Nucleation and Spinodal Decomposition of Liquid Mixtures

We simulated the phase segregation of a metastable deeply quenched binary mixture. Our theoretical approach follows the diffuse interface model, where convection and diffusion are coupled via a nonequilibrium capillary force, expressing the tendency of the demixing system to minimize its free energy. As this driving force induces a material flux which, for liquid mixtures, is much larger than that due to pure molecular diffusion, the ratio of thermal to viscous forces is assumed to be of order 10^3, in agreement with experimental data. Using a pseudospectral method, we integrated the equations of motion in two dimensions, showing that the metastability of the system can be characterized through a critical radius, as in Gibbs’ treatment, or through the finite intensity of a white noise superposed on the initial uniform concentration field. This critical intensity grows exponentially as the mean composition of the mixture approaches its equilibrium value. In addition we showed that, in general, the value of the critical radius decreases as the number density of the nucleating drops becomes very large, so that nuclei have the chance to coalesce and grow before being reabsorbed.