Ultrasonic relaxation of agarose and carrageenan gels. The role of solvent

Abstract

By varying the polymer composition and the ionic environment ultrasonic relaxation spectra have been obtained for carrageenans in the following states of molecular organisation: (1) random coil solution, (2) isolated double helices, (3) aggregated helices, (4) soluble “domains” of unaggregated double helices linked through disordered single chain sequences and (5) continuous gel network formed by cross-linking of these domains by helix–helix aggregation. Agarose has also been studied in states (1) and (5) at the same temperature.

The results show that the strong relaxations observed in the gel state are a property of the overall network structure, rather than any of its components in isolation. From comparison of relaxation spectra obtained in deuterium oxide rather than water, and in the presence of urea and guanidine hydrochloride, we conclude that relaxation arises predominantly from motion of the solvent within the polymer network.