Dielectric relaxation in aqueous solutions of polymers

Abstract

Complex permittivity measurements on aqueous solutions of non-ionic linear heterohydrocarbon polymers are summarized. The solutes include poly (ethylene oxide), poly (vinyl alcohol), poly (vinyl methyl ether), poly (ethylene imine), poly (acrylamide), poly (methacrylamide), and poly (vinyl pyrrolidone). The measured dependence of the complex permittivity on frequency is discussed in terms of a model of the solutions to yield the hydration number and reorientation time of disturbed water molecules as well as the relaxation time and the molar dielectric increment of the solutes. The hydration water data are compared to those of oligomers and of small organic molecules for the purpose of gaining insight into the effect of molecular size, shape, and flexibility on the dynamics of the surrounding water. The molar dielectric increment of the solutes is analyzed to show that with the polymers there is some hindrance of the motions of polar components as compared to a free rotation within the chain backbone. With the poly (ethylene imine) solutions an additional contribution to the complex permittivity is suggested which seems to reflect the diffusive axial motions of OH− counterions along the weakly protonated polymer chains.