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Langmuir 1999, 15, 8052-8058
Synthesis and Characterization of Submicrometer-Sized Polypyrrole-Polystyrene Composite Particles D. B. Cairns and S. P. Armes* School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, East Sussex BN1 9QJ, U.K.
L. G. B. Bremer PAC-MC, DSM Research, 6160 MD, Geleen, The Netherlands Received April 9, 1999. In Final Form: July 14, 1999 A conducting polymer, polypyrrole (PPy), has been deposited from aqueous media onto a submicrometersized poly(ethylene glycol)-stabilized polystyrene (PS) latex. Deposition experiments were carried out at two different initial pyrrole concentrations, and the latex concentration was systematically adjusted in order to control the final conducting polymer loading. Transmission electron microscopy studies showed that at a pyrrole concentration of 5.0 × 10-3 M the PPy had deposited onto the latex as discrete PPy nanoparticles of 20-30 nm diameter. These nanoparticles act as a bridging flocculant or binder, leading to heteroflocculation of the PS latex. Thus the expected “core-shell” morphology was not observed. Pressed pellet conductivity measurements indicated relatively low conductivities (∼10-2 S cm-1) for the composites at PPy loadings less than 20 wt %. This is in contrast to earlier studies (Lascelles, S. F.; Armes, S. P. J. Mater. Chem. 1997, 7, 1339) of micrometer-sized PPy-coated PS latexes which exhibited conductivities similar to PPy bulk powder (∼1 S cm-1) even at PPy loadings as low as 5 wt %. The relative colloid stabilities of the PPy-PS composites were assessed by disk centrifuge photosedimentometry (DCP) studies. For PPy loadings up to 16.6% or lower a reasonable degree of colloid stability was retained, but the PS latex particles were present as stable colloidal microaggregates, which is in good agreement with scanning electron microscopy studies. In contrast, DCP analysis confirmed that a PPy-PS composite prepared using a relatively low latex surface area and a pyrrole concentration of 5 × 10-4 M comprised mainly singlets, with a much smaller contribution from doublets, triplets, and higher aggregates.
Introduction In recent years considerable research activity has centered on relatively air stable organic conducting polymers (OCPs) such as polypyrrole (PPy) and polyaniline (PANi). In principle such materials offer metallic-like conductivities with the processability and versatility of organic polymers. However, due to the high degree of conjugation required for such conductivities OCPs are often rather intractable materials in practice. To improve the processability of these materials various groups have reported the synthesis of sterically stabilized dispersions of PPy particles with submicrometer dimensions.1-4 where the PPy “core” is surrounded by an outer layer of absorbed, solvated water-soluble polymer which acts as a steric stabilizer. Suitable stabilizers include methyl cellulose, poly(N-vinyl pyrrolidone), poly(vinyl acetate), poly(ethylene oxide) and poly(vinyl methyl ether). Several research groups have reported the chemical synthesis of conducting polymer-coated particles where * To whom correspondence should be addressed. (1) (a) Bjorklund, R. B.; Liedberg B. J. Chem. Soc., Chem. Commun. 1986, 1293. (b) Armes, S. P.; Vincent, B. J. Chem. Soc., Chem. Commun. 1987, 288. (c) Armes, S. P.; Miller, J. F.; Vincent, B. J. Colloid Interface Sci. 1987, 118, 410. (2) (a) Cawdrey, N.; Obey, T. M.; Vincent, B. J. Chem. Soc., Chem. Commun. 1988, 1189. (b) Epron, F.; Hendry, F.; Sagnes, O. Macromol. Chem. Macromol. Symp. 1990, 35/36, 527. (c) Odegard, R.; Skotheim, T. A.; Lee, H. S. J. Electrochem. Soc. 1991, 138, 2930. (d) Digar, M. L.; Bhattacharyya, S. N.; Mandal, B. M. J. Chem. Soc., Chem. Commun. 1992, 18. (3) (a) Armes, S. P.; Aldissi, M.; Agnew, S. F. Synth. Met. 1989, 28, 837. (b) Armes, S. P.; Aldissi, M.; Agnew, S. F. Polymer 1990, 31, 569. (c) Armes, S. P.; Aldissi, M.; Agnew, S. F. Synth. Met. 1990, 37, 137. (4) Armes, S. P.; Aldissi, M.; Idzorek, G. C.; Keaton, P. W.; Rowton, L. J.; Stradling, G.; Collopy, M. T.; McColl, D. B. J. Colloid Interface Sci. 1991, 141, 119.
