Nematic liquid crystal devices with sub-millisecond response time

Conventional nematic liquid crystal devices exhibit switching times that are in the order of several milliseconds. In this work we focus on two types of nematic liquid crystals that can overcome the limitations of conventional nematic liquid crystals and allow sub-millisecond switching times for both switching on and off: nano-pore polymer-liquid crystals and dual-frequency liquid crystals

Fourth order nematic elasticity and modulated nematic phases: a poor man's approach

We propose an extension of Frank-Oseen's elastic energy for bulk nematic liquid crystals which is based on the hypothesis that the fundamental deformations allowed in nematic liquid crystals are splay, twist and bend. The extended elastic energy is a fourth order form in the fundamental deformations. The existence of bulk spontaneous modulated or deformed nematic liquid crystal ground states is investigated. The analysis is limited to bulk nematic liquid crystals in the absence of limiting surfaces and/or external fields. The non deformed ground state is stable only when Frank-Oseen's elastic constants are positive. In case where at least one of them is negative, the ground state becomes deformed. The analysis of the stability of the deformed states in the space of the elastic parameters allows to characterize different types of deformed nematic phases. Some of them are new nematic phases, for instance a twist -- splay nematic phase is predicted. Inequalities between second order elastic constants which govern the stability of the twist--bend and splay--bend state are obtained

Theory and simulation of the nematic zenithal anchoring coefficient

Combining molecular simulation, Onsager theory and the elastic description of nematic liquid crystals, we study the dependence of the nematic liquid crystal elastic constants and the zenithal surface anchoring coefficient on the value of the bulk order parameter

Observation of lyotropic chromonic liquid crystals droplets with the perpendicular boundary condition

Department of PhysicsControlling anchoring conditions of liquid crystals (LCs) is crucial for the study of liquid crystals and development of liquid crystals-based displays and sensors. Although many studies have been made on thermotropic liquid crystals, the anchoring conditions of lyotropic chromonic liquid crystals (LCLCs) are difficult to control even through properties of LCLCs were actively studied. Conventional alignment methods have no effect on LCLCs, even work, anchoring is very weak. Only a few perpendicular alignment layers (a.k.a. homeotropic anchoring) in solid-LCs interfaces were reported through non-covalent interactions of hydrophobic polymer films and solid substrates such as graphene. However, the vertical alignment layers of LCLCs at the liquid interface has never been reported. We report, for the first time, the study of the homeotropic anchoring of liquid and LCLCs interfaces using hydrophobic oils without surfactants. As reported in thermotropic liquid crystals, a radial structure with a point defect has been found, but an unusual feature is the axial structure with ring disclination, which did not apply the external field. It implies that this anchoring strength is very weak anchoring conditions and another supporting evidence is the anchoring transition, which changes to the horizontal orientation from the perpendicular orientation. Also, because of the weak twist modulus of the LCLCs, the structure of the defects seemed to be twisted. This twist structure is consistent with previous reports. To observe the structures of homeotropic chiral nematic, brucine sulfate was used as a chiral dopants. Basically, we reproduced the director configurations of the droplets of the thermotropic chiral nematic LCs both with planar and homeotropic anchoring. Specifically, with the homeotropic anchoring, we noticed an increase in the effective helical pitch in the droplets according to the droplet size, i.e. the untwisting of the helical structure, which originates from the frustration of chiral nematic liquid crystals with the perpendicular boundary condition.ope

Nematic liquid crystals for optical shutters: A concept

Nonmechanical shutter utilizes nematic crystals to attenuate illumination, thus protecting light-sensitive devices such as vidicon or image orthicon tubes and phototubes. Opacity of liquid crystals is controlled by photosensor