the surface, polar molecules in the region of the surface rearranged, allowing solvent penetration, and facilitating the migration of polar groups toward the

3.3.2. Surface free energy From the equation for the Gibbs adsorption isotherm, it can be seen that a differential in surface tension will result in a surface enrichment of the lower surface tension species [26]. This surface enrichment can be useful to design an ‘‘ideal’’ coating system that combines the best bulk properties with the optimized surface properties. The total surface free energy of solid can be calculated from the contact angles of two wetting liquids having known values of polar (cp) and dispersive (cd) components of surface energy by Fowkes’ equation as follows [23]: cL ð1 þ cos hc Þ ¼ 2ðcdS cdL Þ

0:5

0:5

þ 2ðcpS cpL Þ ;

ð4Þ

where p and d are the polar and dispersion components of each surface free energy, hc is the advancing contact angle, and cS and cL are the interfacial tensions at solid–vapor and liquid–vapor interfaces, respectively. By measurement of the contact angles on a solid surface with two liquids, which the polar and dispersion components of surface tensions are known, the total surface free energy of a solid and its components can be calculated. In this study, we used water (cdL ¼ 21:7 mN/m, cpL ¼ 51:8 mN/m at 22 C) as a polar wetting liquid and n-hexadecane (cdL ¼ 27:6 mN/m, cpL ¼ 0 mN/m) as an apolar

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Table 2 Surface energies of latex films calculated from Eq. (3)

FMA-0 FMA-5.89 FMA-8.24 VTES-0 VTES-0.33 VTES-0.66

cdL (mN/m)

cpL (mN/m)

cL (mN/m)

27.6 17.5 15.4 23.8 21.1 19.6

2.8 0.9 0.1 2.3 1.8 1.1

30.4 18.4 15.5 26.1 22.9 20.7

wetting liquid. Given in Table 1 are the polar and dispersive components and surface free energy of the latex films calculated from geometric mean approximation in Eq. (4). From Table 2, it can be seen that the surface energy of copolymer films decreased monotonically as increasing the amount of FMA and VTES in the latex particles. A small amount of fluorinated monomers induced a significant reduction of surface energy, and the lowest surface energy in our work was 15.5 mN/m. However, as the amount of VTES increased, the surface energy decreased a little. In many cases, the surface energy of random copolymers was linearly proportional to the molar fraction of their monomer units [27]. However, the degree of

fluorination influenced the surface tension in a nonlinear way, and a small amount of fluorinated monomers induced a significant reduction of surface energy mainly due to the surface segregation of fluorinated portion of the polymer chains. As the amount of VTES increased, the surface energy decreased a little due to crosslinking reaction, which could fix more fluorinated portion on the surface. However, as the amount of FMA, which was the main reason of lowering the surface energy, was quantitative, the reduction of surface energy was not so big even with the amount of VTES being increased. 3.4. Surface composition at the film surfaces In addition to the contact angle measurements, AFM was also used to reveal the fluorine enrichment at the surface. Fig. 6 shows a series of height images recorded from the film–air interface for acrylic copolymers films which were coalesced at 25 C. Depending on the FMA and VTES fraction in the copolymers, the surface morphology is varied significantly. From the height image in Fig. 6, we can see that individual particles can be distinguished. As the

Fig. 6. Height image of TM–AFM in 2 · 2 lm area: (a) FMA = 0%, VTES = 0.33% (w/w); (b) FMA = 8.24%, VTES = 0.33% (w/w); (c) VTES = 0%, FMA = 4.21% (w/w); and (d) VTES = 0.66%, FMA = 4.21% (w/w).

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amount of FMA and VTES increased, the roughness of the surface increased. This was because of the addition of FMA into the copolymers, which resulted in the formation of much rougher latex films [28]. The surface roughness played a significant role in surface properties, a slight increase of surface roughness led to larger contact angle hysteresis. From a recent report, the contact angle over 120 can be influenced by the roughness effect, and it was apparent [29]. In our work, the contact angles we have determined were all under 120, yet those samples did show appreciable hysteresis when subjected to contact angle measurements, this indicated that high hysteresis is arising from surface chemical heterogeneity and surface reconstruction, but not roughness. Fig. 7 is the corresponding phase image of Fig. 6. In the phase image, the difference between the phase angle of vibration of the free oscillating tip and the phase of the tip as it interacts with the sample surface describes the characteristics of the tip-sample force interactions. It is well known that [30] particles of brighter contrast were not detected in the phase images of the homopolymer, and in many cases for a particular choice of measurement parameters, a brighter phase contrast is expected for stiffer materials as described in the literature. In our work, the stiffer materials were assigned to fluorine-containing

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particles based on the fact that the crystalline fluorine-containing particles were more rigid. Thus, the latex of acrylic homopolymer without FMA displayed a continuous homogeneous phase. As the amount of FMA and VTES increased, the brighter fraction increased significantly. Images b–d displayed the core–shell particles with large clusters of fluorine-containing particles encapsulated by a latex matrix, which was similar to microphase separation. Apparently, the core–shell particles grouped together during drying, upon which the latex shells merged together while the cores remained intact. As the adding of FMA, more and more perfluoroalkyl groups enriched in the surface, which represented as an increment of the brighter fraction in the phase image of AFM. However, the amount of FMA was not enough to cover the entire surface, there still exist some alkyl groups. Eventually, the surface of the latex was represented as two phases. It was the same situation with VTES due to the crosslinking action, which can fix more fluorinated portion on the surface. 4. Conclusions In our work, emulsion polymerization of a variety of hydrocarbon monomers with FMA and VTES affords stable latex of core–shell acrylic

Fig. 7. Phase image of TM–AFM in 2 · 2 lm area: (a) FMA = 0%, VTES = 0.33% (w/w); (b) FMA = 8.24%, VTES = 0.33% (w/w); (c) VTES = 0%, FMA = 4.21% (w/w); and (d) VTES = 0.66%, FMA = 4.21% (w/w).

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copolymers containing fluorine enriched in the shell. The new polymers combine in a single polymer the unique properties of both fluorinated and silicated polymers. The colloidal particles exist as monomodal entities with core–shell structure. The particle sizes have no significant variation as the amount of FMA increases, but increase largely as the amount of VTES increases due to the crosslinking reaction. Both hydrophobicity and olephobicity are improved significantly by the surface enrichment of perfluoroalkyl groups as proved by contact angle and AFM measurements. The fixture of fluorine at the surface by the crosslinking reaction of VTES is the key factor for the low contact angle hysteresis. Overall, these copolymers containing fluorine and silicon provide significant advantages for coatings applications where a low surface energy is required. References [1] Mercer F, Goodman T, Wojtowicz J, Duff D. J Polym Sci Part A: Polym Chem 1992;30:1767–70. [2] Ameduri B, Boutevin B, Kostov G. Prog Polym Sci 2001;26:105–87. [3] Brinker CJ, Scherer GW. Sol–gel science: the physics and chemistry of sol–gel processing. Boston: Academic Press; 1990. [4] Parker H, Lau W, Rosenlind ES. Rohm and Haas Co., US Patent No. 6218464; 2001. [5] Lonostro P, Choi S, Ku C, Chen S. J Phys Chem B 1999;103:5347–52. [6] Thomas RR, Lloyd KG, Stika LM, Stephans LE, Magallanes GS, Dimonie VL, et al. Macromolecules 2000;33: 8828–41. [7] Linemann RF, Malner TE, Brandsch R, Bar G, Ritter W, Mu¨lhaupt R. Macromolecules 1999;32:1715–21. [8] Chen SA, Lee ST. Macromolecules 1991;24:3340–51.

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