Conductometry and Size Characterization of Polypyrrole Nanoparticles Produced by Ball Milling

Polypyrrole (PPy), one of the most extensively investigated conducting polymers, has attracted a great deal of interest because of its good electrical conductivity, environmental stability, and easy synthesis. PPy films were produced by polymerization of pyrrole and tosylate (TsO？) as dopants in the presence of oxidant FeCl3 and polyethylene glycol ( 8000) at ？5°C for 48？h. High energy milling was carried out at 850 rpm in the dry media with the balls of 10？mm. Particles were then characterized by Scanning Electron Microscope and Dynamic Light Scattering techniques for size distribution, and it was found that the size of PPy particles is a decreasing function of time of milling. Electrical conductivity was measured by preparing a homogenous aqueous dispersion of PPy particles and found as exponential decreasing function of time of milling. The changes occurred in PPy after milling was analyzed by Differential Scanning Calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). 1. Introduction Polypyrrole (PPy), one of the most extensively investigated conducting polymers, has attracted a great deal of interest because of its environmental stability and easy synthesis along with its good electrical conductivity [1]. Along with its other applications, PPy can be used as conducting filler in insulating polymer matrices in preparation of electrically conducting composites. These composites offer potentials in electronic packaging, EMI shields, display devices, electrodes, and other thermal applications [2–5]. Distribution of PPy particles in polymer matrices, however, becomes an issue. It has been reported that PPy nanoparticles can be effectively dispersed due to large surface area for reactions and highly porous in sol form [6, 7] and then they provide good conductivity. Recent studies also showed that the addition of polymers can influence the conductivity by steric stabilization of the polypyrrole chains [8]. To this end, water-soluble polymers of molecular masses over 20,000？g·mol？1, such as methyl cellulose, poly(vinyl alcohol-co-acetate), poly(ethylene oxide), poly(vinylpyrrolidone), poly(2-vinylpyridine), and poly(vinylmethylether), were studied. When using these additives, conductivities of a broad range ( –12？S·cm？1) have been obtained [8]. Specifically, for poly(ethylene oxide) with a molar mass of 130,000？g·mol？1, a conductivity of 2 × 10？3？S·cm？1 was found [9]. For this reason PEG 8000 was added in the preparation of PPy. Currently, various ways to produce PPy nanoparticles have been presented which can provide better electrical