ELECTROOPTIC STUDY OF OXIDE PARTICLES IN HYDROLYZED POLYACRYLAMIDE SOLUTIONS

Electric light scattering by aqueous ferric oxide suspension (beta-FeO OH) is investigated as a function of the concentration and degree of h ydrolysis of polyacrylamide (HPAM), The kilohertz electro-optical effe ct (alpha(s)) connected with ion polarization in the diffuse part of e lectric double layers of particles decreases with increasing HPAM conc entration, It falls to zero near to the isoelectric point of particles and increases again after surface recharging to a value that does not change with further polymer concentration increase. alpha(s) is shown to be independent of HPAM charge density in stabilized suspensions, I n contrast, the variations of the low frequency effect (at hertz frequ encies) after the isoelectric point of particles correlate well with t he charge of macromolecules. Similarity between the frequency behavior of the electro-optical effect in stabilized suspensions and the diele ctric dispersion of polyelectrolyte solutions is noted. The hydrodynam ic thickness of the adsorbed layer, obtained from electric light scatt ering, is found to be independent of the charge of macromolecules in s tabilized suspensions. Its value (L(r) similar to 10 nm) is 5-6 times smaller than the thickness of the adsorbed uncharged polyacrylamide, i ndicating a flatter conformation of the adsorbed polyelectrolyte molec ules. (C) 1996 Academic Press, Inc.