ABSTRACT CTS-9634324 In recent years, the authors have developed solvent extraction processes that are based on phase separation of partially-miscible solvent mixtures. During this work it was found that under certain circumstances, when two rapidly miscible solvents are heated above critical temperature and then rapidly cooled at a temperature below their co-existence curve, phase separation is extremely rapid, even in the presence of emulsifiers and impurities that tend to slow down coalescence. There is considerable experimental evidence in our previous work indicating that separation occurs by spinodal decomposition and not by conventional nucleation and growth. In addition, the possibility of phase separation without nucleation at the submicron scale was further supported by our theoretical work. What still remains to be explained is why, after a deep temperature quench, phase separation leads to the formation of large, millimeter-size drops, as opposed to the micron-size drops that are formed as a result of very small quenching. The explanation of this quite fascinating phenomenon is one of the main objectives of our proposed research. The formulation of a theory of phase separation of deeply quenched systems remains a major challenge. Almost all the experimental and theoretical works on spinodal decomposition have considered only very small temperature quenches (i.e. 0.1(C at most) from the critical point, often assuming that other effects due to temperature inhomogeneties could be simply superimposed. However, one of the results of our work dealing with the phase separation of deeply quenched (i.e. ( 10(30(C) below the critical point) systems, is that this "superposition" approach is not correct. In fact, instead of the small, mircron-size drops that form as a result of "classical" spinodal decomposition, we observed the formation of large, millimeter-size drops. Now, if these large drops were initially small, and then grew by diffusion and coalescence (as the "classi cal" theory would suggest), then their growth would be heavily retarded by the presence of any surface-active compounds within the system. On the other hand, we observed that phase separation of deeply quenched systems is fast, independently of the presence of such compounds. A complete explanation of the phenomenon is not available at present, although our theoretical model does offer some encouraging results in that direction. What is needed, however, is not only more theoretical work, but also visual observations of the phenomenon at much shorter timescales than we were able to do till now. This experimental work is the main subject of the current proposal, and includes the construction of an experimental setup that will allow us to study the phase separation in a continuous, steady state apparatus, overcoming the difficulties encountered in the past to observe the initial, fast stage of the phenomenon. The proposed research will lead to a better understanding of spinodal decomposition. In addition, it has applications in the development of improved solvent extraction processes both in biotechnology and in the extraction of metal ions from contaminated soils, sediments and sludges, using chelating agents that are soluble in organic solvents. ***
