Interference of phase separation and gelation: A zeroth-order kinetic model

We propose a Ginzburg-Landau-type model to describe the kinetics of mixtures undergoing a sol-gel transition (nonconserved order parameter) simultaneously with phase separation (conserved order parameter). We compute the temporal development of the structure factor and determine the wave vector ${\mathit{q}}_{\max }$ at which the structure factor is maximal. We find that after a certain time ${\mathit{t}}_{\mathit{f}}$, ${\mathit{q}}_{\max }$ saturates at a final value ${\mathit{q}}_{\mathit{f}}$, and we calculate the temperature dependence of both ${\mathit{t}}_{\mathit{f}}$ and ${\mathit{q}}_{\mathit{f}}$. The predictions of this zeroth-order model agree remarkably well with recent kinetic measurements in gelatin-water-methanol mixtures.