Kinetic Pathways to Phase Separation

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TECHNICAL SUMMARY:This award supports integrated research, education and outreach activities in theoretical condensed matter physics. The research investigates the dynamical changes in fluids when demixing into two or more fluid or solid phases. The theory and computer simulation of kinetics of phase separation for a variety of systems is the foundation of the research which emphasizes protein and colloidal solutions because of their technological and biomedical significance. The multiplicity of outcomes of phase separation, for example dense liquid droplets, gels, amorphous precipitates, polymer fibers and crystal nuclei, depends sensitively on the initial position in the phase diagram. Predicting the result of the separation process requires understanding the kinetic pathways available at the starting point and how the experimental conditions influence the evolution of a system undergoing this change. The project particularly emphasizes problems involved in protein crystal nucleation because of the importance of being able to grow high quality crystals in order to determine protein structure. Crystal nucleation is the bottleneck in growing high quality protein crystals. There are, in addition, innumerable industrial processes that involve colloidal suspensions and phase separation which are important and well characterized experimentally but largely without detailed predictive theoretical models.To further the theoretical basic understanding of kinetic pathways in phase separation processes the researcher will study several topics. The first topic is the effect of intermediate kinetic pathways, such as dense liquid droplets, on crystal nucleation and growth. A second topic is the effect of anisotropic molecular interactions in order to characterize the impact of highly directional, attractive interactions on the geometry of the critical nuclei and the nucleation barrier to nucleation. A third topic addresses the dependence of phase equilibria and nucleation rates on the concentration and type of agent commonly used to precipitate the solute molecules. The project employs theoretical methods to study the equilibrium and non-equilibrium properties associated with these subjects. Theories founded in statistical physics are employed along with Monte Carlo simulations, finite size scaling theory, transition path and umbrella sampling simulations and density functional theory.The project employs student researchers who are involved in undergraduate and graduate study in the sciences. The research contributes to their education in learning the theoretical techniques and understanding the properties of the materials and experience in the use of computational modeling to connect theory to prediction of materials properties. In addition, for the graduate students involved, the research forms the basis for dissertation work leading to the Ph.D.NON-TECHNICAL SUMMARY:This award supports integrated research, education and outreach activities in theoretical condensed matter physics. The research investigates the dynamical changes in fluids when demixing into two or more fluid or solid phases. The theory and computer simulation of kinetics of phase separation for a variety of systems is the foundation of the research which emphasizes protein and colloidal solutions because of their technological and biomedical significance. The multiplicity of outcomes of demixing or precipitation, for example dense liquid droplets, gels, amorphous precipitates, polymer fibers and crystal nuclei, depends sensitively on the initial conditions of the process and the constituent molecules. Predicting the result of the separation process requires understanding the dynamic processes available for the separation process and how the experimental conditions influence the evolution of a system undergoing this change. The project particularly emphasizes problems involved in protein crystal nucleation because of the importance of being able to grow high quality crystals in order to determine protein structure. Crystal nucleation is the bottleneck in growing high quality protein crystals. There are, in addition, innumerable industrial processes that involve colloidal suspensions and phase separation which are important and well characterized experimentally but in need of predictive theoretical models.To further the theoretical basic understanding of kinetic pathways in phase separation processes the researchers employ multiple theoretical tools. Theories founded in statistical physics are employed along with Monte Carlo simulations, finite size scaling theory, transition path and umbrella sampling simulations and density functional theory.The project employs student researchers who are involved in undergraduate and graduate study in the sciences. The research contributes to their education in learning the theoretical techniques and understanding the properties of the materials and experience in the use of computational modeling to connect theory to prediction of materials properties. In addition, for the graduate students involved, the research forms the basis for dissertation work leading to the Ph.D.