Antiferroelectric and ferroelectric switching of a liquid crystal in Langmuir-Blodgett films under strong confinement conditions

An antiferroelectric liquid-crystal (LC) material formed of banana-shaped molecules in the sandwich metal-thin Langmuir-Blodgett film-metal geometry, which is typical of solid-state technology, is investigated. Upon heating the thin-film elements, the material passes to the high-temperature (68–127°C) LC B ₂ phase, which, despite severe limitation on the film thickness (∼100 nm or less), exhibits antiferroelectric switching, which was previously observed only in bulk samples (10 μm thick) of the LC studied. At film thicknesses smaller than ∼40 nm, ferroelectric switching is observed, which is caused by the stabilization of the ferroelectric LC phase by the boundary surfaces. The largest values of the switched polarization of films (∼400 nC/cm²) are comparable with the polarization of bulk samples. The coercive field increases with decreasing film thickness and reaches ∼10⁶ V/cm for the thinnest films. This value corresponds to the intrinsic coercive field of the ferroelectric under conditions of a strong surface effect, which suppresses domain processes. Published in Russian in Kristallografiya, 2006, Vol. 51, No. 5, pp. 898–905. Dedicated to the 60th Birthday of M.V. Kovalchuk The text was submitted by the authors in English.     

Bistable and multistable states in ferroelectric liquid crystals

The effect of memorizing the structural states in a ferroelectric liquid crystal (FLC), known as biand multistability, is based on the existence of a domain structure that changes its properties under the action of an applied voltage. The criterion for the bistability steadiness of the optical-transmission states of FLC electrooptic cells is developed. This criterion is related to the hysteresis-loop parameters of the FLC layer. The conditions for the existence and steadiness of the hysteresis-free switching of the memorized optical-transmission states of multistable electrooptic cells are formulated.     

Modal liquid crystal lenses

Abstract

When considering the possibility of commercially viable applications for discotic liquid crystals it is worth noting that in the case of calamitic liquid crystals some 80 to 90 years elapsed between their discovery in 1888 and their first application in displays. Since discotic mesophases were only discovered in 1977 [ll, it is not surprising that the first applications are yet to be realized.     

Soliton excitations in liquid crystal polyacetylene

Abstract

A disubstituted polyacetylene with lyotropic liquid crystallinity showing SmA was synthesized. The number-average-molecular weight of the polymer was 5.2?×?10⁵ g/mol. Vapor phase iodine doping for the disubstituted polyacetylene in the form of liquid crystal order allows the generation of charge carriers. The ESR measurements show the charge carriers exhibit Pauli paramagnetism, indicating that these carriers are polarons. Mott-type variable range hopping (VRH) conduction of the polymer was observed. The combination of SmA molecular architecture and electrical conduction by polyene as a molecular wire in the polyacetylene derivative results in liquid crystal electrical conduction via electro-soliton movement.     

Modification in dielectric properties of SWCNT doped ferroelectric liquid crystals

Effect of single walled carbon nanotubes (SWCNT) in ferroelectric liquid crystal (FLC) geometry has been studied for low and high concentrations of dopant. The results are compared with the characteristics of pure FLC system. An appreciable change in dielectric permittivity, relaxation behavior and other vital parameters has been observed for SWCNT doped FLC system, which shows the adaptability of carbon nanotubes with that of pure FLC molecule. Under high electric field, highly concentrated SWCNT doped FLC shows enormously large values of dielectric loss. This is due to the high conductivity of SWCNT at higher electric field. Interestingly, such effect is not much prominent for the low concentration of the SWCNT doped FLC system.     

Problems in crystal chemistry of ferroelectric and antiferroelectric perovskites PbB

The most interesting problems in the crystal chemistry of ferroelectric and antiferroelectric perovskites PbB _0.5 ^′ B _0.5 ^″ O₃ are considered. The properties and specific features of perovskites (such as the smearing of ferroelectric phase transitions, relaxor state, ferroelectric-antiferroelectric transformations, and spontaneous phase transitions to a macrodomain state) depend on the distribution of B′ and B″ ions over octahedral positions of the crystal lattice, i.e., on the order and disorder of these ions. __________ Translated from Kristallografiya, Vol. 49, No. 5, 2004, pp. 806–810. Original Russian Text Copyright ? 2004 by Isupov.     

Advanced electro-optic properties of nematic liquid crystal doped with high birefringence liquid crystal molecules

The study of fast response nematic liquid crystal display material mixture and synthesis about compounds has always been an important subject in recent years. In this article, one type of high birefringence liquid crystal based on phenyl-diacetylenes was synthesized by sonogashira coupling reaction. A research is conducted on the effect of electro-optic properties of a widely used nematic liquid crystal mixture doped with the prepared high birefringence liquid crystal molecule which concentrations ranging from 1% to 5 wt%. While the results show that the steepness of electro-optic curves first increase and then decrease with the prepared high birefringence liquid crystal molecule content increasing, when the content of high birefringence liquid crystal molecule reaches 3%, electro-optic properties of the mixture liquid crystals are excellent.     

A review of radial segregation in crystal growth during microgravity

This review describes radial segregation results from crystal growth experiments in microgravity, together with their corresponding theoretical treatments. The paper is structured in terms of the different factors influencing radial segregation during crystal growth, such as: curved growth interfaces, variations in boundary layer thickness, weak convection, facets and magnetic fields.In a number of experiments considerably stronger radial segregation occurs in space than is normally observed on earth. The theoretical treatments lead to a sound understanding of all of the results. Possible ways to avoid the problem, such as the application of magnetic fields, are outlined.     

