QUASI-STATIC DOMAINS IN PLANAR NEMATIC LIQUID-CRYSTALS AROUND THE DIELECTRIC INVERSION POINT

A simple viscoelastic approach is proposed to describe the periodic pa tterns, characterized by static walls and splay-bend distortion, which appear in samples of nematic liquid crystals having dielectric anisot ropy epsilon(a) dependent on the frequency. The modulated structure, r esulting from a steady velocity field v coupled with a steady director field n, is achieved when an electric field is applied normally to th e plates of a planar unidirectional nematic cell. Such a kind of quasi static domain is theoretically investigated not only in the frequency region, where the usual aperiodic Freedericksz effect becomes unfavora ble, Re(epsilon(a)) still being positive, but also where Re(epsilon(a) ) < 0, favoring in principle the initial orientation. Both previous si tuations are considered in the vicinity of the sign reversal point. Th e present model describes the dielectric loss near the reversal point in terms of the appearance of the corresponding effective space charge , which interacts with the effective electric field, causing a steady electrohydrodynamic motion of very small amplitude inside the nematic liquid crystal layer. As a result, a quasistatic tilted modulated stru cture emerges, with wave vector parallel to the initial planar orienta tion of the nematic cell.