Microsphere manipulation using ferroelectric liquid crystals

We propose a strategy for a micromanipulation method using SSFLC (surface stabilized ferroelectric liquid crystals). By adjusting the frequency of the applied ac electric field, the surface layers that cannot follow an applied ac electric field are constructed in SSFLC. In addition, by applying a sawtooth wave voltage, net flow along the smectic layer is generated. The flow direction is reversed by changing the polarity of the sawtooth wave. Consequently, the particles dispersed in SSFLC can be driven bidirectionally along the smectic layer. The particle velocity depends on the temperature, amplitude, and frequency of the applied voltage.     

Photorefractive effect in ferroelectric liquid crystals

In this paper, we review recent progress of research on the photorefractive effect of ferroelectric liquid crystals. The photorefractive effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical photorefractive materials. A refractive index grating formation time of 8–10 ms and a large gain coefficient are easily obtained in photorefractive ferroelectric liquid crystals.     

Phase transitions in ferroelectric liquid crystals

Molecular chirality plays an important role in the science of liquid crystals, leading to cholesteric liquid crystal, blue phases, ferroelectric and antiferroelectric smectic phases and twist grain boundary phases. In all of these mesogens, chirality is an intrinsic property built into the chemical structure of mesogenic molecules. The study of ferroelectric liquid crystals has seen substantial experimental strides. In theoretical aspects, there has been relatively little basic work on this fascinating class of material. This review will try to present a comprehensive overview of the current status of the phase transitions in ferroelectric smectic liquid crystals. The article begins with a brief introduction about the symmetry and structure of ferroelectric mesophases. An attempt is made to identify a range of problems and related questions associated with the study of phase transitions. In the remaining parts of the article the important experimental and theoretical developments are summarized. Finally, some of the future directions have been identified.     

Echo response in ferroelectric liquid crystals

It is proposed that the kinetics and dynamics of ferroelectric liquid crystals may be studied by using the echo responses to the pulsed action of a microwave electric field. For ferroelectric liquid crystals, with homogeneously oriented molecules, calculations are made of the echo signals for two pulses and it is shown that these have values which are quite easily measured. Fiz. Tverd. Tela (St. Petersburg) 40, 1370–1372 (July 1998)     

Long-range interlayer interactions in ferroelectric liquid crystals

Some smectic liquid crystals exhibit a series of phases, including ferroelectric, antiferroelectric, and ferrielectric commensurate structures as well as an incommensurate phase. A long-standing problem has been to understand the origin of the long-range interaction responsible for this rich variety of phases. We study a model that incorporates thermal fluctuations in the flexing of layers and find that it supports commensurate and incommensurate structures. The vibrational entropy competes with an assumed helical interaction between nearest-neighbor layers. An increase in temperature then leads to an unwinding of the helix that proceeds at first through commensurate phases and then into an incommensurate phase. This result is consistent with the experimentally observed "distorted clock model."     

Nonlinear optical ferroelectric liquid crystals and device configurations

Ferroelectric Liquid Crystals (FLCs) are presented which comprise charge-transfer functional groups, such that highly efficient NonLinear Optical (NLO) properties and pronounced ferroelectricity result. By operating the NLO-FLCs in one of the two Bistable states of the Short-pitch Ferroelectric (SPF) conformation, stable, planar waveguides result. The NLO-FLCs exhibit exceptionally large second-order NLO-coefficientsd ₂₂ = 5 pm/V. Moreover, their linear electrooptical effect is shown to be essentially electronic in nature. This renders ultrafast electrooptical modulators with NLO-FLCs feasible.     

Holographic diffraction gratings using polymer-dispersed ferroelectric liquid crystals

By controlling the morphology of holographic polymer-dispersed ferroelectric liquid crystals (FLCs), highly aligned FLC domains are obtained for diffractive optical applications. Rapid, thresholdless switching is observed for various grating pitch sizes between approximately 3 and approximately 12 microm. A simple phenomenological model is presented encompassing a distribution of domain sizes and an effective field that stabilizes the FLC domains to reflect the observed thresholdless switching and optical behavior.     

Molecular relaxation in homeotropically aligned ferroelectric liquid crystals

Uniform and defect-free homeotropic (HMT) alignment of ferroelectric liquid crystals (FLC) cells have been successfully achieved by a non-contact technique, namely, magnetic field-assisted alignment; otherwise such alignment is difficult by conventional methods. Frequency-temperature dependent dielectric studies, confirm the presence of stable molecular relaxation around the short axis of FLC molecule, throughout SmC*-SmA* phases with minimum low-frequency fluctuations, known as Goldstone modes. The proposed non-contact alignment method, combined with FLC-based HMT configuration, would be much promising for integrated-optoelectronic devices, such as micro-mirror displays.     

