Preparation of Three-Dimensional Polymeric Structures Using Gas

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Preparation of Three-Dimensional Polymeric Structures Using Gas Bubbles as Templates Maciej Mazur Department of Chemistry, UniVersity of Warsaw, Pasteura 1, 02-093 Warsaw, Poland ReceiVed: January 28, 2008; ReVised Manuscript ReceiVed: June 22, 2008

Three-dimensional polymeric structures supported on glass slides were synthesized by spatially selective polymerization of 2-methoxyaniline or 2-ethoxyaniline onto micrometer-sized gas bubbles. The gas bubbles play the role of templates that direct the polymer growth in the form of spherical capsules. It was shown that the polymerization reaction is initiated at the gas/solution interface and is followed by growth extending onto the glass/solution interface. In consequence, two pathways of capsule formation can be distinguished. The first pathway involves the adsorption of gaseous bubbles onto glass, which is followed by coating the adsorbed bubbles with the polymer. This yields a relatively small number of polymeric capsules decorating the surface. In the second pathway, the gas bubbles generated in the bulk of the solution are first coated with the polymer and then adsorbed onto the glass surface (already modified with a thin polymeric film). In this process, a large number of polymeric particles accumulate on the surface. The growth of polymeric capsules was examined using several experimental techniques, including scanning electron microscopy, near-field scanning optical microscopy, UV-vis spectroscopy, and conductivity measurements. Introduction Nano- and microstructures have gained considerable attention in recent years due to their remarkable optical, mechanical, catalytic, and electrical properties.1,2 These include both naturally occurring materials, e.g., skeletons of living organisms that exhibit nanogranular organization3,4 as well as materials that are synthetically produced on a laboratory or industrial scale.5-7 Among others, conducting polymers are of special interest as they display unusual electronic properties such as high electron affinities, low-energy optical transitions, and low ionization potentials. Their interesting features make them suitable for use in organic semiconductors, sensors, electromagnetic shields, anticorrosive and antistatic coatings, secondary batteries, and electrochromic devices.8-12 Nano- and microstructures of conducting polymers are prepared by several methods. One of the most spectacular examples is the hard template approach, first introduced by Martin et al.13-15 This involves the application of a well-defined “hard” template, e.g., membrane containing nanometer-sized cylindrical pores, which directs the deposition of a conducting polymer in the form of nanostructures, e.g., nanotubes or nanowires. Since then, several other morphologies fabricated with other templates have been reported, including honeycomb structures,16 inverted opals, 17-19 or hollow particles.20-23 In the so-called “soft” template method, the application of “soft” assemblies such as surfactant micelles, liquid crystals, or polymers is used to prepare nanotubes,24 nanowires,25 hollow microspheres,26-28 or “microleaves”.29 It was recently shown that gaseous microbubbles generated in the solution can be successfully used as soft templates to fabricate polymeric hollow microstructures. Shi et al. used gaseous bubbles generated at the counter electrode to electrochemically fabricate polypyrrole microstructures such as bowls, bottles, and so forth.30-32 Bajpai et al. applied electrochemically generated hydrogen bubbles to template polypyrrole deposition in the form of hollow polymeric microspheres.33 These microspheres were subsequently used to encapsulate fluorescent molecules. Oxygen bubbles generated through the decomposition of hydrogen peroxide were used to

