DYNAMIC LIGHT-SCATTERING FROM BINARY-MIXTURES OF POLYELECTROLYTES - I- INFLUENCE OF MIXING ON THE FAST AND SLOW POLYELECTROLYTE MODE BEHAVIOR

Dynamic light scattering experiments were performed on salt-free aqueo us binary mixtures of sodium poly(styrene sulfonate) with different mo lecular weights. Three diffusive modes were observed and investigated as a function of the mixture composition, total polymer concentration, and molecular weights of the components of the mixture. The fast and slow polyelectrolyte modes, which are typical for binary polyelectroly te solutions, are observed also in binary mixtures and maintain their basic characteristics. The fast diffusive mode is independent of the t otal polymer concentration, mixture composition, and molecular weights of the two components, in agreement with results obtained on binary s olutions. Only one slow diffusive mode is observed in binary mixtures, in spite of the fact that polyions with appreciably different molecul ar weights in binary ablutions give slow modes on appreciably differen t time scales. Therefore, the slow polyelectrolyte mode cannot be iden tified with any single-chain property. Oppositely, our results confirm ''multichain character'' of the processes behind the slow mode mechan ism. In addition to the fast and slow polyelectrolyte modes, a new mod e, named the ''medium mode,'' was observed. The investigation of the m edium mode is presented in the subsequent paper in this issue of the j ournal. (C) 1997 American Institute of Physics.