Molecular theory of the tilting transition in smectic liquid crystals with weak layer contraction and diffused cone orientational distribution

Osipov, Mikhail and Pajak, Grzegorz (2012) Molecular theory of the tilting transition in smectic liquid crystals with weak layer contraction and diffused cone orientational distribution. Physical Review E: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 85 (121701). 021701. ISSN 2470-0053 (https://doi.org/10.1103/PhysRevE.85.021701)

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Abstract

A molecular field theory of the smectic-A−smectic-C transition has been developed for smectics with a diffused cone orientational distribution of molecules (volcano-like distribution function) in the smectic-A phase and anomalously weak layer contraction in the smectic-C phase. Orientational order parameters and smectic layer spacing have been calculated numerically as functions of temperature and compared with the results obtained using a model with a standard Maier-Saupe–type distribution function that has been considered before. A molecular theory of the electroclinic effect in chiral smectics has also been developed using the recently proposed simple biaxial interaction potential. A comparison has been made between the absolute values and temperature variations of the electroclinic coefficient obtained using the volcano model, the model with Maier-Saupe–type distribution, and the orthodox cone model proposed by de Vries. It has been shown that the model with a conventional “sugar loaf” type orientational distribution function in the smectic-A phase is sufficient to describe the main properties of smectics with anomalously weak layer contraction.