EFFECT OF COUNTERION SPECIES ON THE DYNAMICS OF POLYSTYRENESULFONATE IN AQUEOUS-SOLUTION AS STUDIED BY DYNAMIC LIGHT-SCATTERING

The diffusion behavior of macroions in aqueous solutions especially at low salt concentrations has been interesting and also mysterious prob lem since Schurr cf al. found slow mode in 1978. By the systematic inv estigations on the structure and dynamics of charged particles and mac romolecules in solution, it has been suggested that some novel factor( s) should be taken into account for understanding of interesting pheno mena in these systems. In this study, the dynamic character, i.e., dif fusion behavior of polystyrenesulfonate (PSS) in aqueous solution has been studied by dynamic light scattering (DLS) as a function of salt c oncentration in various salt forms. Both fast and slow modes were clea rly detected. With increasing salt concentration, the fast mode became dominant and its decay rate became slower. On the other hand, the slo w mode was not so sensitive to salt concentration but its contribution markedly decreased with increasing salt concentration and then became almost negligible at higher salt concentrations. The fast mode of LIP SS, NaPSS, and CsPSS was in the order of LiPSS less than or equal to N aPSS<CsPSS, although the difference was small, and was consistent with the order of diffusion coefficients of counterions. The fast mode of HPSS was much faster than that of other PSS salts. The same tendency w as also observed for HPES and NaPES, salts of polyethylenesulfonate. T he slow mode also depended on the counterion species, which may predic t the important role of counterion dynamics in electric interaction be tween macroions. (C) 1998 American Institute of Physics.