prepare poly(2-methoxyaniline) (POMA) microrings adjacent to the glass substrate.34 Electrochemically produced hydrogen microbubbles were also applied to template formation of microholes within polymeric films deposited on a metallic surface. Such hole-containing structures were subsequently used to fabricate silver microislands decorating the electrode surface.35 In this paper, gaseous microbubbles generated in the solution through gradual decomposition of potassium pyrosulfate are used to prepare three-dimensional spherical capsules supported on a glass substrate. The key idea of this approach is to chemically polymerize 2-alkoxyanilines, which are known to exhibit anomalous polymerization behavior.36 It has been shown that in the initial stages of 2-alkoxyanilines oxidation, only soluble oligomeric species are formed, and no polymerization reaction is observed in the bulk of the solution.37,38 Instead, the polymer may be formed at phase boundaries, e.g., at the metal/solution39 or solution/air interface.34 The oligomeric species generated in the bulk of the solution, being in nonreactive quinoid form, are accumulated at the interface where they are transformed into the more reactive semiquinoid form.40,41 As a result, the polymerization is promoted at the interface, while it is hindered in the bulk of the solution. In contrast, some other aniline derivatives, e.g. 2-methylaniline,34,41 2,5-dimethoxyaniline,37 and aniline itself,40,42-44 do not exhibit such polymerization behavior. Since nonreactive oligomeric species are not generated, the polymerization of these compounds proceeds in the entire volume of the reaction mixture, and no preferential polymer growth at phase boundaries is observed. The preferential polymerization of 2-methoxyaniline and 2-ethoxyaniline at the gas/solution interface is used in this work to deposit polymers directly onto the surface of gas bubbles. The gas microbubbles act as a kind of a template that directs the polymer growth, which results in the formation of threedimensional spherical polymeric structures.

10.1021/jp8008089 CCC: $40.75  2008 American Chemical Society Published on Web 08/08/2008

Gas Bubble Templates for 3D Polymeric Structures

Figure 1. SEM images of three-dimensional POMA microcapsules prepared using “aged” ammonium persulfate: (a) hollow microcapsule, (b) broken microcapsule.

Figure 2. Size distribution of gaseous bubbles in 20 mM potassium pyrosulfate solution.

Materials and Methods Chemicals. All chemicals were of the highest quality commercially available: 2- methoxyaniline (Aldrich, 99%), 2-ethoxyaniline (Aldrich, >97%), ammonium persulfate (Fluka, >98%), ammonium persulfate “aged” (Fluka, >98%, stored at room temperature for ca. 10 years), potassium pyrosulfate (J.T.

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Figure 3. (a) Dependence of absorbance at 750 nm versus time for aqueous 1 M HCl solution containing monomer (0.18 M), ammonium persulfate (0.44 M), and potassium pyrosulfate (20 mM): (i) 2-methoxyaniline, (ii) 2-ethoxyaniline. (b) FTIR spectra of polymeric capsules in KBr pellets: (i) POMA (polymerization time 9 min), (ii) POEA (polymerization time 20 min).

Baker), and sulfuric acid (POCh, reagent grade). Aqueous solutions were prepared from water of high purity (Milli-Q Plus). Instrumentation. Scanning electron microscopy (SEM) images were obtained with a LEO 435 VP microscope. Gas bubble size distribution was determined with a laser diffraction technique using a particle size analyzer (Mastersizer 2000, Malvern Instruments). UV-vis measurements were performed with a Lambda 25 (Perkin-Elmer) spectrometer. IR spectra of polymeric capsules in KBr pellets were measured with a Shimadzu 8400 Fourier transform infrared (FTIR) spectrometer (Kyoto, Japan). The sheet resistance of polymeric ad-layers was determined using a four-probe technique (Jandel RM3, Jandel Engineering). Atomic force microscopy (AFM; Nanoscope IIIa, Digital Instruments, Veeco) operating in contact mode was used to determine the thickness of polymeric deposits. Near-field scanning optical microscopy (NSOM; MultiView 4000, Nanonics) working in transmission mode was used to record the NSOM images. The light source for NSOM was a He-Cd laser (Kimmon Koha Co.) operating at 442 nm. The transmitted light was collected in far field with an

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Figure 4. Low magnification SEM images of polymeric microcapsules deposited on a glass surface: (a) POMA, polymerization time 9 min; (b) POEA, polymerization time 20 min.

