Theory of Fluids, Phase Transitions, and Interfaces

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Benjamin Widom is supported by a grant from the Theoretical and Computational Chemistry Program to continue his work on the theory of fluids, phase transitions and interfaces. Work is proposed in three specific areas of research. In the first area of study, interfacial structure and interfacial phase transitions will be studied in an effort to understand the nature of the inhomogeneous region of contact between otherwise homogeneous fluid phases. In these studies a theoretical model will be used which should illuminate the connection, and resolve the differences, between two alternative and sometimes discrepant points of view, that of free energy functional theory and that of an interface displacement theory. The second area of study involves the coexistence of periodically modulated (liquid crystal) phases, and the structure and thermodynamics of the interface between such phases. A theoretical study will trace the evolution of the scattering peak in the isotropic fluid in which there is an incipient periodicity into a true delta function Bragg peak as the fluid undergoes a second order transition to an ordered, liquid-crystalline state. The third area of research involves the use of scaling theory to develop a model for the electrophoresis of charged, long-chain polymers. The proposed study will elucidate the interplay between the chain length of the polymer and the applied electric field. In the everyday world, interfaces between fluid phases are ubiquitous, yet very little is known about the details of the structure of the interface or the processes which are going on at the interface. Widom's work will provide molecular level insights on the spatial structure and thermodynamics of those contact regions.