Critical dynamics in the presence of a silica gel

Dynamic and static light scattering results are reported for isobutyric acid and water in a 4 wt. % silica network with a crossover length of 300 Å. In the one-phase region, well away from the critical point, the decay rate for order parameter fluctuations is unaffected by the network. Near the critical point, the order-parameter correlation function is well fitted by the sum of an exponential with decay rate ${\mathrm{\Gamma }}_1$ and a term of the form exp[ln(τ/${\mathit{t}}_0$)/ln(${\mathrm{\Gamma }}_2$ ${\mathit{t}}_0$)${]}^3$, with ${\mathrm{\Gamma }}_2$≃${\mathrm{\Gamma }}_1$. When the system reaches conditions where the correlation length of the pure system is ∼100 Å, it spontaneously orders.