INFLUENCE OF POLYELECTROLYTE ADSORPTION ON THE ELECTROOPTICAL BEHAVIOR OF AEROSIL PARTICLES

The adsorption of polyelectrolyte, sodiumcarboxymethyl-cellulose (Na-C MC) on Aerosil (SiO2) particles is studied by means of electric light scattering and electrophoresis. The electro-optical effect alpha incre ases with the rise of polyelectrolyte concentration. Simultaneously th e increase of particles' electrophoretic mobility reveals the adsorpti on of polyion on identically charged particles. The similarity of the frequency dependence of the electrooptic effect at different polyelect rolyte concentrations is an indication that the particles' induced dip ole moment is mainly determined by polyelectrolyte' counterions behavi our. Two relaxations of the electro-optical effect are observed at fre quencies ranging from 500 Hz to 100 kHz - the first relaxation is abou t 1 kHz, the second one - in the 10 kHz region. The increase of charge density parameter xi doesn't influence the first relaxation, but the second one becomes wider and more noticeable. According to Manning pre dictions the rising of xi (xi > 1) results in the increase of the frac tion of diffuse counterions. So their contribution to the induced dipo le moment is more clearly demonstrated in the frequeny dependence. Mos t probably the first relaxation of alpha is connected with the ''bound '' counterions whereas the second is due to the diffuse counterions. I n the case of polyelectrolyte adsorption pn the particles of the same charge sign an analogy with Manning consideration for free polyelectro lytes in solution could be drawn.