(439f) Effects of Water Droplet Size On Polypyrrole Particle Synthesis Using Water in Oil Emulsion System

Conducting polymers such as polyacetylene, polyaniline, and polythiophene have been investigated widely for use in various applications. Polypyrrole is one of the most studied conducting polymers because of its environmental stability and relative ease of synthesis. However, the poor processability of PPy is often a problem. Particularly for this reason, the synthesis of a fine-particle conducting polymer by chemical oxidative polymerization is a valuable synthetic goal for applying the conductive nano filler. Normally, PPy particles are obtained by chemical polymerization in various organic solvents and aqueous media, into which an oxidative agent such as ferric chloride, ferric perchlorate, potassium persulfate, or ammonium persulfate is added. However, this process yields not only spherical particles, but also particles that are hexagonal, cubic, wire-like, and ribbon-like. As the rate of reaction in chemical oxidative polymerization for the synthesis of conducting polymers is very rapid, it is important to prepare spherical particles of the conducting polymer to maintain the reaction temperature at approximately 278 K. In this study, control of the reaction rate was investigated, and a new method for the synthesis of polypyrrole particles using water in oil emulsion is proposed. In this system, the diffusion of the monomer into a water droplet as the dispersed phase is the rate-determining step, and controls the reaction rate at room temperature. Monodispersed spherical polypyrrole particles were synthesized at room temperature using this method. The effects of organic solvent as the continuous phase on the synthesized polypyrrole particle size were investigated. The diameter of the polypyrrole particle decreased with increasing viscosity of the organic solvent, and an empirical formula connecting the diffusion coefficient and average particle size is proposed. In addition, the effects of the volume fraction of the dispersed phase on the water droplet size of emulsion and synthesized polypyrrole particle size were investigated. The water droplet size increased with increasing volume fraction of the dispersed phase. On the other hand, the tendency of the particle size differs from water droplet size. In the condition that the volume fraction of dispersed phase was smaller than 10%, the water droplet size of emulsion was around 10 nm, and it is considered reversed micelle. Therefore, the polypyrrole particle formation mechanism changes with water droplet size. From these results, we reveal that monodispersed spherical polypyrrole particles were synthesized at room temperature by chemical oxidative polymerization using W/O emulsion system. And, the polypyrrole particle formation mechanism was proposed.