Surface Properties of Pristine and Fluorinated Multiwalled Carbon

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Surface properties of pristine and fluorinated multiwalled carbon nanotube/poly(dimethylsiloxane) composites Fateme Irani, Ali Jannesari, and Saeed Bastani Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie3027982 • Publication Date (Web): 01 Apr 2013 Downloaded from http://pubs.acs.org on April 6, 2013

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Industrial & Engineering Chemistry Research

Surface properties of pristine and fluorinated multiwalled carbon nanotube/poly(dimethylsiloxane) composites Fateme Irani, † Ali Jannesari,† * Saeed Bastani †‡ †

Institute for Color Science and Technology, 16765-654-Tehran-Iran

‡ Centre of Excellence for Color Science and Technology, 16765-654-Tehran-Iran KEY WORDS: Poly(dimethylsiloxane); Multiwalled carbon nanotubes; Composite; Surface properties ABSTRACT Incorporation of fluorinated multiwalled carbon nanotubes (MWCNTs) into poly(dimethylsiloxane) (PDMS) was studied as an alternative method to improve its surface properties. The surface properties of PDMS matrices filled with fluorinated MWCNTs were investigated and compared to pristine MWCNT/PDMS composites. Contact angle measurements and attenuated total reflectance infrared spectroscopy revealed that the surface segregation of the fluorinated MWCNTs in PDMS led to changes in the surface chemical composition. The wetting behavior of PDMS when loaded with the fluorinated MWCNTs changed relative to unfilled samples and those filled with pristine MWCNTs. Atomic force microscopy showed that the surface roughness of the PDMS

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increased in the presence of both pristine and fluorinated MWCNTs. Determination of the surface stability of the samples in water demonstrated that the fluorinated MWCNTs were more effective than the pristine MWCNTs to stabilize the PDMS. INTRODUCTION Poly(dimethylsiloxane) (PDMS) is a type of silicone rubber that is used in fouling release coatings,1 superhydrophobic surfaces,2 medical implants 3 and microfluidic devices.4 The performance of PDMS is dictated by its surface properties, such as its low surface energy. Despite the advantages of PDMS, low water stability leading to surface reconstruction 5, 6 often limits its commercial applications. Making fluorinated moieties on the silicone surface has been widely investigated as a method to improve the surface properties and enhance the stability of PDMS in water. The use of fluorinated copolymers in silicone was extensively studied to make composite structures on the surface of PDMS.7-9 The lower surface tension of fluorinated moieties, in comparison to PDMS, can aid in air-surface segregation and fluorination of the surface. However, the attachment of fluorinated groups onto the high molecular weight polymer backbone may slow their migration to the PDMS surface.10 Introducing lower molecular weight fluorinated groups to the PDMS by a cross-linking agent is another approach to functionalize the surface.10-12 Berglin et al. 10 used semifluorinated triethoxysilane to crosslink dihydroxy-terminated PDMS. The excess cross-linking agents formed fluorinated siliceous phases which migrated to the surface and created fluorinated domains on the silicone, but these made the surface brittle.


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The disadvantages of PDMS can also be resolved by filling with small amounts of nanofillers. Nanofillers with high aspect ratios, such as carbon nanotubes (CNTs), increase the PDMS stability due to their interfacial interactions with the polymer chains. The effects of CNTs on the properties of PDMS have been studied by many researchers.13-16 Beigbeder et al. 17 showed that the incorporation of multiwalled CNTs (MWCNTs) into PDMS improves its water stability without significantly affecting its mechanical properties. The use of CNTs with fluorinated moieties was suggested as a way to change the surface properties of polymers. Deng et al. 18 utilized fluorinated MWCNTs in a poly(etherurethane) (PEU) matrix. They showed that the surface hydrophobicity of the PEU composite with small amounts of fluorinated MWCNTs increased compared to unfilled PEU due to the migration of fluorinated nanotubes to the PEU surface. Loading the PDMS matrix with fluorinated MWCNTs can be regarded as an alternative method to fluorinate the surface of PDMS and improve its surface properties. The small size of fluorinated MWCNTs can help them easily move toward the PDMS surface. This method may help to resolve the problems of other strategies that have been used for the fluorination of PDMS surfaces. The fluorination of CNTs with proper reagents creates chemically anchored fluorinated groups on their surface. Trialkoxysilane-containing fluoroalkyl side chains have attracted the interest of scientists for the fluorination of CNTs. The silanization reaction occurs between the alkoxy groups of the silane molecules and the hydroxyl groups of the CNTs, and the fluorinated chains do not react.19 In our previous study, MWCNTs were functionalized using a three steps method consisting of oxidation in an acid mixture, reduction with diisobutylaluminum hydride and silanization with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane. Fluorinated



