Permeation in cholesteric liquid crystals

It is shown that permeation in cholesteric liquid crystals can be derived quite generally from Leslie's linearized equations for the conservation of linear and angular momentum.     

Permeative flows in cholesteric liquid crystals

We use lattice Boltzmann simulations to solve the Beris-Edwards equations of motion for a cholesteric liquid crystal subjected to Poiseuille flow along the direction of the helical axis (permeative flow). The results allow us to clarify and extend the approximate analytic treatments currently available. We find that if the cholesteric helix is pinned at the boundaries there is an enormous viscosity increase. If, instead, the helix is free the velocity profile is flattened, but the viscosity is essentially unchanged. We highlight the importance of secondary flows, and, for higher flow velocities, we identify a flow-induced double twist structure in the director field--reminiscent of the texture characteristic of blue phases.     

Ultraviolet lasing in cholesteric liquid crystals

We report the observation of stimulated emission and mirrorless lasing in pure cholesteric liquid crystals. The lasing action is attributed to the combination of the fluorescence and the distributed feedback that are due to the inherent periodic structure of the liquid crystal. If the reflection band matches the intrinsic emission of the cholesteric liquid crystal, the crystal becomes a natural laser material, which will self-lase, without any optical elements or the addition of dyes, under picosecond excitation at 355 nm. Samples have been made to lase at different wavelengths in the near UV by shifting of the edge of the reflection band in the range of 385-405 nm. Typical linewidths observed are of the order of 0.5 nm.     

Local-field anisotropy in cholesteric liquid crystals

The first experimental values of the Lorentz tensor components L _j for the cholesteric and smectic A phases of derivatives of cholesterol have been obtained using the dispersion of the refractive indices in the visible range. The temperature dependence of the components L _j has been determined; it is invariant with respect to the cholesteric-smectic A phase transition. The effect of the isotropization of the Lorentz and local field tensors with decreasing anisotropy of the molecular polarizability has been revealed.     

Density functional theory for chiral nematic liquid crystals

ABSTRACT

In this note, the density functional theory for chiral nematic liquid crystals is expressed in terms of rotational invariant expansion coefficients of the pair-excluded area at fixed separation. This modification from the standard approach, without making any additional assumptions, yields a more efficient procedure for minimising the free energy, as well as providing insight into the origins of the effect away from the long-pitch limit.     

Optical addressing in dye-doped cholesteric liquid crystals

This study investigates a method of optical addressing in dye-doped cholesteric liquid crystals (DDCLCs). Photo-induced randomly adsorbed dyes can change the CLC textures from planar to focal conic. Such patterning can be adopted to develop a display that is initially invisible, but becomes visible upon heating above the clearing temperature, followed by cooling to room temperature. The display can also become visible upon the application of a suitable voltage, and its rapid release. Additionally, the display is thermally erasable, optically rewritable and electrically switchable. It can be applied for use as a smart card.     

Reflection properties of distorted cholesteric liquid crystals

The optical reflection properties of distorted cholesteric liquid crystals are theoretically investigated. It is shown that higher-order reflection bands occur with distorted helical structures even for light propagation parallel to the twist axis. For aperiodic structures, the positions of the main reflection bands differ from that of periodic ones. Ferroelectric helical structures could be detected by reflection spectroscopy when the liquid crystal is deformed by an electric field.     

液晶胆甾相的形成机制

采用量子理论的方法研究了胆甾相液晶的形成机制.证明了通常采用的手性作用势确实能够导致胆甾相的形成，并给出螺距的表示式. 关键词： 液晶 量子理论 螺距     

Theory for cholesteric ordering in lyotropic liquid crystals

Summary This paper presents an investigation of the chiral dispersion interaction between macromolecules in the solvent which is considered as a dielectric medium. In particular the results of the molecular statistical theory are reported. The expression for the helical pitch as a function of temperature on the solvent dielectric constant is used to interpret the experimental data. Moreover, the effect of the solvent chirality on the cholesteric ordering in polymer liquid crystals is considered. Finally the cholesteric ordering in the solution of chiral micelles is discussed. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.     

Structures and thermoelectric convection in cholesteric liquid crystals

The possibilities for excitation of electromagnetic field structures and convection cells, i.e., temperature and velocity structures, in a thermotropic cholesteric liquid crystal in the presence of flow are studied. Estimates are made and possible experiments for observing such structures are discussed. A special thermoelectric effect is investigated as the cause of these excitations — the influence of a heating-induced change in the pitch of the cholesteric helix of the molecules on the permittivity and the electric conductivity of the material. Fiz. Tverd. Tela (St. Petersburg) 41, 165–170 (January 1999)     

Comments on thermomechanical coupling in cholesteric liquid crystals

The Onsager reciprocal relations give two more equalities between Leslie's coefficients. It suggests a simple experiment which could check Leslie's predictions.     

Mapping ultrasonic fields with cholesteric liquid crystals

The termperature-sensitive light-scattering properties of cholesteric liquid crystals have been applied to the mapping of the intensity distribution in the near-field of ultrasonic transducers.     

On the rotatory dispersion in cholesteric liquid crystals

It is shown that the dynamical theory of light propagation in a cholesteric liquid crystal does not predict a reversal in the sign of optical rotation on the long wavelength side of the reflection band. This conforms with the results of exact electromagnetic treatment.     

Electromechanical and light tunable cholesteric liquid crystals

A light-responsive cholesteric liquid crystal (CLC) mixture is tuned with light and applied DC electric field. Interestingly, the reflection of the CLC is red shifted with UV light and blue shifted with applied DC electric fields. UV light exposure induces a red shift in the reflection of the CLC bandgap by as much as 800 nm from the original spectral position. Spatial variations in pitch (and thus reflection color) are shown to blue shift with applied DC field regardless of the photohistory and restore the notch position or image upon removal of the field. The ability to tune the reflection of the CLC bandgap on demand to the red or blue with multiple stimuli is a never before demonstrated effect that could have potential utility in lasing, optical filtering, or data communication applications.