Chemical and physical hydrogels: two casesystems studied by quasi elastic light scattering

A chemical hydrogel based on telechelic poly(vinyl alcohol) and a physical synergic hydrogel, xanthan–glucomannan, were studied by means of dynamic light scattering technique. Two different nonergodic methods, due to Pusey et al. (Physica A 157 (1989) 705, Phys. Rev. A 42 (1990) 2161) and Xue et al. (Phys. Rev. A 46 (1992) 6550), were used to obtain the correct dynamic structure factors f(q,t). Good agreement between the results obtained with the two procedures was found. The behavior of the f(q,t) for different q vectors is consistent with the hypothesis that the nonfluctuating component in the scattered light is not due to microscopic heterogeneities but to restricted motion of the scatterers. The model of Krall et al. (Phys. Rev. Lett. 80 (1998) 778, Physica A 235 (1997) 19) was successfully applied to both hydrogels to extract the characteristic parameters of the network from the f(q,t) functions.