American Chemical Society, Langmuir, 23(16), p. 8585-8594, 2000
DOI: 10.1021/la000089m
Full text: Unavailable
Aqueous gelatin slowly cooled from the sol state (60 °C) to different temperatures around the gel point has been investigated using dynamic light scattering. Three modes of correlation decay have been observed and their dependence on scattering vector (q), concentration (c), and temperature interpreted in the light of existing theories. The c dependence of the fast mode's q-independent diffusion coefficient gives information about excluded volume effects and cross-link density. The slowest mode is related to the transient network lifetime. Close to the sol−gel transition, its q-independent relaxation time increases by orders of magnitude and its amplitude decreases. The intermediate mode, the frequency of which increases linearly with q3, is assumed to be due to cross-link density heterogeneities which are present in the nonideal gel. The slowing down of this mode on approaching the gel point gives rise to quenched fluctuations of cross-linking density which may be responsible for the increase in “extra” scattering intensity observed at small q vectors in permanent gels (Picot−Benoît effect).