Molecular-statistical model for the nematic phase of semiflexible dimers

(Received 25 March 1992, accepted in final form 23 October 1992)

Abstract
A microscopic model is developed to describe properties of a nematic phase consisting of semiflexible dimers. The effect of the chain bonding the two mesogens is described by the local conditional probability of their mutual orientation in terms of a bare stiffness parameter , assuming an even number of carbon atoms in the chain. In the framework of a molecular field approximation we obtain a complete statistical description of the nematic with expressions for order parameter, mean-field potential, free energy and phase transition parameters. The width of the N-I transition hysteresis is in agreement with observed values. Comparison with data on the transition temperatures in three series of nematogenic dimers enables us to obtain the quantitative dependence of the rigidity on the length of the (CH ₂)_n chain connecting the two monomers.