the “core” consists of a nonconducting particulate material. Garnier and co-workers polymerized pyrrole using chemical oxidants such as FeCl3 in the presence of commercial sulfonated PS latexes to obtain PPy-PS composites.5 Similarly, Yamamoto’s group6 coated carboxylated styrene-butadiene-methacrylate latex particles with PPy, PANi, or poly(3-methylthiophene). The oxidant was H2O2/ HBr with a catalytic amount of Fe3+, which was apparently adopted in order to reduce the chance of electrolyte-induced flocculation of the anionic latex particles. The resulting conducting polymer-coated particles were claimed to be colloidally stable with respect to aggregation, although no experimental evidence was given to support this. Inorganic oxide particles such as hematite and ceria have been utilized as particulate oxidants for pyrrole polymerization by Partch and co-workers at Clarkson.7 This approach ensured that polymerization occurs exclusively at the surface of the particles and results in the formation of PPy-inorganic oxide particles. Relatively low conductivities were reported; this is almost certainly due to the relatively high temperature selected for the pyrrole polymerization. The particles were colloidally unstable unless a polymeric stabilizer such as poly(vinyl alcohol) was added to the solution. Workers at DSM Research have recently shown that conventional sterically stabilized latex particles can be coated with a thin layer of PPy or PANi to form conducting polymer-coated latexes which retain reasonable colloid (5) Yassar, A.; Roncali, J.; Garnier, F. Polym. Commun. 1987, 28, 103. (6) Liu, C. F.; Maruyama, T.; Yamamoto, T. Polym. J. 1993, 25, 363. (7) Partch, R.; Gangolli, S. G.; Matjevic, E.; Cai, W.; Arajs, S. J. Colloid Interface Sci. 1991, 144, 27.
10.1021/la990442s CCC: $18.00 © 1999 American Chemical Society Published on Web 09/14/1999
Polypyrrole-Polystyrene Composite Particles
Figure 1. Schematic representation of the deposition of an ultrathin PPy overlayer onto a sterically stabilized low Tg latex particle. Note that the PPy resides inside the steric stabilizer layer.
stability in aqueous media6,7 (see Figure 1). The use of a chemically grafted nonionic polymeric stabilizer such as poly(ethylene glycol) was required to produce stable colloidal dispersions at high Fe3+ concentrations. Some evidence for the “core-shell” morphology was obtained by transmission electron microscopy (TEM); this observation was supported by aqueous electrophoresis and dielectric measurements. The conductive polymer is believed to be deposited onto the surface of the latex particles within the steric stabilizer layer; thus colloid stability is retained. The DSM group has concentrated on low Tg latexes such as polyurethane, poly(vinyl acetate), and alkyd resins, which all show good film-forming properties at ambient temperatures. Films prepared from the composite particles exhibit useful conductivity and both anticorrosion and antistatic applications are being evaluated. The PPy-polyurethane latex is now marketed under the tradename ConQuest. In recent follow-up studies to the DSM work, Lascelles and co-workers successfully coated micrometer-sized poly(N-vinylpyrrolidone)-stabilized PS latexes with PPy.8-12 Solid-state conductivities were as high as 2 S cm-1 at PPy loadings as low as 5.1% by mass (3.0 vol. %). This behavior was attributed to the rigidity of the high Tg PS core at ambient temperature.11 The focus of the current paper is the synthesis and characterization of the analogous, submicrometer-sized PS-PPy composites. This system was expected to be a good model for the film-forming conductive latexes being developed by DSM. Moreover, preliminary studies in collaboration with Burchell’s group at the University of Kent have shown that conducting polymercoated latexes have some potential as model projectiles for hypervelocity impact measurements.13 Experimental Section Materials. Styrene (Aldrich) was purified by passing through a column of activated alumina to remove the inhibitor. Potassium persulfate (KPS) and sodium dodecyl sulfate (SDS) were obtained from BDH and used without further purification. Monomethoxycapped poly(ethylene glycol) methacrylate (PEG) with Mw ) 2000 and Mw/Mn ) 1.10 was obtained from Laporte Specialities, Hythe, U.K., and was used as supplied. Pyrrole (BASF) was purified by passing through a column of activated basic alumina and stored in the absence of light at 4 °C prior to use. The FeCl3‚6H2O oxidant was obtained from Aldrich and used without further purification. (8) Wiersma, A. E.; Steeg, L. M. A.; Jongeling, T. J. M. Synth. Met. 1995, 71, 2269. (9) Wiersma, A. E.; Steeg, L. M. A. Europ. Pat. Applcn. 93202714.7 1993. (10) Armes, S. P.; Lascelles, S. F. Adv. Mater. 1995, 7, 864. (11) Lascelles, S. F.; Armes, S. P. J. Mater. Chem. 1997, 7, 1339. (12) Lascelles, S. F.; Armes, S. P.; Zhdan, P. A.; Greaves, S. J.; Brown, A. M.; Watts, J. F.; Leadley, S. R.; Luk, S. Y. J. Mater. Chem. 1997, 7, 1349. (13) Burchell, M. J.; Cole, M. J.; Lascelles, S. F.; Khan, M. A.; Barthet, C. B.; Wilson, S. A.; Cairns, D. B.; Armes, S. P. J. Appl. Phys. D 1999, 32, 1719.
