Theory of orientational elasticity

Opto-Electronics Review

2008

Section: Introductionmentioning

confidence: 99%

Flexoelectric effect modelling

Opto-Electronics Review

2008

“…The inhomogeneity of the director field results in a distortion (elastic) free energy. In a continuum approach this energy is obtained as an expansion about an undistorted reference state with respect to gradients of the tensor order parameter Q [87][88][89] or gradients of the directors [90]. There are many equivalent forms of the biaxial elastic free energy and it is possible to transform one to another after making use of relations that follow from constraints imposed by the orthonormality of the directors.…”

Section: Static Distortions Of the Nematic Phasementioning

confidence: 99%

“…A general form of its density f d (r) was derived in [90] in the case of small distortions. When a considered phase has a D 2 symmetry group (the biaxial cholesteric phase) we get…”

Section: Distortion Free Energymentioning

confidence: 99%

Statistical Theory of Biaxial Nematic and Cholesteric Phases

2011

Acta Phys. Pol. A

A statistical theory of biaxial nematic and cholesteric phases is presented. It is derived in the thermodynamic limit at small density and small distortions. The considered phases are composed of short rigid biaxial or less symmetric molecules. The expressions for various macroscopic parameters involve the one-particle distribution function and the potential energy of two-body short-range interactions. The cholesteric phase is regarded as a distorted form of the nematic phase. Exemplary calculations are shown for several systems of molecules interacting via Corner-type potential based on the Lennard-Jones 12-6 functional dependence. The temperature dependence of the order parameters, the elastic constants, the phase twists, the dielectric susceptibilities, and the flexoelectric coefficients are obtained. The flow properties and defects in nematics are also discussed.

“…In a continuum approach the distortion free-energy density f d is obtained as an expansion about an undistorted reference state with respect to gradients of the vectors (L, M , N ). The form of the f d can be derived in many alternative ways but we use the form presented by Stallinga and Vertogen [27] (the surface terms are neglected):…”

Section: Elastic Deformations Of the Phasementioning

confidence: 99%

Flexoelectric Effect in Biaxial Nematics

2012

Acta Phys. Pol. A

The exoelectric eect provides a linear coupling between electric polarization and orientational deformation in liquid crystals. It inuences many electrooptical phenomena and it is used in some bistable nematic devices. A statistical theory of dipole exoelectric polarization in biaxial nematic liquid crystals is used to calculate temperature dependence of order parameters, elastic constants, and exoelectric coecients. The splitting of the two Meyer exoelectric coecients and the appearance of new exoelectric coecients is obtained at the uniaxial-biaxial nematic transition. The ordering of the split exoelectric coecients corresponds to the ordering of the split elastic constants.