inverted optical microscope (Olympus) equipped with a PMT detector (Perkin-Elmer). Procedures and Materials Glass Substrates. For the deposition of polymeric capsules, conventional microscopic coverslips were used. For SEM measurements, the substrates (with polymeric deposits) were sputter coated with a thin palladium-gold adlayer. Preparation of Polymeric Capsules Supported on Glass. For the preparation of polymeric capsules, the glass substrates were placed in a polymerization bath that was prepared by the addition of 2 cm3 of 0.36 M monomer (2-methoxyaniline or 2-ethoxyaniline) in aqueous 1 M HCl to the same volume of the solution containing ammonium persulfate (0.88 M) and potassium pyrosulfate (40 mM) in 1 M aqueous HCl. The glass substrates were left in the polymerization bath for a specified period of time (typically 9 min for POMA and 20 min for poly(2-ethoxyaniline) (POEA)), after which they were removed and placed in aqueous 1 M HCl for a couple of seconds to eliminate unbound polymeric material. The glass substrates were then removed from the aqueous acid, and finally dried under a stream of air. The polymeric capsules synthesized using “aged” ammonium persulfate were fabricated by immersion of the glass substrates into a solution prepared by mixing 2 cm3 of 0.36 M 2-methoxyaniline in 1 M HCl with the same volume of 0.4 M “aged”

Figure 5. POEA capsules deposited on glass at different polymerization times: (a) 10 min, (b) 15 min, (c) 20 min.

ammonium persulfate in 1 M HCl. The samples were removed from the polymerization solution after 20 min, then rinsed with water and dried. Preparation of Polymeric Capsules in the Bulk of the Solution. The “unsupported” polymeric capsules were prepared by essentially the same method. The monomer solution (2 cm3 of 0.36 M 2-methoxyaniline or 2-ethoxyaniline in aqueous 1 M HCl) was added to the same volume of ammonium persulfate (0.88 M) and potassium pyrosulfate (40 mM) in 1 M aqueous HCl. The solution was left for 9 or 20 min (for 2-methoxyaniline and 2-ethoxyaniline, respec-

Gas Bubble Templates for 3D Polymeric Structures

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Figure 6. Size distribution histograms of polymeric capsules deposited on a glass surface at different polymerization times: (a) POMA, 5 min; (b) POMA, 7 min; (c) POMA, 9 min; (d) POEA, 10 min; (e) POEA, 15 min; (e) POEA, 20 min.

Figure 7. Polymeric microcapsules formed in the bulk of the polymerization solution: (a) SEM image of POMA capsules, (b) SEM image of POEA capsules, (c) size distribution of POMA capsules, and (d) size distribution of POEA capsules.

tively) to allow for capsule growth. Then, 200 µL of the suspension was added to 1 cm3 of distilled water and centrifuged at 13000 rpm for 30 s. After decantation, the procedure was repeated several times until the solution became colorless. A drop of the solution containing polymeric particles was subsequently added onto a glass slide and allowed to dry. The samples were then sputter-coated with Pd-Au and examined using SEM.

Results and Discussion The idea of using gas bubbles to template the growth of threedimensional polymeric capsules comes from a simple observation that when aged ammonium persulfate (oxidant) is used to polymerize 2-methoxyaniline, several micrometer-sized hollow structures are formed on the walls of the glass reaction vessel. Examples of such objects are presented in Figure 1. The aging process of ammonium persulfate most likely involves its

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Figure 8. NSOM of a polymeric ring left after detachment of the capsule (POEA, 15 min): (a) topography mode image, (b) transmission mode image, (c) cross section profile through the topography image, and (d) cross section profile through the transmission image.

transformation to pyrosulfate, which further gradually decomposes in aqueous solution with the evolution of gaseous products,45 according to the equation