Porous glass-ceramics composed of a titanium phosphate crystal skeleton: A review

Bulk microporous glass-ceramics with a skeleton of two types of functional titanium phosphate crystal were prepared by controlled crystallization of RTi₂(PO₄)₃ (

Full-size image

glasses, and chemical treatment. One crystal is a NASICON-type with a three-dimensional network structure of TiO₆ and PO₄ while the other is a zirconium phosphate-type crystal Ti(HPO₄)₂ · 2H₂O with a two-dimensional layered structure. The mean pore diameter and porosity of 30–60 nm and 40–60 vol.% were achieved. Porous CaTi₄(PO₄)₆ glass-ceramics have excellent properties as supports for immobilization of enzymes, humidity sensors and porous LiTi₂(PO₄)₃ glass-ceramics as ion exchange media. Conspicuous bacteriostatic activities were found for the partially Ag-exchanged porous LiTi₂(PO₄)₃ and Li_1.4Ti_1.6Al_0.4(PO₄)₃. Integrated microporous glass-ceramics with skeletons of LiTi₂(PO₄)₃ (LTP) and Ti(HPO₄)₂ · 2H₂O (TP) crystals were synthesized utilizing a novel discovery that LTP is transformed into TP in acid solution.     

Piezoelectricity in crystallizing ferroelectric polymers: Poly(vinylidene fluoride) and its copolymers (A review)

The piezoelectricity observed in poly(vinylidene fluoride) (PVDF) and its copolymers involves three components that are associated with the presence of at least two phases (crystalline and amorphous) in the polymer structure. The main contributions to the phenomenon observed are made by the size effect and electrostriction, which are related to each other. These contributions manifest themselves through the mechanism of strain-induced reversible transformations of a number of domains of the anisotropic amorphous phase into the crystalline state under the action of mechanical or electrical fields. With due regard for different packings of chains in the amorphous and crystalline phases, this mechanism accounts for the large Poisson ratios μ₃₁ obtained for textured films of flexible-chain crystallizing polymers. The dependence of the piezoelectric coefficient d ₃₂ on the static stress in textured films is governed by the change in the fraction of the crystalline phase due to strong anisotropy of the elastic constants in the film plane. It is shown that the shear deformations of polymers are characterized by a strong piezoelectric response. The specific features revealed in the piezoelectric effect under bending deformations are described for films with an inhomogeneous distribution of polarization over the cross section. The general regularities of the electrostriction in the polymers and inorganic relaxor ferroelectrics studied are considered.     

On the nature of the orientational effect of ultrasound on nematic liquid crystal

Experimental substantiation of the validity of the model of orientational distortion in a homeotropic layer of nematic liquid crystal under an ultrasonic beam with a sharp boundary is presented for the first time. The model is constructed within the concepts of nonequilibrium thermodynamics and statistical hydrodynamics, taking into account the processes of structural relaxation of the mesophase. It establishes the relationship between the characteristics specifying the homeotropic structure deformation (layer thickness, ultrasound frequency, parameters of the molecular micromodel of liquid crystal, and its material constants) and the layer transparency for a linearly polarized light beam. The calculation results are compared with the experimental data in the frequency range of 0.1–3 MHz.     

Periodic-shear-induced vortex structures in nematic liquid crystal

The effect of the periodic shear in the ultrasonic range on a homeotropically oriented layer in a nematic liquid crystal has been studied. The formation of a vortex lattice whose points are the centers of autowaves is established. The formation and stability of the vortex lattice are shown to be related to the processes of synchronization of spatial oscillators (autowave centers) and their interactions, as well as to the processes of self-organization.     

Simulation of electrooptical effects and dynamics of ferroelectric liquid crystals

The behavior of ferroelectric liquid crystals in an external electric field is simulated numerically. The equations that describe the dynamics of the director of a liquid crystal are derived within the continuum theory of elasticity with due regard for compressibility of smectic layers, finite anchoring energy, and dielectric properties of orienting coatings and external elements of a real electric circuit. These equations make the basis for simulation of the electrooptics of ferroelectric liquid crystals. The specific features and mechanisms of the surface-stabilized bistability and hysteresis-free electrooptical switching (the V-shape effect) are discussed.     

Ferroelectric liquid crystal over silicon devices

Over the past 20 years, ferroelectric liquid crystal over silicon (FLCOS) devices have made a wide impact on applications as diverse as optical correlation and holographic projection. To cover the entire gamut of this technology would be difficult and long winded; hence, this paper describes the significant developments of FLCOS within the Engineering Department at the University of Cambridge.

The purpose of this paper is to highlight the key issues in fabricating silicon backplane spatial light modulators (SLMs) and to indicate ways in which the technology can be fabricated using cheap, low-density production and manufacturability. Three main devices have been fabricated as part of several research programmes and are documented in this paper. The fast bitplane SLM and the reconfigurable optical switches for aerospace and telecommunications systems (ROSES) SLM will form the basis of a case study to outline the overall processes involved. There is a great deal of commonality in the fabrication processes for all three devices, which indicates their potential strength and demonstrates that these processes can be made independent of the SLMs that are being assembled. What is described is a generic process that can be applied to any silicon backplane SLM on a die-by-die basis. There are hundreds of factors that can affect the yield in a manufacturing process and the purpose of a good process design procedure is to minimise these factors. One of the most important features in designing a process is fabrication experience, as so many of the lessons in this business can only be learned this way. We are working with the advantage of knowing the mistakes already made in the flat panel display industry, but we are also faced with the fact that those mistakes took many years and many millions of dollars to make.

The fabrication process developed here originates and adapts earlier processes from various groups around the world. There are also a few totally new processes that have now been adopted by others in the field. Many, such as the gluing process, are still on-going and have to be worked on more before they will fully suit ‘manufacturability’.