Dilute solution behaviour of polyacrylamides in aqueous media

The dielectric behavior of cationic, anionic and nonionic polyacrylamide aqueous solutions was monitored. The magnitude of dielectric increments of the polymer solutions were found to depend upon the type of the dipole and its alignment along the chain, pH of the media and the polymer concentration. The hydrolysis of the amide moieties in the alkaline media was found to affect the conformations of the highly charged cationic polyacrylamide by enhancing inter-unit interactions between the cationic and carboxylic moieties. Similarly, the dielectric constant increments of the nonionic polyacrylamide were found to become smaller in the alkaline conditions in contrast to very high values in the acidic conditions. The viscosity behavior showed the extended form of conformations in the chains as evidenced by the observed large reduced viscosities when inter-unit repulsion was dominant and while the presence of inter-unit attractions in the chain was characterized by smaller reduced viscosities. A systematic decrease in the intrinsic viscosities of polymer solutions was noted both in acidic as well as alkaline media with the addition of salt. The isentropic compressibilities of the polymer solutions under the same conditions showed a declining trend with the increasing salt concentrations suggesting the increased compactness of the chains. (C) 1998 Elsevier Science Ltd. All rights reserved.