Dynamics of Equilibrium Liquids, Supercooled Liquids, and Glasses

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Hans Andersen of Stanford University is supported by the Theoretical and Computational Chemistry Program to continue development of theoretical methods to calculate dynamical properties of liquids, supercooled liquids, and glasses at the molecular level. The basic strategy is to use a formally exact theory to create approximate kinetic theories of liquids, and then perform molecular dynamics computer simulations to test the accuracy of these approximations. Practical and accurate approximations capable of describing important physical processes that take place in low temperature liquids will be developed through this research. The specific objectives of this project include: (1) understanding and describing quantitatively the change that occurs in the dynamics of molecules as a liquid material is cooled and molecules become trapped for an extended period of time in a "cage" formed by its neighbors, (2) developing an understanding of how structural changes that take place in supercooled liquids can affect the dynamics, (3) understanding the variety of relaxation processes that take place and the relationships among them, and ultimately (4) understanding the very slow relaxation processes at very low temperature that lead to the formation of a glass at the glass transition. Glasses are technologically important materials made from a variety of components, both organic and inorganic, both low molecular weights substances and polymers. Examples include ordinary materials such as window glass and food containers, as well as advanced materials such as fiber optics for telecommunications, optical electronics, and solid electrolytes. The properties of these materials depend on how they are made, using methods that usually involves preparation of a high temperature liquids followed by various cooling and processing steps. The creation of optimal performance materials is currently guided largely by empirical observations. Design of rational processing procedures is expected to be enhanced by the increased understanding of dynamics of these materials and their corresponding liquids that will emerge from this research effort.