Electrically induced anchoring transition in nematics with small or zero dielectric anisotropy

Abstract

Electrically induced anchoring transition in nematics with small or zero dielectric anisotropy The orientational transitions induced by electrically controlled ionic modification of surface anchoring in liquid crystal cells based on the nematics with small or zero dielectric anisotropy Δε are considered. The type of director reorientation is shown to be independent of the sign of dielectric anisotropy and can be the same for the nematics with both negative and positive Δε. Besides, the orientational transition and corresponding switchable optical states do not depend on the Δε value and can be effectively realized even for the nematics with zero dielectric anisotropy.

Orientational instability of the director in a nematic cell caused by electro-induced anchoring modification

“…At a sufficient surface density, these adsorbed ions can orient NLC molecules homeotropically in the layer adjacent to the surface, using their long elastic tails, independently of the way NLC molecules were oriented in the absence of adsorption. This mechanism was used in a number of experiments [14][15][16][17][18], where, owing to adsorption/desorption phenomena, the possibility to dynamically control the anchoring parameters using an electric field was demonstrated. In particular, the authors of [14,17] studied the dynamics of orientational transitions from the homeotropic NLC director configuration to the homeotropic-planar configuration and vice versa after the field was turned on and subsequently turned off.…”

Synthesis of Organotriphenylphosphonium Halides, Quaternary Ammonium Salts and Study of their Application as Surfactants Soluble in Liquid Crystals

“…Недавно нами был разработан новый метод управления ЖК-материалами, основанный на модификации поверхностного сцепления ионным сурфактантом при воздействии постоянного электрического поля, который успешно применен как для капельных дисперсий нематиков и холестериков в полимерах (капсулированных полимером жидких кристаллов -КПЖК) [4][5][6][7][8][9][10], так и для электрооптических ячеек, содержащих слой ЖК [11][12][13][14][15][16]. В качестве ионного сурфактанта использовался ЦТАБ, поверхностно-активные катионы которого ЦТА + , перемещаясь под действием электрического поля, формируют на поверхности подложек гомеотропно ориентирующие слои, либо, наоборот, происходит деструкция таких слоев.…”

Anionic-cationic surfactant mixture providing the electrically controlled homeotropic surface anchoring of liquid crystals

“…Using of ionic surfactants allows modifying the orienting influence of definite interface area due to the applied voltage which changes the ion concentration at the corresponding part of droplets [19][20][21][22] or on the substrate of flat LC cells [23][24][25]. Such anchoring transitions cause the transformation of orientational structures which cannot be obtained by using the Frederiks effect [26,27]. This approach to control a director configuration is known as the ionic-surfactant method [19][20][21][22][23][24][25][26][27].…”

“…Such anchoring transitions cause the transformation of orientational structures which cannot be obtained by using the Frederiks effect [26,27]. This approach to control a director configuration is known as the ionic-surfactant method [19][20][21][22][23][24][25][26][27]. The method was realized previously only with cationic surfactant cetyltrimethylammonium bromide (CTAB), that limits the application of this method, since the modification of boundary conditions occurs only near one of the electrodes.…”