Effect of dichroic azo-dye doped on ferroelectric liquid crystals

In order to study the effect of mixing dye in ferroelectric liquid crystal （FLC） materials, the phase transition temperature and electro-optical properties of azo dye doped FLC samples have been investigated. All the properties have been found to be changed drastically. The results have revealed that not only the SmC^＊- SmA^＊ transition temperature decreased markedly by the addition of azo-dye, but also dye-doped FLC had lower threshold voltage and saturation voltage than the pure FLC.     

Interface dynamics in liquid crystals

We have experimentally observed the pattern instabilities of an Ising wall formed in a nematic or cholesteric liquid crystal layer. We have deduced an envelope equation, relevant close to the Fréedericksz transition, from which we derived an equation for the dynamics of the interface in the vicinity of its bifurcation. In the case of the zig-zag instability, this model is characterized by a conservative and variational order parameter whose gradient satisfies a Cahn-Hilliard equation. We have also investigated the influence of slightly broken symmetries on the dynamical behaviour of the system. The disappearance of the interface translational invariance or of the reflection symmetry along the wall axis may induce new interfacial patterns which have been both experimentally and theoretically pointed out. Received 5 August 1999 and Received in final form 13 September 1999     

Isotropic to ferroelectric and antiferroelectric liquid crystals phase transitions

This review is an attempt towards a unified picture of the direct transitions from the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases formed by rod-like and bent-core molecules. The Landau–Ginzburg theories of the phase transitions between the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases in compounds composed of chiral rod-like molecules and achiral bent-core molecules are presented. This includes a discussion of the nature of the order parameters and the nature of the various types of phase transitions. The various predictions are compared with the available experimental results.     

Surface effects and defect structures in ferroelectric liquid crystals

Summary The influence of boundaries on the smectic structure dielectric properties and polarization reversal processes in thin films of ferroelectric liquid crystals are discussed. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30-October 2, 1987.     

Optical model of transient light scattering in ferroelectric liquid crystals

A static optical model is developed for the effect of field-induced transient scattering on coherent light transmission through ferroelectric liquid crystals. Scattering processes are described by introducing an optically anisotropic medium containing scatterers (transient domains). The results presented in the paper are obtained for a plane parallel layer of ferroelectric liquid crystals with a planar helicoidal structure under normal illumination with a linearly polarized plane wave. An analysis is presented of the coherent transmittance of the layer in static applied electric fields.     

Control of molecular orientation in electrostatically stabilized ferroelectric liquid crystals

The continuously reorientable (XY-like) ferroelectric polarization density of a chiral smectic liquid crystal is shown experimentally to produce nearly complete screening of the applied electric field in an appropriate cell geometry. This screening, combined with the expulsion of polarization charge for large polarization materials, is shown to produce electrostatic control of the orientation of a uniform optic axis or polarization field.     

Orientational dynamics in nematic liquid crystals

We examine the behaviour of single-particle orientational time correlation functions in nematic liquid crystals. As well as the expected dynamics involving oscillation in a mean-field potential, and occasional jumps between orientations parallel and antiparallel to the director, we provide the first simulation evidence of long-time tails characteristic of coupling to director fluctuations.     

Electrical Freedericksz transitions in nematic liquid crystals containing ferroelectric nanoparticles

A new theoretical approach was elaborated to explain the contradictions reported in many papers about the electric threshold for Freedericksz transition in nematic liquid crystal (NLC) with ferroparticles additives. The free energy density of the mixture was estimated and the contributions of the interaction energy of NLC molecules with ferroparticles surface were calculated. Experimental results for 5CB-BaTiO₃ mixture are given.     

New nonlinear optical processes in liquid crystals

We have worked out some consequences of the optical nonlinearities due to laser induced changes in the order parameter of a liquid crystal. The change in the order parameter can be affected by laser induced suppression of the director fluctuations in liquid crystals and or changes in the tilt angle of smectic liquid crystals. Both the processes lead to well known nonlinear optical effects like self-focusing, self-divergence, self-phase modulation, wave mixing, and so on. In addition, we predict some new phenomena like self-iridescence and new types of optical spatial solitons. In the case of chiral liquid crystals in the short wavelength limit the laser beam induces a change in the twist and at the long wavelength edge of the Bragg band it leads to temporal oscillations in the twist and the transmitted intensity. In smectic liquid crystals interesting periodic structures in a standing laser wave are to be expected.