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MWCNTs were obtained and characterized as the main product of this process. Composites of unmodified and fluorinated MWCNTs with PDMS were fabricated, and their fouling release properties were investigated.20 In this study, dihydroxy-terminated PDMS was filled with unmodified and fluorinated MWCNTs in different concentrations. The presence of fluorinated MWCNTs in PDMS was compared to the addition of unmodified MWCNTs to measure their effect on the PDMS surface properties. The gelation time of the samples was measured to evaluate the behavior of the fluorinated MWCNTs in the PDMS matrix. The effect of these two types of MWCNTs on the chemical composition and structure of the surface of PDMS was investigated by contact angle measurements, analysis of the functional groups on the surface, determinations of the critical surface energy and evaluations of the surface roughness. The water stability of the PDMS matrices filled with the two types of MWCNTs was examined by submerging samples in water for a certain number of days. EXPERIMENTAL SECTION Materials and MWCNT modification. Pristine MWCNTs (Nanocyl-Belguim) with an average diameter of 9.5 nm, an average length of 1.5 µm and a purity of 90% were used as the nanofiller without further purification. The following reagents were used for the functionalization process: sulfuric acid 95-97%, nitric acid 69%, n-hexane and toluene (Merck-Germany), diisobutylaluminum hydride (0.1 M in n-hexane) (Merck-Germany) and (heptadecafluoro-1,1,2,2tetrahydrodecyl)triethoxysilane (Fluorochem- the U. K.) with a purity of 97%.


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The MWCNTs were functionalized by oxidation in a mixture of sulfuric acid and nitric acid. Any carboxylic acid groups introduced onto the MWCNTs were then reduced to hydroxyl groups using diisobutylaluminum hydride as the reducing agent.20, 21 Fluorinated MWCNTs were obtained by the silanization of the reduced products with (heptadecafluoro1,1,2,2-tetrahydrodecyl)triethoxysilane.20 More details about MWCNT modification are given in the SUPPORTING INFORMATION. The composite matrix was composed of dihydroxy-terminated PDMS (Bluestar-France). The molecular weight and viscosity of the PDMS were 49000 g/mole and 5000 cSt, respectively. Tetraethoxysilane (TEOS, Wacker-Germany) was used as the cross-linking agent. Dibutyltin diacetate (DBTDA, Merck-Germany) was used as the catalyst. The MWCNT dispersing medium was 2-propanol (Merck-Germany). Preparation of samples. The dispersion of both the pristine and fluorinated MWCNTs in PDMS was performed according to the solution method. This procedure improves the dispersion of MWCNTs in PDMS.22 Both the pristine and fluorinated MWCNTs were dispersed separately in 2-propanol (0.2 mg/ml) by ultrasonicating the suspensions for 30 min in an ice and water bath. These suspensions were then added separately to PDMS to prepare a composite with three different weight percentages of MWCNTs (0.05 wt.% (R05), 1.0 wt.% (R1) and 2.0 wt.% (R2) pristine MWCNT coatings and 0.05 wt.% (F05), 1.0 wt.% (F1) and 2.0 wt.% (F2)). More details about MWCNT concentrations and sample coding are given in the SUPPORTING INFORMATION. The prepared mixtures were stirred at 50 ˚C to completely evaporate the alcohol. The cross-linking agent, TEOS, was then added to the mixture and stirred for 15 min. The weight ratio of PDMS to TEOS was 5 to 1 for all samples. The catalyst, DBTDA, 1 wt% of the total weight of the sample, was



