Quasielastic light scattering study of chemically crosslinked gelatin solutions and gels

Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde (GA) in the aqueous phase, where the gelatin concentration was fixed at 5% (w/v) and the GA concentration was varied from 1 x 10(-5) to 1 x 10(-3)% (w/v). The dynamic structure factor: S(q, t), was deduced from the measured intensity autocorrelation function, g(2)(tau), With appropriate allowance for heterodyning detection in the gel phase. The S(q, t) data could be fitted to S(q: t) = A exp(--D(f)q(2)t)t B exp(-t/tau(c))(beta), both in the sol (50 and 60 degrees C) and gel states (25 and 40 degrees C). The fast-mode diffusion coefficient, Dc showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, xi, of the crosslinked network exhibited strong temperature dependence, xi similar to (0.5 - x)(1/5) exp(-A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched exponential factor exp(--t/tau(c))beta. beta Was found to be independent of GA concentration but strongly dependent on the temperature as beta = beta(0) + beta(1)T + beta(2)T(2) The slow-mode relaxation time, t,, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found tau(c)(c) = tau(0) + tau(1)c +tau(2)c(2). Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state.