A molecular simulation study of a cyclic siloxane with attached biphehylyl 4-allyloxybenzoate mesogens

Abstract

A molecular simulation study of a cyclic siloxane macromolecule based on a pentamethylcyclosiloxane core and biphenylyl 4-allyloxybenzoate mesogenic units is reported. Molecular dynamics and semi-empirical calculations were used to provide insight into the conformation and the dielectric properties of the material. Out of three proposed conformations of the molecules, a cylindrical conformation was found to be the most probable. The intermolecular interactions were found to be optimized for the case where the mesogenic groups were planar and parallel to each other. The calculated mesogen length and inter-mesogen distances were consistent with available X-ray data. Electrostatic interactions were found to make a very significant contribution to the total energy. For the cylindrical model, the major component of the dipole was calculated to be along the long axis of the molecules. This is consistent with the alignment of the molecules parallel to a low frequency applied electric field as found experimentally.