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added, and the mixture was stirred for 1 min. Additionally, a blank sample without MWCNTs was prepared according to the same procedure. All samples were cured at 24±1 ˚C and 50% relative humidity for 3 days. Characterization. Gelation time measurements were performed by mixing the blank sample at 60 rpm and recording variations in the torque with time. This was carried out using a constant speed mixer (Heidolph Brinkmann 03690090- Germany) for mixing the sample. Attenuated total reflectance infrared spectroscopy (ATR-IR, Perkin Elmer Spectrum Onethe U.S.A.) was performed from 650 to 4000 cm-1 at a resolution of 4 cm-1. ATR-IR specimens were prepared by casting into rectangular molds (140×40×1 mm). The sessile drop method was used to measure the static contact angle (SCA). A laboratory made contact angle goniometer was utilized to determine the SCA (Figure 1). The SCAs were measured at 5 different points on the surface of each sample with deionized water, cyclohexane, ethanol and n-hexane. For this test, the specimens were prepared by applying the composite materials on degreased aluminum plates (20×20×1 mm) through a dipping process. The contact angle images of the drops were captured less than 10 s after placing a 5 µl drop23 on the surface to avoid any evaporation effect in the droplets. The contact angle measurements were analyzed using Drop Analysis software. Here, the averages of the resulting data with ±1˚ error have been reported.


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Figure 1. Laboratory-made system to measure the SCA The critical surface energy of the samples was determined by using Zisman plots with the SCA results of each sample. Scanning electron microscopy (SEM, VEGA/TESCAN-the Czech Republic) was employed to visualize the surfaces of the MWCNT/PDMS composites (15 KV). The samples were prepared for SEM by coating a layer of gold on their surface. Atomic force microscopy (AFM) in tapping mode (Dualscope/ Rasterscope C26, DMEDenmark) was used to study the surface structure of the samples. The composites on degreased aluminum plates were analyzed with silicon AFM tips (Mikromasch NSC16) in air and at 24±1 ˚C and 30% relative humidity. No digital leveling was applied to the AFM images. The roughness of the surface is reported as both the average roughness (Ra) and the root mean square (RMS) roughness. The Ra is the average of the Z values in the vertical direction from mean line (Zave) to each point, as calculated by Equation (1). The RMS roughness is the standard deviation of the Z values and calculated according to Equation (2). In these equations, n is the number of points in a given area.24



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Ra =

(1)

RMS =

(2)

Dynamic contact angles (DCAs) were measured by the Wilhelmy plate method using a dynamic surface tensiometer (Krüss K100-MK2-Germany). The coated aluminum plates were immersed in deionized water (γ = 72.6 mN/m) and withdrawn at a rate of 6 mm/min. The net force on each sample versus the distance curve (FDC) was plotted by the tensiometer software during the measurement process. The DCAs were calculated according to Equation (3):25 (3) Where F is the applied net force on the sample in each position obtained from the FDCs, γlv is the surface tension of water, P is the perimeter of the samples exposed to water, and θ is the DCA. The DCAs are defined by the advancing contact angle (θadv) and the receding contact angle (θrec) when the sample enters and exits the water, respectively. The θadv and θrec measurements were repeated at least three times by immersing three specimens from each sample. After each measurement, the deionized water was refreshed because other studies have showed that water contaminated with PDMS during the DCA measurements has an effect on the FDC.12 The averages of the measured data were reported with an error of ±1˚. The contact angle hysteresis (CAH) of the samples was determined using Equation (4).25 CAH = θadv – θrec

(4)


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The surface stability of the samples against water was investigated by immersing the composites in deionized water for 20 days. The samples were then removed, washed with deionized water and dried at 24±1 ˚C. The SCA of deionized water on the immersed samples was measured to determine the difference between the water contact angle before and after water immersion. The contact angle measurements were performed within approximately one minute of removing the samples from water. The reported results from this test were the averages of five points from each sample with an error of ±1˚. RESULTS AND DISCUSSION Gelation time. The gelation time of a sample can be defined as the point that the viscosity of the sample increases drastically.26 In this study, investigation of the variations in viscosity was based on the change in force required to mix the sample blank. The required force was determined by using a mixer that could measure the applied torque required for mixing the sample at a constant speed. Therefore, changes in torque over time while mixing at a constant speed were recorded to determine the gelation time. The measured changes in torque with time for the blank sample are shown in Figure 2. The torque of mixing does not change considerably when mixing PDMS and TEOS in the first 15 min. This indicates that a reaction between the PDMS and TEOS did not significantly occur and that the viscosity of the sample was constant over this time period. After 15 min the DBTDA was introduced into the mixture and the torque of mixing gently rises for 7 min, at which point it increases markedly up to the gelation point of the sample. This time was considered to be the gelation time of the sample.



