DECAY TIME DISTRIBUTIONS FROM DYNAMIC LIGHT-SCATTERING FOR AQUEOUS POLY(VINYL ALCOHOL) GELS AND SEMIDILUTE SOLUTIONS

Dynamic light scattering has been used to obtain decay time distributions for permanent poly(vinyl alcohol) (PVA) gels and the corresponding semidilute solutions by Laplace inversion of the autocorrelation functions. The gels were prepared from aqueous solutions of the narrow distribution polymer by cross-linking using glutaraldehyde. The PVA concentration range extends up to 7% w/v; parallel measurements were made on the gel and corresponding solution as a function of temperature between 3 and 55 °C. Two main relaxational modes typified the PVA solutions, both relaxation rates being diffusive. The fast relaxation characterizes the diffusive motions in the transient gel formed by interpenetration of molecular domains. The slow mode is considered to derive from “clusters” or (groups of chains) having a size that depends on concentration and only slightly on temperature. Formation of the permanent gel resulted in disappearance of the slow mode, and the gels were characterized by single-exponential correlation functions. At a given concentration, the polymer-polymer correlation length of the gel was almost twice that characterizing the transient network in the solution in spite of a very low cross-linking level (≈1%). In both systems the diffusion coefficient is linearly dependent on concentration. At high cross-linking density the correlation length shows a marked decrease. © 1990, American Chemical Society. All rights reserved.