Langmuir, Vol. 15, No. 23, 1999 8053 PS Latex Synthesis. The PS latex was synthesized using a slight modification of the procedure described by Satgurunathan and Ottewill.18 Briefly, SDS (200 mg) and deionized water (150 mL) were added to a three-necked round-bottom flask. This solution was heated with stirring to reach 80 °C. Styrene monomer was passed through a neutral alumina column. The purified monomer (20 g) was added to the solution and emulsified for 20 min with stirring. The KPS initiator (200 mg, 1 wt % based on monomer mass) dissolved in water (10 mL) was then added. After 4 h a solution of PEG (5.0 g in 30 mL of water) and a further charge of KPS (200 mg in 10 mL of water) were added to the reaction solution. The polymerization was allowed to continue for a further 16 h at 80 °C. The resulting latex was dialyzed for 2 weeks against deionized water. The dialyzate was changed every 24 h. PS Latex Characterization. The Quantachrome Nova-100 BET surface area analyzer was used to determine the uncoated latex surface area by physisorption of nitrogen. The absorbed gas volume is calculated by measuring the pressure change resulting from adsorption of a known volume of gas (nitrogen). The physisorption of nitrogen by a sample is measured at four relative pressures (P/Po) ranging from 0.05 to 0.35, which are within the linear region of the BET data.14 Po is the saturated vapor pressure of nitrogen (795 mmHg). The freeze-dried latex (1.0 g) was outgassed at 40 °C overnight. The temperature used during the outgassing procedure must be well below the Tg of latex in order to prevent particle coalescence, which would otherwise reduce the measured sample surface area.15 Helium pycnometry was used to assess the densities of PS, PEG, and the dried PS latex, which were found to be 1.05, 1.21, and 1.09 g cm-3, respectively. The particle size distribution, colloid stability, and particle size of the latex were determined using disk centrifuge photosedimentometry (DCP). All measurements were carried out using a Brookhaven BI-DCP instrument, operating in the line start mode. Samples for DCP analysis were prepared by adding a few drops of the aqueous latex to a 3 mL 1:2 v/v % methanol-water mixture. The centrifugation rate was 15 000 rpm, which corresponded to an analysis time of 15 min. TEM (Hitachi 7100 instrument) and scanning electron microscopy (SEM) (Leica Stereoscan 420 instrument) studies on the dried latexes were also carried out. The stabilizer content of the dissolved PS latexes was determined using 1H NMR spectroscopy (CD2Cl2 solvent, 250 MHz instrument). PPy Deposition Experiments. The initial uncoated PEGstabilized PS latex is abbreviated to PS-PEG. The composites prepared by the deposition of PPy on the PEG-stabilized PS latex are abbreviated to PS-PEG-PPy(X), where X is the PPy mass loading. For example, the PS-PEG latex onto which 28.1% PPy was deposited is abbreviated to PS-PEG-PPy(28.1). The abbreviation “PS-PEG-PPyLSA” refers to a PS-PEG latex coated with PPy using both a low latex surface area and also a reduced pyrrole concentration (see experiment 11 in Table 1). Preparation of the PS-PEG-PPy(X) Series. FeCl3‚6H2O (0.454 g) was dissolved in a stirred aqueous latex dispersion (0.8-6.2% solids by mass in 15 mL) in a screw-cap bottle. Pyrrole monomer (0.040 mL) was then added via syringe, and the polymerization was allowed to proceed for 24 h. The resulting black dispersions were purified by repeated centrifugation/ redispersion cycles; successive supernatants were decanted and replaced with deionized water in order to remove the unwanted inorganic byproducts (FeCl2 and HCl) produced during the pyrrole polymerization. Preparation of PS-PEG-PPyLSA. The above protocol was used except that FeCl3‚6H2O (0.908 g) was dissolved in a stirred aqueous latex dispersion (400 mL at 0.40% solids) in a screw-cap bottle, prior to the addition of pyrrole monomer (0.10 mL) via syringe. The resulting PS-PEG-PPy dispersions were centrifuged (the centrifugation rate ranged from 4000 to 12000 rpm and was dependent on the PPy loading and degree of aggregation) and were redispersed in water (this centrifugation/redispersion cycle was repeated four times in order to remove excess (in)organic byproducts such as Fe(II) salts and pyrrole monomer). (14) Berry, G. C.; Fox, T. G. Adv. Polym. Sci. 1967, 5, 261. (15) Sao, K. P.; Samantaray, B. K.; Bhattacherjee, S. J. Appl. Polym. Sci. 1994, 52, 1917.
