Parallel and cross-like domains due to d.c. and low frequency (< 2 Hz) electric fields in nematic liquid crystal layers with negative dielectric anisotropy

Abstract

2014 On étudie les domaines parallèles et croisés obtenus par application de champs électriques continus et basse fréquence ( 2 Hz) sur des cristaux liquides MBBA et 440 à anisotropie de susceptibilité diélectrique négative. Les principaux résultats sont : 2014 la reproductibilité des domaines parallèles particulièrement pour des couches inclinées d'épaisseur 5-90 03BCm avec un ancrage faible assuré par un agent tensio-actif (savon) ; 2014 la création de domaines en croix dans des couches minces homéotropes ; ces domaines apparaissent dans la région de la cathode et sont dus au fort champ inhomogène générateur de structures flexion-éventail séparées par des disclinaisons.Parmi les mécanismes électrostatiques et électrodynamiques connus, seul l'effet flexoélectrique dû à un gradient de champ électrique peut expliquer la formation de ces domaines.

Surface-Induced Flexoelectric Domains in Asymmetrically Strong-Weak Anchored MBBA Films

“…The ratio pld, where p is the domain period and d the thickness of the film, decreases with increasing d up to 150 m in accordance with the experimental results obtained for weakly-anchored MBBA layers [12] while the threshold voltages, higher for thinner cells and lower for thicker cells, w r ere very different from those measured for weakly-anchored MBBA layers (Figs. 2 and 3) [12]. Of special interest are the surprisingly-small threshold voltages: 1.5-2 V obtained with thick MBBA cells.…”

“…The Unauthenticated Download Date | 5/13/18 7:07 AM different from that described in [12]. We noticed that the efficiency of the soap deposition was higher when rubbing on with a cloth.…”

“…The strong-weak anchoring of the LC layer made possible the creation of surface-induced domains for thicknesses up to 210 fj.m, which was not achievable with weakly-anchored MBBA layers [12]. The ratio pld, where p is the domain period and d the thickness of the film, decreases with increasing d up to 150 m in accordance with the experimental results obtained for weakly-anchored MBBA layers [12] while the threshold voltages, higher for thinner cells and lower for thicker cells, w r ere very different from those measured for weakly-anchored MBBA layers (Figs. 2 and 3) [12].…”

“…Longitudinal surface-induced flexoelectric domains created in weakly-anchored nematics with small dielectric anisotropy were recently investigated by us [11], [12]. The weak surface anchoring tions of the isotropic [13], electrohydrodynamic [14], [15], [16] and flexoelectric mechanisms are discussed in detail.…”

Crossover Between Flexoelectric Stripe Patterns and Electroconvection in Hybrid Aligned Nematics

“…In particular, the flexoelectric instability in planarly aligned nematics leads to a static periodic deformations of the director in the form of longitudinal domains [3,4,5].…”