S2O72- + H2O f H+ + SO42- + HSO3- + 1/2O2 As a consequence, when aged ammonium persulfate is used as an oxidant in 2-methoxyaniline polymerization reaction, large amounts of gaseous microbubbles are produced in the bulk of the solution as well as on the walls of the reaction vessel. Simultaneously, the oxidation of the monomer effects in deposition of the polymer at the bubbles’ gas/solution interface, yielding polymeric capsules. As seen from Figure 1, the polymeric structures contain an empty hollow inside. Since the generation of polymeric capsules using aged ammonium persulfate is obviously not a well-controlled process, potassium pyrosulfate was deliberately added to the reaction mixture to produce gaseous bubbles to mimic the effect of aged persulfate in a controlled manner. The size distribution of gaseous bubbles formed in the solution of K2SO7 was studied with a laser diffraction technique. The distribution curve is shown in Figure 2. The typical size of the gaseous bubbles is in the range of several micrometers and does not change significantly with time (within several tens of minutes). The gaseous bubbles produced in this manner were further used to template the growth of conducting polymers in the form of spherical capsules. Two derivatives, methoxy- and ethoxya-

niline, were used in the polymerization reaction. It should be mentioned that the polymerization was carried out in an acidic solution, and no monomer droplets were present that would act as templates for polymer growth.46,47 Shown in Figure 3a is the dependence of absorbance at 750 nm for 2-methoxayniline and 2-ethoxyaniline being oxidized in the solution containing persulfate (oxidant) and pyrosulfate (gas initiator). The absorbance in this range is indicative of polymer formation in the reaction mixture.36 One can see that oxidation and further coupling reactions are significantly faster for 2-methoxyaniline when compared to the ethoxy derivative (a result that is in accordance with previous literature reports36). For this reason, different polymerization times were used in the preparation of polymeric capsules of POMA and POEA that correspond to the same value of absorbance (9 min for POMA and 20 min for POEA). Polymeric capsules supported on the glass surface were prepared by placing glass slides in the solution containing monomer, oxidant, and pyrosulfate. The slides were subsequently removed, gently rinsed with HCl, and dried. The structure of the deposits was studied further with infrared spectroscopy. The FTIR spectra of POMA and POEA deposits recorded in KBr pellets are depicted in Figure 3b. They reveal typical patterns known for POMA41 and POEA.48 Specifically, one can distinguish characteristic vibration bands attributable to polyanilines. The absorption band related to the CdN quinoid ring vibration appears at 1556 cm-1 (POMA) and 1558 cm-1

Gas Bubble Templates for 3D Polymeric Structures (POEA). The CdC benzenoid-type ring vibration is observed at 1490 cm-1 (POMA) and 1505 cm-1 (POEA). The 1445 cm-1 (POMA) and 1453 cm-1 (POEA) bands seen in the spectra are attributable to the CdC quinoid ring stretching vibration. The deposits were subsequently studied with a scanning electron microscope (SEM). Shown in Figure 4are SEM images of POMA and POEA deposits, respectively. In both cases, spherical polymeric capsules scattered on the surface were produced. The capsules are assembled on a thin layer of polymeric material that coats the glass surface. The thickness of the underlying film for both polymers is ca. 500 nm, as determined on the basis of AFM data (not shown). The polymeric films are mechanically continuous, which is confirmed by sheet resistance measurements using a four-probe method. The value recorded for POMA is 0.501 MΩ/square, while for POEA it is 18.2 MΩ/square. Assuming a film thickness of 500 nm, one recovers a bulk conductivity of 4.0 × 10-2 Ω-1cm-1 and 1.1 × 10-3 Ω-1cm-1 for POMA and POEA, respectively. These values are in good agreement with conductivities reported in the literature.49,50 On the contrary, for shorter polymerization times, the sheet resistances are above the limit of our instrument capabilities. This is likely due to discontinuity of the polymeric films deposited on the surface. To verify this possibility, several SEM images were recorded for different polymerization times. Shown in Figure 5 are POEA deposits produced after 10, 15, and 20 min, respectively. One can see that, initially, the microcapsules are directly “attached” to the surface of glass, and no underlying polymeric film is formed (Figure 5a). For longer polymerization times circular rings under the capsule are radially grown, but they still do not overlap and do not form a continuous film (Figure 5b). Finally, the whole glass surface is coated with a polymer with several capsules projecting from the layer (Figure 5c). Qualitatively, similar results are also observed for POMA. The capsules produced on the surface are empty inside, as shown by the SEM images of the broken structures (Supporting Information). The surface loading density of capsules and their size significantly depends on polymerization time. For both polymers, initially the amount of the structures remains at a relatively low level of 3.65 × 103 and 7.07 × 103 capsules/cm2 for POMA (polymerization time 5 min) and POEA (polymerization time 10 min), respectively. With increasing reaction time, these numbers rise to 1.06 × 104 (POMA, 7 min) and 1.58 × 104 capsules/cm2 (POEA, 15 min), finally reaching values as high as 4.52 × 104 (POMA, 9 min) and 2.43 × 105 capsules/cm2 (POEA, 20 min). The size distribution histograms derived from SEM images recorded for different polymerization times are presented in Figure 6. For both polymers, one can see the apparent trend is a slight decrease in the mean capsule diameter with polymerization time. For POMA the average capsule diameter decreases from 8.9 µm (5 min) through 6.8 µm (7 min) to 5.4 µm (9 min). For POEA these numbers are as follows: 8.2 µm (10 min), 8.4 µm (15 min), and 5.0 µm (20 min). At this point, the question that inevitably arises is whether the polymeric capsules are formed on the glass surface only or if they are also created in the bulk of the polymerization solution. To answer this question, the polymeric product yielded in the bulk of the solution was separated by centrifugation, casted onto glass slides, and imaged with SEM. Shown in Figure 7a,b are microscopic images of POMA and POEA deposits, respectively. It is apparent that in both cases round capsules were produced. Their diameter distribution (Figure 7c,d) well match the size of capsules supported on the surface (Figure 6).

