The Molecular Theory Of Thin Nematic Liquid Crystal Films Consisting Of Polar Molecules

Since ihe pioneering work of Onsager, Flory, and Maier and Saupe, many theoretical physicists have devoted themselves to the work on improving and perfecting molecular statistical theory on the basis of a large of experimental results, such as Chandrasekhar, Humphries, Luckhurst, Gelbart, Baron, Cotter. Due to the nonlinearity and complexity of many-body problems, the molecular statistical theory of liquid crystals has not been perfect as yet. At present, liquid crystals are widely used to optical display devices. The structure and properties of interfacial region of liquid crystals (i.e the layers adjacent to a solid walls) are obviously affected by the solid walls. Therefore, the investigations of interface properties of liquid crystals have significance of theory and extensive prospect of applicationIn this paper, the molecular field theory and a two-particle cluster theory are presented to study thin nematic liquid crystal films confined by two type solid substrates, respectively. The nematic liquid crystals (NLCs) consist of polar molecules. Our fundamental works are presented as follows:Part I: A new surface potential form is proposed to describe the action of rubbed substrate to liquid crystal molecules. The author is the first to apply the molecular field theory to investigate liquid crystal films confined by rubbed substrates, liquid crystal films consisting of polar molecules. Our main conclusions are that surface polar interaction can give rise to a transition from a high temperature homogeneous alignment to a low temperature hometropic alignment, that if the strength of the surface polar interaction is weaker than the one of surface dispersion interaction, the homogeneous alignment of the nematic is always stable.Part II: A two-particle cluster theory is presented to study the effect of a solid bounding surface on the NLCs formed by polar molecules. We develop a function iterative method to solve the complicated equation for the uneven nematic molecular orientational distribution function. The theoretical results show that a thin polar layer can be arised at the NLC-solid interface. As the action of the solid bounding surface is strong enough, the surface polar ordering is almost independent of temperature and unaffected by the phasetransitions in the bulk of the NLCs.These studies have significance for thoroughly understanding of the interface property and surface property of liquid crystals in the molecular level.