Effect of counter ion valency on dynamics of sodium sulfonated polystyrene

We have studied the effect of counter ion valency on the chain dynamics of sodium sulfonated polystyrene polyelectrolyte having molecular weight, 1000 kDa. We have investigated the chain conformations as a function of counter ion valency and salt concentration using Dynamic Light Scattering. In the absence of added salt the polyelectrolyte assumes an extended structure. With addition of salt the hydrodynamic radius of the polyelectrolyte decreases on account of the screening effect of the added salt ions that effectively reduces the electrostatic repulsion between the like charged monomer units. With increase in ionic strength the polyelectrolyte chain acquires a coil like conformation. Reduction in size of the chain in presence salts having higher valency occurs at a much lower salt concentration as compared to monovalent salts