Macromolecules, Vol.27, No.20, 5599-5608, 1994
Quasi-Elastic Light-Scattering Study on Solutions of Linear Flexible Polyelectrolytes at Low Ionic Strengths
Dynamic light scattering measurements have been performed on aqueous solutions of linear poly(ethyleneimine), poly(2-vinylpyridine), and sodium poly(styrenesulfonate), all flexible polyelectrolytes, at several polymer concentrations above the overlap concentration c* and over a wide NaCl concentration range. A change in the shape of the intensity correlation functions (ICFs) of the scattered light from a monomodal to a bimodal decay is observed with an increase of the polyelectrolyte concentration and a decrease of the NaCl concentration. The decay rates of the monomodal ICFs and the fast decay rates of the bimodal ICFs are related and can be explained by the cooperative diffusion in a transient polyelectrolyte network. The slow mode of the bimodal decay can be removed by filtration, disappears for some solutions spontaneously after a given time, and, for solutions of linear poly(ethyleneimine), exhibits hysteresis depending on the way the NaCl concentration has been established. It is concluded that the slow mode is related to clusters of polyelectrolyte chains which are apparently formed in solutions with a high polyelectrolyte concentration and low concentrations of added NaCl.
Keywords:ELECTROLYTE SALT-SOLUTIONS;MOLECULAR-WEIGHT;MOLAR-MASS;SCALING RELATIONS;POLY(METHACRYLIC ACID);POLY(ETHYLENIMINE);DIFFUSION;DYNAMICS;REGIME;POLYSTYRENE