자기 응집된 막을 이용한 TS-1 나노 입자에 폴리피롤 초박막

증착에 관한 연구

조 규진*, 박 권필*, 문 일식*, 설 용건**, 정 경택**, 이 재석***

*국립 순천 대학교, 화학공학과, 전남 순천, 540-742

**연세 대학교, 화학공학과, 서울, 120-749

***광주 과학기술원(K-JIST), 물질과학공학과, 광주

Nanothickness Polypyrrole Films Deposition on TS-1

Nanoparticles Using Self-assembled Bilayers

Gyoujin Cho*, Kwonphil Park*, Il-Shik Moon*, Dyeong Tack Jung**,

and Jae-Suk Lee***

*Department of Chemical Engineering, Sunchon National University,

Sunchon, Chun Nam 540-742, Korea

**Department of Chemical Engineering, Yonsei University, 120-749 Seoul, Korea

***Department of Material Science and Engineering, Kwangju Institute of Science and Technology (K-JIST), Kwangju, Korea

Introduction

The use of surfactants adsorbed onto metal oxide surfaces as a medium for the formation of ultra-thin polymer films has been reported in recent years using a three-step process called the thin film via surfactant template (TFST) technique [Glatzhofer et al., 1993]. The TFST method has potential for the formation of anti corrosion and lubricating coatings, and composite materials formed using this technique may be valuable for use as pigments, reinforcing fillers, and chromatographic packings.

Such studies have focused almost exclusively on macroparticles or plates for the convenience in characterization and understanding in the ultra-thin polymer films growing mechanism. However, microheterogeneous (colloidal) systems of conducting polymers (e.g. PPY and polyaniline), capable of fabricating into desirable solid objects such as parts, films, fibers, coatings, etc., will be extremely beneficial to improve the processability of these otherwise intractable materials.

The first synthesis of colloid PPY particles using methylcellulose as a stabilizer in aqueous phase was reported by Bjorklund and Liedberg in 1986. Subsequently, various research groups have shown that a variety of both commercial, and tailor0made water soluble polymers can be used as steric stabilizer for PPY. In addition, in a series of recent papers the Sussex group has reported the preparation and characterization of both polyaniline(PYA)-metal oxide and PPY-metal oxide nanocomposites using ca. 20nm silica particles as dispersants in aqueous media[Flitton et al., 1995]. Although those dispersions generally exhibit good long-term colloid stability, as far as we are aware, there have been no publications regarding for obtaining the desired microscopic and macroscopicstructural homogeneity using the microheterogeneous systems.

We have previously reported that using the TFST method on metal oxides could dramatically alter the intrinsic surface properties of substrates so that the properties of deposited PPY films were significantly influenced by both aggregated structure and molecular orientation of physisorbed surfactants on metal oxide surface [Nishizawa et al., 1991]. In addition, the physisorbed surfactants also play an important role in both the nucleation and growth of polymer films.

In the present work we report the first PPY ultra-thin film deposition study on nano-sized particles surface using the TFST method in which a surfactant (CPC) can be adsorbed and formed bilayer on the surface of a charged TS-1 nanoparticle suspended in an aqueous system. Since TS-1 nanoparticles have completely different surface properties from the amorphous metal oxides, the resulting novel properties of PPY ultra-thin films can be expected [Wu and Bein, 1994]. Those resulting ultra-thin PPY films homogeneously coated TS-1 nanocomposites have been extensively characterized in terms of their particle size, chemical composition, dc electrical conductivity, and surface composition using scanning electron microscopy (SEM), dynamic light scattering, and solid state Si29-NMR.

Experimental

Materials. Ceptylpyridinium Chloride (CPC) was purchased from Aldrich, and recrystallized in acetone before using. Pyrrole (98%, Aldrich) was purified by passing it through a short column of basic alumina, activity grade Ⅰ (Sigma). High surface area (550m2/g) TS-1 nanosized particles prepared following previously reported method25. Reagent grade ammonium persulfate (Mallinckrodt) was used without further purification. Double distilled and deionized water was used in the all systems.

PPY Deposition. For polymerization of pyrrole on TS-1 particles, an optimal condition (at pH6 with an 1mM of CPC for bilayer formation) was chosen from the adsorption study of CPC on TS-1 particles. Polymerizations of pyrrole on adsorbed CPC bilayers were initiated by adding an equimolar amount of FeCl3 (based on the pyrrole) into the reaction mixtures. In this work, we used 5□ of 0.02wt% TS-1 dispersed solutions.

Results and Discussion

The Sussex group has reported [Fliton et al., 1995] that the small silica particles act as a high surface area colloidal substrate for the precipitating polyaniline or PPY and resulting composite particles consist of micro-aggregates of silica particles "glued" together by the conducting polymer component. Those conducting polymer-silica syntheses can produce stable colloidal dispersions of raspberry-shaped particles in the 100-300nm size range if the reaction carried out under very dilute concentration. Those resulting PPY/silica composited have heterogeneous surface morphology. In other words, silica surface can not be coated homogeneously by PPY using their method. However, by adapting the self-assembled CPC bilayers (SCB) on TS-1 nanoparticles, we did prepare the PPY homogeneously coated (nm thickness) TS-1 particles which are stable colloidal dispersions depending on the pyrrole loading ratio to the TS-1 and CPC.

A dispersion of base TS-1 particles(T1), PPY coated TS-1 particles(T2) using the SCB, and PPY coated TS-1(T3) without the SCB were examined respectively by SEM, dynamic light scattering, solid state Si29-NMR and contact conductivities.

From the results of SEM and the dynamic light scattering, T1 showed about 100nm particle size. In addition, T2 showed about 120nm particle size (Fig.1). Both T1 and T2 were not aggregated at all and showed spherical mono dispersed particles. However, T3 was largely aggregated particles which were consistent with the previous reports of the Sussex group. Also, from the solid state Si29-NMR, T2 dose not show any Si peak while both T1 and T3 show Si peak. The contact conductivity of T2 was higher than that of T3. Those results indirectly suggest that T2 is homogeneously coated by ultrathin PPY films. The speculated thickness of deposited PPY film is about 20nm based on the results of SEM and dynamic light scattering.

Acknowledgement : This work is partially supported by Korea Research Research Foundation [04-E-0060], 1996.

References

Flitton, R., Johal, J., Maeda, So, and Armes, S. P., "Synthesis of Colloidal Dispersions of Polypyrrole-Silica Nanocomposites Using "Stringy" Silica Particles", J. Colloid & Interface Sci. 173, 135 (1995).

Glatzhofer, D. T., Cho, G., Chung, L. L., O'Rear, E. A., and Fung, B. M., "Polymerization and Copolymerization of Sodium 10-Undecene-1-yl sulfate in Micelles and in Admicelles on the Surface of Alumina", Langmuir, 9, 2949 (1993).

Nishizawa, M., Sawaguchi, T., Shibuya, M., and Uchida, I., "electrochemical Preparation of Ultrathin Polypyrrole Film at Microarray Electrodes", J. Phys. Chem. 95, 9042 (1991).

Wu, C. G., and Bein, T., "Conducting Polyaniline Filaments in a Mesoporous Channel Host", Science, 264, 1757 (1994).

Fig. 1. SEM of a dried ultrathin PPY film deposited TS-1 nanoparticles prepared using Self-assembled CPC bilayers.