POLYANILINE DISPERSIONS .6. STABILIZATION BY COLLOIDAL SILICA PARTICLES

Aniline was polymerized in the presence of ultrafine colloidal silica particles (hydrodynamic diameter 35 nm) in aqueous media and, given a sufficient silica concentration, colloidally stable polyaniline-silica particles were obtained. The particle size of the resulting dispersio ns was determined by both dynamic light scattering and disk centrifuge photosedimentometry. The typical size of these polyaniline-silica par ticles is in the range 300-600 nm and is insensitive to the concentrat ion of components in the reaction mixture, temperature, or acidity of the reaction mixture. Particles produced at 0 degrees C are spherical and their shape becomes less defined when polymerization proceeds at 2 5 degrees C. As the silica size is increased, the composite particles become larger and their raspberry morphology more distinct. The electr ical conductivity of a typical polyaniline (37.8 wt%)-silica composite is 6.1 x 10(-2) S cm(-1) at 25 degrees C. It grows with increasing te mperature and does not depend on the frequency in the investigated ran ge from 20 Hz to 1 MHz.