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

James Fergason, a Pioneer in Advancing of Liquid Crystal Technology

James Lee Fergason (1934 - 2008) focused his research on the liquid crystals. His studies correspond to a relevant part of the history of soft matter science and technology of liquid crystals. Here a discussion of some of his researches.Comment: Soft Matter, Liquid Crystals, Cholesterics, Nematics, Smectics, Liquid Crystal Display

Characterization and Biocompatibility Study of Nematic and Cholesteryl Liquid Crystals.

noIntensive research in bio-engineering has been conducted in the search for flexible biomaterials that could support cell growth and cells attachment. Flexible synthetic materials that support cell growth without the aid of synthetic extracellular matrix proteins are still rare. Cholesteryl liquid crystal containing cholesteryl moieties may have suitable biological affinity. Human keratinocytes (HaCat) were cultured with a nematic liquid crystal and three cholesteryl liquid crystals of different formulation. Subsequently, the trypan blue dye exclusion assay was used to determine cell viability in the liquid crystals. The two classes of liquid crystal were characterized by Differential Scanning Calorimeter (DSC) and polarizing microscope (POM) to understand the nature of the interface material. The cell viability study in medium containing liquid crystals verified that liquid crystals had no effects on cell viability. However, only the surface of cholesteryl liquid crystal has shown affinity to HaCat cells. In addition, cells continued to proliferate in the presence of liquid crystals without a change of medium for eight days. No sign of exothermic and endothermic activities at 370C were observed from the DSC test results for the three samples. Biological and mechanical test result of the cholesteryl liquid crystals has shown that cholesteryl liquid crystals are non toxic and support cell attachment without extracellular matrix protein at very low elasticity

Influence of anchoring in AFLC cells: Electro optical scanning

Antiferroelectric liquid crystals have gained a lot of interest in the last few years. In the case of ferroelectric liquid crystals, it is generally assumed that in a confined geometry the surface only has a minimal influence on the bulk when the thickness of the cell is much larger than the pitch of the helix. Some studies have shown that this rule doesn’t apply in the antiferroelectric liquid crystals case. In this contribution we study an antiferroelectric liquid crystal (MHPOBC) in a confined geometry by electro-optical scanning measurements

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

Living Liquid Crystals

Collective motion of self-propelled organisms or synthetic particles often termed active fluid has attracted enormous attention in broad scientific community because of it fundamentally non-equilibrium nature. Energy input and interactions among the moving units and the medium lead to complex dynamics. Here we introduce a new class of active matter, living liquid crystals (LLCs) that combine living swimming bacteria with a lyotropic liquid crystal. The physical properties of LLCs can be controlled by the amount of oxygen available to bacteria, by concentration of ingredients, or by temperature. Our studies reveal a wealth of new intriguing dynamic phenomena, caused by the coupling between the activity-triggered flow and long-range orientational order of the medium. Among these are (a) non-linear trajectories of bacterial motion guided by non-uniform director, (b) local melting of the liquid crystal caused by the bacteria-produced shear flows, (c) activity-triggered transition from a non-flowing uniform state into a flowing one-dimensional periodic pattern and its evolution into a turbulent array of topological defects, (d) birefringence-enabled visualization of microflow generated by the nanometers-thick bacterial flagella. Unlike their isotropic counterpart, the LLCs show collective dynamic effects at very low volume fraction of bacteria, on the order of 0.2%. Our work suggests an unorthodox design concept to control and manipulate the dynamic behavior of soft active matter and opens the door for potential biosensing and biomedical applications.Comment: 32 pages, 8 figures, Supporting Information include

Polar Molecular Organisation in Liquid Crystals

Various possibilities of polar self-organisation in low molar mass nematic, smectic and columnar liquid crystals are discussed with particular focus on the underlying molecular symmetries and interactions. Distinction is made between vector and pseudovector polarities, their quantification in terms of molecular order parameters and their relation to spontaneous electric polarisation and to molecular chirality. The understanding of the molecular mechanisms that give rise to polar ordering in existing lamellar and columnar phases may be useful for the design of new polar variants of common a-polar liquid crystals. Keywords:Polar Nematics; Ferroelectric Liquid Crystals; Polar Ordering.Comment: RevTex4, 10 pages, 8 figures, to be published in Mol. Cryst. Liq. Crys