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Table 1. Effect of Varying the PS Latex Surface Area on the PPy Loading and Colloidal Stability of the PS-PEG-PPy Composites expt noa
total latex surface area (m2 g-1)
theoretical PPy loading (% by mass)
actual PPy loading (% by mass)b
calculated PPy overlayer thicknessc (nm)
relative colloid stability by DCP
1 2 3 4 5 6 7 8 9 10 11
7 13 15 19 20 24 27 36 49 93 4
40.0 27.5 24.0 20.7 19.5 17.0 15.5 11.8 9.0 5.0 10.0
40.6 28.1 24.9 20.0 19.1 17.6 16.6 10.7 8.7 4.2 4.2
9.1 5.0 4.7 3.6 3.6 3.1 2.9 1.8 1.5 0.7 0.7
precipitate precipitate precipitate flocculated flocculated flocculated stable (aggregates) stable (aggregates) stable (aggregates) stable (aggregates) stable (mainly singlets)
a The pyrrole monomer concentration was 5.0 × 10-3 M for experiments 1-10 and 5.0 × 10-4 M for experiment 11. b Determined by comparing nitrogen contents to that of PPy bulk powder. c Calculated using eq 2 (see text).
Characterization of PS-PPy Composites. Chemical Composition. After cleanup, all PS-PPy composites and the uncoated PS-PEG latex were oven-dried overnight at 60 °C. CHN microanalyses were carried out at an independent laboratory (Medac Ltd. at Brunel University, U.K.). FTIR spectra of latex composites dispersed in KBr disks were recorded using a Nicolet Magna Series II spectrometer (64 scans, 4 cm-1 resolution). Conductivity Measurements. Each PS-PPy composite was oven-dried at 60 °C in air overnight. Pressed pellet conductivities were determined using the conventional four-point probe technique at room temperature.
Results and Discussion The particle diameter of the uncoated PS latex was determined by BET measurements and scanning electron microscopy (SEM), TEM, and DCP studies. BET analysis allows the specific surface area (As) of the latex to be calculated from the total latex surface area of a known mass of latex. The As for the uncoated PS-PEG latex was determined to be 43 m2 g-1. The number-average particle radius r (in nm) and hence the number-average diameter (Dn) can then be obtained from eq 1
r ) 3000/(AsF)
(1)
where F is the particle density in g m-3. Dn was calculated to be 129 nm by this method. SEM and TEM studies on the uncoated PS-PEG latex (not shown) indicate that the particles have a smooth spherical morphology, a relatively narrow size distribution, and a Dn of approximately 129 nm. Previous studies on sterically stabilized 1.8 µm PS particles showed DCP to be an effective technique to determine their mean particle size, which is expressed as the weight-average diameter (Dw).11 The steric stabilizer used in this earlier work was poly(N-vinylpyrrolidone), which has a hydrodynamic diameter of 20-30 nm in aqueous media.16 Thus, the contribution of this solvated steric stabilizer layer to the overall hydrodynamic radius of the particles (ca. 900 nm) was assumed to be negligible. Hence the particle density used for DCP studies was 1.05 g cm-3, i.e., the density of the dried PS latex as determined by helium pycnometry. This assumption can be confirmed by calculation: if the density of the solvated steric stabilizer layer in aqueous media is taken to be 1.00 g cm-3, it follows that the 20 nm solvated “corona” contributes only 6% of the total mass of a 1.8 µm particle. (16) Yamamoto, T.; Liu, C.; Moon, D.; Maruyama, T. Polym. J. 1993, 25, 775.