J. Phys. Chem. C, Vol. 112, No. 35, 2008 13533 On the basis of the above observations, one can propose a general scheme of polymeric capsule formation. Because of the decomposition of potassium pyrosulfate, gaseous bubbles are generated in the solution, some of which are adsorbed onto the surface of the glass substrate. Since the oxidant and monomer are both present in the reaction mixture, the polymerization takes place preferentially at the bubbles’ gas/solution interface. In consequence, both surface-supported and nonadsorbed bubbles become coated with a thin layer of polymer. After formation of the capsules, further polymer growth occurs. Two-dimensional rings grow radially, starting from the spots where the capsules are attached to the glass substrate. The diameter of the rings typically does not exceed 50 µm. Further increase of the reaction time results in polymer deposition in the form of a thin film on the entire surface of the glass substrate. This changes the adsorption properties of the substrate considerably, resulting in the accumulation of already-formed polymeric particles from the bulk of the solution. It is important to note that polymeric capsules formed at short polymerization times are statistically slightly larger than those yielded at longer times. The reason for this seems to be associated with the different adsorption rate of gas bubbles depending on their size. On the basis of Hertz theory,51 which predicts that the force applied to the adsorbing particle yielding a given contact area is inversely proportional to the radius of the particle, one can conclude that the larger the gaseous bubble, the easier its adsorption onto the glass surface. As a result, from the entire population of gas bubbles generated in the bulk of the solution, those with larger diameter are more favorably adsorbed. Therefore, initially, only larger capsules are deposited onto the surface. When the entire glass substrate is coated with a thin polymeric film, the adhesion properties of the surface are diametrically changed, and the adsorption of capsules occurs regardless of their size. In consequence, the statistical contribution from the smaller capsules is more significant, and this yields a smaller mean diameter of the particles measured. In order to further strengthen the conclusion that at initial stages of the process the capsules are grown onto the bubbles that are directly adsorbed on the glass surface, and not accumulated after formation in the bulk of the solution, NSOM was used. The POEA capsules (15 min polymerization) were mechanically removed from the surface by extensive rinsing of the sample with water. The ring structures left on the surface (compare Figure 5b) were then imaged with NSOM. Shown in Figure 8 are simultaneous NSOM images recorded in topography and transmission modes. The topography reveals that the ring looks like a volcano, with gradually increasing slopes and a deep hole at the center of the structure. The depth of the hole, as read from the cross section profile (Figure 8c), is at least 350 nm. In transmission mode, the intensity of the light passed through the sample is measured. With an increase of the polymer thickness the intensity decreases, which is seen as a dark color on the image. When the tip images the hole, the spot on the image is bright as the light effectively transmits through the sample. The corresponding cross section profile is shown in Figure 8d. The above results confirm that the capsule was deposited directly onto the substrate. One may also conclude that the empty interior of the capsule extends as far as the glass surface. If the capsule was adsorbed onto the already grown polymeric film or ring, the removal of the capsule would likely not result in the formation of the hole. Conclusions It has been shown that gaseous microbubbles can be effectively used to template the growth of three-dimensional

