ABSTRACT CTS-9409856 University of Wisconsin Madison P.I.: Arun Yethirajo Recent advances in computer simulation algorithms and liquid state theory have made possible a microscopic study of flexible polymer melts and solutions. The purpose of the proposed work is to extend these methods to the study of liquid crystalline polymers. Using computer simulation and density functional theory, a fundamental understanding of the phase behavior of these systems is sought, thus assisting the engineering of new polymers for specific applications. Monte Carlo simulations of dense melts of polymers will be performed using first a simple semiflexible chain model and then more realistic rotational isomeric state models. These simulations will be used to test the approximate theories and suggest new approximations if necessary. Several theoretical approaches will be investigated. These will include an Onsager theory with a renormalized self-consistent intermolecular potential, and a density functional theory with an excess free energy functional obtained via an extension of the generalized Flory theory of fully flexible polymer melts to nematic fluids. There are several aspects to the proposed research. (i) Large scale computer simulations will be performed in conjunction with the investigation of approximate theories thus allowing for considerable interfacing between the two. (ii) Some of the most difficult aspects of the theories will be performed exactly via simple two molecule computer simulations. (iii) Theoretical techniques will be developed that are equally applicable to both thermotropic and lyotropic liquid crystalline polymers. (iv) Chemically realistic models will be investigated which will facilitate comparison with experiment without adjustable parameters. If successful, the theories could be useful for the design of new materials by providing means of predicting the equilibrium properties from the chemical structure. The possible disadvantage of our pr oposed work is that the techniques we hope to develop might prove to be too computationally intensive for routine use in industry. Even so, we will have obtained valuable insight into the behavior of liquid crystalline polymers that should assist the design of new materials.