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Figure 2. The change in torque of the blank sample with mixing time ATR-IR spectroscopy. Figure 3 shows the ATR-IR spectra of the blank, R2 and F2 samples. The asymmetric and symmetric stretching modes of methyl groups appear at 2962 and 2910 cm-1, respectively. The bands at 1256 and 1408 cm-1 are attributed to the bending vibrations of the methyl groups.22, 27 The broad band from 1013 to 1100 cm-1 represents the asymmetric stretching vibration of Si–O–Si groups.27 All of these bands are associated with the functional groups of the PDMS chains. The IR bands of PDMS do not change in the presence of pristine MWCNTs, according to the ATR-IR spectrum of sample R2. This is attributed to the coverage of the pristine MWCNTs by a layer of cross-linked PDMS.22 A new band located at 1210 cm-1 in the ATR-IR spectrum of sample F2 is ascribed to the stretching vibration of –CF groups.19, 28 This reveals the presence of fluorinated groups on the surface of sample F2. The fluorinated MWCNTs had a lower surface energy than the PDMS because of the covalently attached fluorinated groups on their sidewalls. This low surface energy might promote the migration of the fluorinated nanotubes to the surface of the samples.18 A portion of the fluorinated MWCNTs were able to migrate to the PDMS surface during curing and before the gelation of the PDMS. This resulted in a change in the chemical composition of the silicone surface. In other words, surface segregation of the


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fluorinated MWCNTs resulted in a type of fluorinated silicone structure on the PDMS. SEM images of the surface morphology and schematic representations of the cross-sections of the PDMS samples filled with the pristine and fluorinated MWCNTs are shown in Figure 4.

Figure 3. ATR-IR spectra of the blank, R2 and F2 samples



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Figure 4. SEM images of the surface of the samples and schematic representations of their cross sections; a: filled with the pristine MWCNTs (sample R2), b: filled with fluorinated MWCNTs (sample F2) SCA. The SCAs on the surface of the samples coated on aluminum plates were measured by the sessile drop method. Of the liquids used, only n–hexane wetted all the surfaces completely, and the SCAs were approximately zero for all samples with this liquid. The SCAs of deionized water on all of the samples were greater than 100˚, proving the hydrophobic nature of their surfaces. There was no significant difference between the SCAs


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of deionized water on samples R05 and R1 and that of the blank. In sample R2, an increase in the SCA from 108˚ to 112˚ with the incorporation of 0.2 wt% of the pristine MWCNTs was observed. The SCAs of deionized water on samples F05, F1 and F2 were approximately 5˚ larger than the blank sample. The enhancement of the SCAs on the samples containing the fluorinated MWCNTs can be attributed to a change in the nature of the surface of these samples due to the surface migration of a portion of the fluorinated MWCNTs. The presence of pristine MWCNTs had no considerable effect on the SCAs of ethanol and cyclohexane on the surfaces of the samples, compared to the blank sample. The SCAs of ethanol and cyclohexane increased on the samples filled with the fluorinated MWCNTs. This indicates that the migration of the fluorinated MWCNTs to the surface of the samples made them more hydrophobic and lipophobic than pure PDMS. The SCAs of deionized water, ethanol and cyclohexane on the samples did not change significantly with increased loading of fluorinated MWCNTs. From these results, it can be concluded that increasing the weight percentage of the fluorinated MWCNTs did not lead to any further surface segregation. The low surface energy of the fluorinated MWCNTs is a thermodynamic factor in the migration of the MWCNTs to the surface. Kinetic factors, such as the gelation time, also have important impacts on the surface segregation of the fluorinated MWCNTs. The gelation time of the samples is a vital time for surface segregation because nanotubes cannot move in a gelled polymer matrix. The gelation time of PDMS in this study was approximately 7 min, as mentioned above. This suggests that during this short time, only a small amount of the fluorinated MWCNTs near to the surface of sample could move



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upward to the surface. Details of the SCA results are given in the SUPPORTING INFORMATION. Critical surface energy. The critical surface energy of the blank sample was 18.15 mJ/m2. Inclusion of the pristine MWCNTs in the samples did not affect the critical surface energy of PDMS, as confirmed by ATR-IR. The critical surface energies of samples F05, F1 and F2 were less than that of the blank (approximately 3.5 mJ/m2) due to the creation of a fluorinated silicone structure on the surface of the samples. The influence of the amount of fluorinated MWCNTs on the critical surface energy of the samples was negligible according to the SCA results. Details of the critical surface energy results are given in the SUPPORTING INFORMATION. AFM. The topography of the sample surfaces was visualized by AFM imaging. AFM tapping mode images of the blank, R1, R2 and F2 samples are illustrated in Figure 5. The surface of the blank sample was relatively smooth (Ra= 2 nm, RMS= 4 nm). Incorporation of 0.1 wt% of pristine MWCNTs into the PDMS had a remarkable impact on the surface roughness of sample R1. The Ra and RMS values measured for the R1 surface were 18 and 24 nm, respectively. Increasing the weight percentage of the MWCNTs to 0.2 wt% for sample R2 led to an increase in the surface roughness (Ra= 29 nm, RMS= 36 nm). This increase in the surface roughness can be attributed to the aggregation of the nanotubes, as shown in the schematic image in Figure 4. The size of the nanotube aggregates increased with increasing MWCNT content, and this aggregation might cause the increase in roughness from sample R2 compared to sample R1.


