Phase Separation of Viscous Ternary Liquid Mixtures

In this work we study the demixing of ternary liquid mixtures. Our theoretical model follows the standard diffuse interface model, where convection and diffusion are coupled via a body force, expressing the tendency of the mixture to minimize its free energy. This driving force induces a material flux which, in most cases, is much larger than that due to pure molecular diffusion. Here we model the behavior of a very viscous polymer melt, so that the Peclet number, expressing the ratio between convective and diffusive mass fluxes, is small. Two examples are presented, describing the phase separation of ternary mixtures in two and three phases, respectively, following an initial quench to an unstable state of their phase diagram. In the first case, as expected, we see that the growth of the domain size follows the well known diffusion-driven scaling, R(t) ∝ t. On the other hand, in the second example, the domain size growth follows the usual t scaling until the symmetry among the three phases breaks down and the domain size of ∗Corresponding author, email: [email protected] Preprint submitted to Chemical Engineering Science February 1, 2012 two of the three phases decrease sharply. After that point, the morphology of the system becomes more regular, almost crystal-like, and the three phases start to grow again, with the same growth rate R(t) ∝ t, with n = 0.11.