13534 J. Phys. Chem. C, Vol. 112, No. 35, 2008 polymeric structures both on the surface of glass and in the bulk of the solution. Poly(2-alkoxyanilines) are preferentially deposited at the gas/solution interface, therefore the polymerization proceeds on the surface of gas bubbles generated in the solution resulting in the formation of three-dimensional structures. The deposition of capsules onto the surface may proceed through two pathways. In the first pathway, the gas bubbles are adsorbed onto the glass surface and the polymer is deposited onto the bubble. In the second pathway, the capsules are formed through the coating of bubbles in the bulk of the solution, and then adsorbed onto the surface. Acknowledgment. The funding for this work was provided by the Ministry of Science and Higher Education within Project N204 117 32/3116 for years 2007-2010. Particle size analysis and NSOM measurements were conducteded in the Structural Research Laboratory (SRL) at the Department of Chemistry, University of Warsaw, Poland. SRL has been established with financial support of the European Regional Development Fund in the Sectoral Operational Program “Improvement of the Competitiveness of Enterprises, years 2004-2006” Project No. WKP_1/1.4.3./1/2004/72/72/165/2005/U. Supporting Information Available: SEM images of broken POEA capsules. This information is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bre´das, J. J.; Lo¨gdlund, M.; Salaneck, W. R. Nature 1999, 397, 121. (2) Bracht, H.; Nichols, S. P.; Walukiewicz, W.; Silveira, J. P.; Briones, F.; Haller, E. E. Nature 2000, 408, 67. (3) Przeniosło, R.; Stolarski, J.; Mazur, M.; Brunelli, M. J. Struct. Biol. 2008, 161, 74. (4) Stolarski, J.; Meibom, A.; Przeniosło, R.; Mazur, M. Science 2007, 318, 92. (5) Tang, C. W. Appl. Phys. Lett. 1986, 48, 183. (6) Wirtz, M.; Martin, C. R. AdV. Mater. 2003, 15, 455. (7) Oaki, Y.; Imai, H. AdV. Funct. Mater. 2005, 15, 1407. (8) Novak, P.; Muller, K.; Santhanam, K. S. V.; Haas, O. Chem. ReV. 1997, 97, 207. (9) Dhawan, S. K.; Singh, N.; Venkatachalam, S. Synth. Met. 2001, 125, 389. (10) Somani, P.; Mandale, A. B.; Radhakrishnan, S. Acta Mater. 2000, 48, 2859. (11) Conroy, K. G.; Breslin, C. B. Electrochim. Acta 2003, 48, 721.