Thus, the contribution of the solvated steric stabilizer layer to the overall latex density is negligible. As a result, the particle diameter obtained by DCP using a latex density of 1.05 g cm-3 was in good agreement with SEM, TEM, and BET measurements.11 However, the latex discussed in this work consists of much smaller PEG-stabilized PS particles. The root mean square thickness, δ, of terminally grafted PEG chains of the same molecular weight on a submicrometer-sized PS latex was reported to be 3.6 nm by Cosgrove and Ryan17 using small angle neutron scattering (SANS). Since SANS is known to be relatively insensitive to the longer steric stabilizer “tails”, we estimate the hydrodynamic layer thickness to be around 5.0 nm. Thus the overall hydrodynamic diameter of the PS-PEG particles used in this work is approximately 139 nm (i.e., 129 nm for the nonsolvated latex core and an additional 10 nm contribution from the solvated PEG stabilizer layer). A similar latex density calculation was carried out as described above for the micrometer-sized PS latex, and the contribution of the solvated steric stabilizer “corona” to the overall particle mass was found to be 19%. Consequently, the effective density of the submicrometer-sized PS latex in aqueous media was calculated to be 1.04 g cm-3. At first sight this value is close to the density of PS latex (1.05 g cm-3). However, the latter density significantly underestimates the true Dw. This is because the DCP technique requires a knowledge of the density difference (buoyancy factor) between the particles and the spin fluid. In this case the spin fluid is water, which has a density of 1.00 g cm-3. Thus using a density difference of 0.04 rather than 0.05 leads to a significant increase in the particle diameter. Using the corrected density of 1.04 g cm-3 in the DCP analysis gave a Dw of 140 nm. This is in very good agreement with the above estimate of 139 nm and is also consistent with our electron microscopy and BET data. A proton NMR spectrum of the dissolved latex was recorded in CD2Cl2 (see Figure 2). The four equivalent aliphatic ethylene glycol protons are clearly visible at δ 3.7. This peak integral can be compared with the aromatic peak integral due to the styrene residues at δ 6.3-7.3. Thus the molar ratio of ethylene oxide (EO) to styrene units can be calculated, which corresponds to a mass content of ca. 15%. By this method the surface absorbed amount, Γ, of the PEG stabilizer was determined to be 2.2 mg m-2. Here it is assumed that all of the PEG stabilizer is located at the surface of the PS particles. This is highly likely given the postgrafting method used to attach the stabilizer.15 (17) Cosgrove, T. G.; Ryan, K. Langmuir 1990, 6, 136.
Polypyrrole-Polystyrene Composite Particles
Langmuir, Vol. 15, No. 23, 1999 8055
Figure 2. Proton NMR spectrum of the PS-PEG latex dissolved in CD2Cl2. The PEG stabilizer content of this latex was calculated to be approximately 15.1% by mass.
SEM studies confirmed that the PS particles were spherical and near-monodisperse. Thus it is possible to determine the PPy mass loading required to achieve a theoretical mean overlayer thickness using eq 2, which assumes that the PPy is deposited as a smooth, continuous PPy overlayer which encapsulates the PS latex.
