PARTICLE-SIZE DISTRIBUTIONS OF POLYANILINE SILICA COLLOIDAL COMPOSITES

We have characterized a new polyaniline-silica composite colloid by various particle sizing techniques. Our transmission electron microscopy studies have confirmed for the first time an unusual "raspberry" morphology, with the small silica particles held together by the polyaniline "binder". These particles have average diameters in the size range 150-500 nm. Charge-velocity analysis experiments indicated a number-average particle diameter of 300 +/- 80 nm, but only poor statistics were obtained (172 particles counted). Photon correlation spectroscopy studies suggested an intensity-average particle diameter of 380 nm. Disk centrifuge photosedimentometry (DCP) turned out to be our preferred sizing technique for the polyaniline-silica colloids, since it was both quick and reliable and, more importantly, produced the true particle size distribution(PSD) curve with excellent statistics. The DCP data indicated a weight-average and number-average particle diameter of 330 +/- 70 nm and 280 +/- 70 nm, respectively, and moreover confirmed the PSD to be both broad and unimodal. Finally, these colloidal composites were sized using the Malvern Aerosizer. Using this instrument in conjunction with a nebulizer attachment (which allowed particle sizing of the "wet" dispersion) rather than in the conventional "dry powder" mode, we obtained particle size data which were in reasonable agreement with the DCP results.