Contribution of rotational entropy to Frank elasticity

Abstract

Rotational entropy, or the entropy loss due to molecular alignment, has never been considered to contribute to Frank elasticity in previous molecular theories of nematic liquid crystals. Using a field-theoretical technique developed in polymer physics. we show that rotational entropy does yield Frank elasticity, which is attributed to the inherent non-local nature of orientational order due to the finite size of the molecules. We also give an exact cxpression of rotational entropy contribution to Frank elasticity for rod-like liquid crystals in terms of the orientational tensor order parameter.