Mazur (12) Maziarz, E. P.; Lorenz, S. A.; White, T. P.; Wood, T. D. J. Am. Soc. Mass Spectrom. 2000, 11, 659. (13) Martin, C. R.; Van Dyke, L. S.; Cai, Z.; Liang, W. J. Am. Chem. Soc. 1990, 112, 8976. (14) Martin, C. R. Acc. Chem. Res. 1995, 28, 61. (15) Martin, C. R. Science 1994, 266, 1961. (16) Han, S.; Briseno, A. L.; Shi, X.; Mah, D. A.; Zhou, F. J. Phys. Chem. B 2002, 106, 6465. (17) Cassagneau, T.; Caruso, F. AdV. Mater. 2002, 14, 34. (18) Cassagneau, T.; Caruso, F. AdV. Mater. 2002, 14, 1629. (19) Yu, A.; Meiser, F.; Cassagneau, T.; Caruso, F. Nano Lett. 2004, 4, 177. (20) Jiang, P.; Bertone, J. F.; Colvin, V. L. Science 2001, 291, 453. (21) Hao, L.; Zhu, C.; Chen, C.; Kang, P.; Hu, Y.; Fan, W.; Chen, Z. Synth. Met. 2003, 139, 391. (22) Feng, X.; Mao, C.; Yang, G.; Hou, W.; Zhu, J.-J. Langmuir 2006, 22, 4384. (23) Marinakos, S. M.; Novak, J. P.; Brousseau, L. C.; House, A. B.; Edeki, E. M.; Feldhaus, J. C.; Feldheim, D. L. J. Am. Chem. Soc. 1999, 121, 8518. (24) Dai, T. Y.; Lu, Y. Macromol. Rapid Commun. 2007, 28, 629. (25) Zhang, L. J.; Wan, M. X. Thin Solid Films 2005, 477, 24. (26) Zhu, Y.; Hu, D.; Wan, M. X.; Jiang, L.; Wei, Y. AdV. Mater. 2007, 19, 2092. (27) Zhang, L; Wan, M AdV. Funct. Mater. 2003, 13, 815. (28) Cheng, D; Xia, H.; Chan, H. S. O. Langmuir 2004, 20, 9909. (29) Han, J.; Song, G. P.; Guo, R. AdV. Mater. 2007, 19, 2993. (30) Qu, L; Shi, G. Chem. Commun. 2003, 206. (31) Ma, M.; Qu, L.; Shi, G. J. Appl. Polym. Sci. 2005, 98, 2550. (32) Yuan, J.; Qu, L.; Zhang, D.; Shi, G. Chem. Commun. 2004, 994. (33) Bajpai, V.; He, P.; Dai, L. AdV. Funct. Mater. 2004, 14, 145. (34) Mazur, M.; Frydrychewicz, A. J. Appl. Polym. Sci. 2007, 106, 2169. (35) Mazur, M.; Michota-Kamin´ska, A.; Bukowska, J. Electrochem. Commun. 2007, 9, 2418. (36) Mazur, M.; Blanchard, G. J. Langmuir 2004, 20, 3471. (37) Mazur, M.; Krysinski, P. Electrochim. Acta 2001, 46, 3963. (38) Mazur, M.; Krysinski, P. Langmuir 2001, 17, 7093. (39) Mazur, M.; Predeep, P. Polymer 2005, 46, 1724. (40) Mazur, M.; Michota-Kamin´ska, A.; Bukowska, J. Electrochim. Acta 2007, 52, 5669. (41) Mazur, M. Eur. Phys. J. E 2007, 22, 67. (42) Sapurina, I.; Fedorova, S.; Stejskal, J. Langmuir 2003, 19, 7413. (43) Stejskal, J.; Trchova, M.; Fedorova, S.; Sapurina, I.; Zemek, J. Langmuir 2003, 19, 3013. (44) Malinauskas, A. Polymer 2001, 42, 3957. (45) Cleaver, K. D.; Davies, J. E. D. J. Raman Spectrosc. 1980, 9, 376. (46) Wei, Z.; Wan, M. AdV. Mater. 2002, 14, 1314. (47) Han, J.; Song, G.; Guo, R. Chem. Mater. 2007, 19, 973. (48) Yeh, J. M.; Chen, C. L.; Chen, Y. C.; Ma, C. Y.; Lee, K. R.; Wei, Y.; Li, S. X. Polymer 2002, 43, 2729. (49) Gazotti, W. A.; DePaoli, M. A. Synth. Met. 1996, 80, 263. (50) Liao, Y. H.; Angelopoulos, M.; Levon, K. J. Polym. Sci., Part A 1995, 33, 2725. (51) Butt, H. J.; Graf, K.; Kappl, M. Physics and Chemistry of Interfaces; Wiley-VCH GmbH & Co. KGaA: Weinheim, Germany, pp 111-112.

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