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According to the Wenzel theory,29 an increase in the surface roughness of a hydrophobic surface leads to an increase in the surface hydrophobicity. Therefore, this may be the main reason for the 4˚ increase in the SCA of deionized water on the surface of sample R2 relative to the blank. The SCA of deionized water on the surface of sample R1 was comparable to that of the blank, even though it had a higher roughness than the blank. This may be related to differences in the size and arrangement of the roughness elements on the surface of samples R1 and R2. The distribution plots of the roughness on the surfaces of R1 and R2 are shown in Figure 6. It can be seen that both the distance between the peaks and valleys and the average surface roughness values of the R2 surface are larger than those of the R1 surface. The width of a peak in a given area on the surface of R2 is approximately 1.5 times wider than that of R1. It seems that the surface roughness of R1 was not large enough to change the surface hydrophobicity considerably. In accordance with the AFM data, the Ra and RMS of sample F2 are 21 and 26 nm, respectively. The roughness values of sample F2 were less than those of R2 due to a reduction in the size of the aggregates of the fluorinated MWCNTs in sample F2. The anchor of the fluorinated functional groups on the sidewall of the MWCNTs made the density higher than the density of the unmodified nanotubes. Therefore, 0.2 wt% of the fluorinated MWCNTs had less volume in comparison to 0.2 wt% of the pristine MWCNTs, and consequently, the aggregated nanotubes for the fluorinated MWCNTs were confined. Phase contrast images of the surfaces of the samples are also presented in Figure 5. These images can be used to visualize different materials on the surface. The phase contrast images of the blank, R1 and R2 samples are homogenous, indicating that the surfaces of these samples were made of one phase. This was also confirmed by the ATR-IR spectra and



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the critical surface energy data. The phase contrast image of sample F2 shows two different regions on the surface. The lighter parts display the regions with higher modulus.12 These regions are the rough zone on the surface, as seen in the topographic image, illustrating the aggregated fluorinated MWCNTs that have a higher modulus than PDMS. These images demonstrate that the fluorinated MWCNTs partially migrated to the surface and increased the surface fluorination and roughness.


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Figure 5. AFM tapping mode images of the blank, R1, R2 and F2 samples; Left figures: topographic images; Right figures: phase contrast images

Figure 6. Distribution of roughness on the surface of samples; Top: R1; Bottom: R2 DCA. The resulting FDCs of the blank, R1, R2 and F2 samples are shown in Figure 7. The DCAs, and consequently the CAH values, of the blank and R05 samples showed no significant difference. However, the addition of 0.1 wt% of the pristine MWCNTs to PDMS led to an increase in the θrec in comparison to the blank, but did not influence the θadv. The θadv increased to 121˚ (from 114˚ for the blank), while the θrec decreased to 79˚ (from 83˚ of the blank) when 0.2 wt% of the pristine MWCNTs were incorporated into the PDMS (sample R2). According to the Johnson and Dettre theory 30, 31, water cannot move easily on the surface of R2 because of the hindering effects of the roughness. A drop must leap over the crests of the surface leading to an increase in the θadv. The valleys on the rough surface of R2 also disturb the advance of the water. In other words, the liquid has to wet more parts of the surface, and therefore θrec decreased significantly. The CAH



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decreased to 24˚ for sample R1 and increased to 42˚ for sample R2 compared to the blank (31˚). Both the θadv and θrec of samples F05, F1 and F2 were 7˚ and nearly 8˚ larger than those of the blank, respectively. This is attributed to the presence of fluorinated moieties on the surfaces of these samples that increase the hydrophobicity of these surfaces. The CAH of the samples filled with the fluorinated MWCNTs was comparable with that of the blank. Details of the DCA results are given in the SUPPORTING INFORMATION. The results of the DCA measurements demonstrate the impact of the pristine and fluorinated MWCNTs on the wetting behavior of the PDMS composites. The presence of the pristine MWCNTs in the PDMS increased the roughness, which restricted the movement of water along the surface. The incorporation of 0.2 wt% of the pristine MWCNTs into the PDMS was a meaningful value in which the wetting behavior of PDMS composite observably changed. The presence of the fluorinated MWCNTs in the PDMS led to a more hydrophobic nature than unfilled PDMS. This can help reduce the drag between water and the surface during water procession on the samples.


