Effects of gelation on spinodal decomposition kinetics in gelatin

Abstract

We have studied the kinetics of spinodal decomposition in a gelatin-water-methanol mixture, which undergoes a sol-gel transition simultaneously with phase separation, using light scattering techniques. The kinetics of the sol-gel transition was investigated using falling-ball microviscometry techniques. We found that the kinetics of phase separation depend very strongly on temperature; and for deep quenches, where the rates of phase separation and gelation are comparable, the phase-separation process does not go to completion. Prior to the onset of gelation the initial growth rate of the structure factor can be described according to the Cahn-Hilliard model, even though the wavevector at maximum scattered intensity decreases as km ∼ t−0.6. For deep quenches after the onset of gelation, km remains unchanged with time, while the peak intensity exhibits a slow growth. The final domain size, k−1final, at which the phase-separating morphology becomes pinned decreases with increasing quench depth. Micrographs of the phase-separated domains reveal a connected structure on length scales of a hundred micrometres superimposed on a finer network structure due to gelation.