Phase Segregation of Deeply Quenched Liquid Mixtures * Rajan Gupta, Roberto Mauri, and Reuel Shinnar Department of Chemical Engineering City College of City University of New York, NY, NY 10031 * After quenching a partially miscible liquid mixture deeply below its critical point of miscibility, we observed the formation of microdomains, which grew linearly in the range of 10-800 micron, indicating that phase segregation was driven by convection, and not by diffusion. While these domains were interconnected dendritic structures when the mixture had critical composition, they appeared to be spherical drops when the mixture was off-critical. When, instead, the mixture was initially segregated everywhere, with the exception of a millimeter-thick region, a sharp interface appeared few seconds after the quench, and only later did we observe the formation of drops larger than 10 micron. A simple analysis of the governing equations shows that, after an initial diffusion-driven stage leads to a non-uniform concentration field, a concentration-gradient-induced material flux is generated, which is orders of magnitude larger than its diffusive counterpart, and drives the successive process of phase segregation. The dominance of this antidiffusive material flux explains the additional experimental result that the separation rate is unaffected by the presence of emulsifying compound within the solution.