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Figure 7. FDCs for the blank, R1, R2 and F2 samples



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Surface stability of samples in water. The study on surface stability of the prepared samples in water was performed by keeping them in deionized water for 20 days. The SCAs of deionized water on the samples before and after water immersion are shown in Table 1. The SCA of deionized water on the blank sample decreased, after water immersion. This result can also be observed for sample R05. The SCAs on samples R1 and R2 after water immersion were similar to each other compared to that of the blank. A type of surface rearrangement of PDMS occurs upon water exposure. The polar groups in the PDMS matrix shift to the surface and replace the non-polar functionalities. This leads to the development of a more hydrophilic PDMS surface after water submersion.5 The presence of pristine MWCNTs in the PDMS matrix and their high interfacial interaction improved the stability of PDMS against water by retarding the movement of polar groups to the surface. The reduction of the water contact angles on the fluorinated silicone samples was remarkably less than that observed for the blank. The existence of fluorinated groups on the silicone surface might lead to surface reinforcement and prevent its reconstruction. This is observed for the water stability of the PDMS based samples fabricated with smaller amounts of the fluorinated MWCNTs in contrast to the pristine nanotubes. It can be inferred that the fluorinated MWCNTs were more effective than the pristine MWCNTs for the stabilization of the PDMS surface. This is associated with the migration of a portion of the fluorinated MWCNTs to the PDMS surface and the creation of fluorinated silicone structures on the surface. Table 1. SCAs of deionized water on the samples before and after 20 days immersion in water (±1˚)


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Sample code

SCAs before immersion (˚)

SCAs after immersion (˚)

blank

108

99

R05

109

100

R1

109

103

R2

112

109

F05

113

109

F1

113

111

F2

112

112

CONLUSIONS The addition of pristine and fluorinated MWCNTs in MWCNT/PDMS composites were examined for three weight percentages of 0.05, 0.1 and 0.2 wt% MWCNTs to study their effects on the surface properties of the composites. According to ATR-IR analysis, a crosslinked layer of PDMS covered the pristine MWCNTs, and as a result the critical surface energy of their composites did not change in comparison to unfilled PDMS. However, the hydrophobicity of samples filled with 0.2 wt% of the pristine MWCNTs increased and changes in the wetting behavior were also observed with respect to the unfilled PDMS due to a remarkable increase in the surface roughness. The migration of a portion of the fluorinated MWCNTs to the PDMS surface led to the formation of a fluorinated silicone structure, even with just a 0.05 wt% incorporation of the fluorinated MWCNTs. The



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presence of fluorinated moieties on the PDMS surface decreased the critical surface energy and increased its roughness. The SCAs and DCAs showed that the fluorinated silicone samples were more hydrophobic and lipophobic than the other prepared samples. The surface properties of the fluorinated silicone samples were independent of the fluorinated MWCNT content. This was attributed to the short gelation time of the samples, which confined the surface segregation of the fluorinated MWCNTs. The water stability of the samples loaded with pristine MWCNTs increased in comparison to the unfilled PDMS due to interactions between the nanotubes and the silicone chains. Filling the PDMS matrices with the fluorinated MWCNTs made the surfaces more stable in water because of the fluorinated silicone structure of the surface retarding reconstruction. The results show that the incorporation of fluorinated MWCNTs into PDMS, even in small amounts, can be an acceptable method to improve its surface properties and stability.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Tel: +98-21-22956126 Fax: +98-21-22947537 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. † These authors contributed equally.


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ACKNOWLEDGMENT The authors would like to acknowledge with gratitude PARS PAMCHAL CHEMICAL CO. who kindly supported this work financially. SUPPORTING INFORMATION AVAILABLE Details of MWCNT modification, Table of sample coding, details of SCAs, critical surface energy and DCAs. This material is available free of charge via the Internet at http://pubs.acs.org. REFERENCES (1)

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Surface Properties of Pristine and Fluorinated Multiwalled Carbon

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