Microscopic one-particle description of reentrant behavior in nematic liquid crystals

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Abstract
Reentrant behavior in nematic liquid crystals is described by the treatment of the system as a mixture of monomers and dimers interacting through attractive induced soft interactions as well as hard-core repulsions. It is shown that the induced forces between dimers, monomers, and between monomers and dimers, respectively, under suitable conditions of temperature and density lead to a smectic layer structure with a period equal to the length of the dimer. However, with decreasing temperature or increasing density, repulsive steric forces, due to the unfavorable packing of the dimers in the smectic planes, may take over and thus favor the nematic phase again. In agreement with experiment the best conditions to get a reentrant nematic phase are predicted for the ratio of the length of the dimer to that of the monomer between 1.3 and 1.4. The predictions of the model are in good agreement with currently available experimental data. In principle, the model applies also to discotic liquid crystals.