Chain ordering in liquid crystals. I. Even-odd effect

In the liquid crystalline phases of many organic materials molecular end chains take part in the ordering process. For a single chain, this ordering is calculated by exact summation over all conformations of a chain in the molecular field due to the neighboring molecules. The nematic orientational ordering of a system where molecules consist of rigid parts and chains is then obtained within a self-consistent molecular field approximation. The results are in very good agreement with the experimental phase diagrams for homologous series of liquid crystals, and for the first time provide the explanation for the well known even-odd effect in isotropic-nematic transition temperatures. In agreement with observations, the corresponding transition entropies exhibit both the increase with increasing end-chain length and the even-odd variations. The decrease of order along the chain is also calculated and compared with the available data.