Second-order flexoelectric effect in chiral nematic liquid crystals

Abstract

A molecular–statistical model for the second-order flexoelectric effect in chiral nematics is developed, accounting for additional chiral terms in the pair intermolecular potential U(1,2). It is shown by symmetry analysis, that there are four independent chiral terms in the flexoelectric polarization, proportional to the square of director gradients, 𝒫∼λ∇n∇n. A molecular–statistical theory is developed for the second-order chiral flexoelectric constants λ. Their values, obtained in the mean-field approximation, depend on molecular dimensions, interaction parameters, and the degree of molecular chirality. Possible experimental situations are discussed where this effect can be observed.

Nonlinear flexoelectricity in noncentrosymmetric crystals

“…But still, the flexoelectric effect under a huge strain gradient, whereby a nonlinear response arises, is little studied. Considering the crystal symmetry, the second order flexoelectric effect which is described by seventh (odd) order tensor becomes non-zero if the system does not possess an inversion center such as piezoelectric or ferroelectric materials [14,26,27].…”