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

A chemical hydrogel basedon telechelic poly(vinyl alcohol) anda physical synergic hydrogel, xanthan-glucomannan, were studied by means of dynamic light scattering technique. Two di1erent nonergodic methods, due to Pusey et al. (Physica A 157 (1989) 705, Phys. Rev. A 42 (1990) 2161) andXue et al. (Phys. Rev. A 46 (1992) 6550), were usedto obtain the correct dynamic structure factors f(q; t). Goodagreement between the results obtainedwith the two procedures was found. The behavior of the f(q; t) for di1erent q vectors is consistent with the hypothesis that the non6uctuating component in the scatteredlight is not due to microscopic heterogeneities but to restrictedmotion of the scatterers. The model of Krall et al. (Phys. Rev. Lett. 80 (1998) 778, Physica A 235 (1997) 19) was successfully appliedto both hydrogels to extract the characteristic parameters of the network from the f(q; t) functions.