x)R
((
M2F1 +1 M1F2
) ) 1/3
-1
(2)
R is the radius of the uncoated latex particles, M1 and F1 are the mass fraction and density of the PS component, and M2 and F2 are the mass fraction and density of the PPy component, respectively. The bulk densities of PS and PPy were determined to be 1.05 and 1.46 g cm-3 by helium pycnometry. The concentrations of pyrrole monomer and FeCl3 oxidant were kept constant for all PPy deposition experiments except PS-PEG-PPyLSA. The PPy loading was controlled by varying the initial concentration of PS latex particles and hence the available surface area (see Table 1). In the case of PS-PEG-PPyLSA, the initial pyrrole concentration was greatly reduced in order to decrease the total latex surface area required for a given loading. This experiment was carried out in order to compare the deposition of PPy onto submicrometer-sized PS particles at the same relatively low latex surface area employed for the analogous micrometer-sized PS latex.11 For example, a PS latex of 1.6 µm diameter was used at a concentration which corresponded to a total latex surface area of 7.1 m2. Under these conditions a 4.6 wt % PPy loading was achieved. This value is comparable to that of PS-PEGPPyLSA (see Table 1). A high magnification transmission electron micrograph of the PS-PEG-PPy(4.2) composite is shown in Figure 3. Discrete PPy nanoparticles of 20-30 nm are visible, and a large proportion of the latex surface appears to be bare. Clearly there is no evidence for the expected “coreshell” morphology. This is in direct contrast to the work of Lascelles and co-workers, who demonstrated that the equivalent micrometer-sized PS latex was coated with smooth, uniform PPy overlayers by solvent extraction of the soluble PS core and examination of the remaining PPy residues by SEM.12 Figure 4 shows a scanning electron micrograph of the PS-PEG-PPy(4.2) composite particles dried down from
dilute aqueous solution. It is clear that incipient flocculation of the PS latex occurs during PPy deposition: the majority of the particles are present as colloidal microaggregates rather than singlets. This is in good agreement with the reduced degree of dispersion and broad particle size distribution indicated by DCP studies (see later). Figure 5 shows a plot of conductivity against PPy loading for a series of PS-PPy composites. Conductivities for these composites are compared to those reported by Lascelles and Armes,11 who prepared a series of micrometer-sized PPy-coated PS latexes. For a given PPy loading, the conductivities of the submicrometer-sized composites are significantly lower than those of the micrometer-sized “core-shell” particles. Since TEM studies suggested that the composite particles did not possess the expected “coreshell” morphology (see Figure 3) macroscopic charge transport through the material is relatively inefficient due to the electrically insulating PS-PEG latex component. Thus the composite particles exhibit a classical percolation conductivity curve which is similar to that of a heterogeneous admixture of dried PS latex and PPy bulk powder.11 Previous FTIR spectroscopy studies of micrometer-sized PPy-coated PS latexes were interpreted as providing some evidence of the “core-shell” morphology of these composites.11 It was suggested that the “core-shell” morphology and the diameter (similar to the wavelength of IR radiation) of these particles led to enhanced IR absorption of the conducting polymer component. Similar effects have been observed in Raman spectroscopy studies.12 FTIR spectra of the dried PS-PEG latex and PS-PEG-PPy(28.1) composite are shown in Figure 6a and Figure 6c, respectively. The spectrum for the uncoated PS latex is typical for that of PS, with an additional strong band ca. 1100 cm-1 attributable to the C-O stretch of the PEG component. The PS-PEG-PPy(28.1) composite latex contains several additional strong bands at 1549, 1316, 1186, and 910 cm-1 due to the doped PPy component.18-20 As a control experiment, an IR spectrum of a heterogeneous admixture comprising 72% uncoated latex and 28% PPy bulk powder was recorded, but the PPy bands were not visible (see Figure 6b). It is now known from TEM studies of the PS-PEG-PPy(X) series (Figure 3) that these composites do not possess a “core-shell” morphology, thus the enhancement of the PPy bands in the spectrum of the PS-PEG-PPy(28.1) latex must occur for some other reason. It is likely that the PPy component is poorly dispersed in the heterogeneous admixture due to inefficient grinding. As a result, the PS bands would not be attenuated by the PPy component to the same extent as in the composite latexes, in which the PPy component is well-dispersed at the nanoscale. Thus, a high degree of dispersion (rather than a “core-shell” morphology) appears to be a prerequisite for effective attenuation of the PS bands in the FTIR spectrum. In summary, FTIR spectroscopy is not a suitable technique for assessing the uniformity of the conducting polymer overlayers on these PPy-coated PS latexes. Previous studies have shown DCP to be a useful technique with which to determine the colloidal stability of the micrometer-sized PPy-coated PS latexes.11 Visual inspection of the PS-PEG-PPy(X) series suggested that, (18) Satgurunathan, R.; Ottewill, R. H. Colloid Polym. Sci. 1995, 273, 379. (19) See, for example, the Proceedings of the 1992 International Conference on Synthetic Metals (ICSM ’92) Synth. Met. 1993, 55-57. (20) Bjorklund, R. B.; Liedberg, B. J. Chem. Soc., Chem. Commun. 1986, 16, 1293.
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Figure 3. Transmission electron micrograph of PS-PEG-PPy(4.2) (experiment no. 10 in Table 1).
at low PPy loadings (
