Spontaneous double phase separation induced by rapid hydrodynamic coarsening in two-dimensional fluid mixtures

We demonstrate by numerical simulations that spinodal decomposition of fluid mixtures is strongly dependent upon their "fluidity," which characterizes the relative importance of the two relevant transport mechanisms, hydrodynamic flow and diffusion. Thus, it may not be "universal," at least in two dimensions. For a high fluidity, we find "spontaneous double phase separation." We confirm that this unusual phenomenon is caused by the following mechanism: High fluidity causes rapid geometrical coarsening of domains due to a hydrodynamic process, which is too fast for diffusion to follow. This brings the system out of equilibrium and induces secondary phase separation.