Phase Transitions in Nanosystems: Effects of Surface, Importance of Fluctuations.

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Professor Howard Reiss is supported by the Theoretical and Computational Chemistry Program to perform research on phase transitions in nanoscale systems. Particular emphasis is on surface effects and on the role of fluctuations. Theoretical tools include thermodynamics, statistical mechanics and density-functional theory. For technologically interesting systems where accurate molecular-level knowledge and/or intermolecular potentials are unavailable, an enhanced liquid-drop model is developed and applied. This method relies on measurable macroscopic thermophysical quantities such as surface tension, density and vapor pressures. Problem areas under consideration include cluster nucleation processes, phase transitions in clusters, atmospheric aerosols, fluids confined to nanopores, and capillary condensation of fluids. Nucleation is one of the most ubiquitous phenomena in all of science and technology. Despite its importance, the theory of nucleation has until recently been phenomenological. The formulation of a coherent, consistent theory of molecular nucleation has important consequences for many practical applications in atmospheric science and in nanoporous and mesoporous materials. With respect to the former, solidification of cloud droplets is relevant to ozone depletion in the upper atmosphere. With respect to the latter, nano- and meso- porous systems are used in a variety of industrial processes such as chemical separation and sequestration, absorbent materials, catalysis and oil recovery. As further progress is made in synthesis of molecular sieves and nanotubes a more complete understanding of surface effects will be necessary. Graduate and postdoctoral training is accomplished in concert with the research