Alan W. Hall

Transmission and amplification of information and properties in nanostructured liquid crystals.

In recent years the design of chemical structures of liquid-crystalline materials has developed rapidly, and in many cases changed radically. Since Reinitzers days, liquid crystals have either been classed as rodlike or disclike, with combinations of the two leading to phasmidic liquid crystals. The discovery that materials with bent molecular structures exhibited whole new families of mesophases inspired investigations into the liquid-crystal properties of materials with widely varying molecular topologies-from pyramids to crosses to dendritic molecules. As a result of conformational change, supermolecular materials can have deformable molecular structures, which can stabilize mesophase formation, and some materials that are non-mesogenic, on complexation form supramolecular liquid crystals. The formation of mesophases by individual molecular systems is a process of self-organization, whereas the mesophases of supramolecular systems are formed by self-assembly and self-organization. Herein we show 1) deformable molecular shapes and topologies of supermolecular and self-assembled supramolecular systems; 2) surface recognition processes of superstructures; and 3) that the transmission of those structures and their amplification can lead to unusual mesomorphic behavior where conventional continuum theory is not suitable for their description.

Effect of terminal functional group size on ferroelectric and antiferroelectric properties of liquid crystals

Through the incorporation of sterically hindering, bulky terminal groups into the structures of chiral and racemic smectic liquid‐crystalline materials, we sought to interfere with, and decouple, the layers of various mesophases. By varying the size of the terminal group we found that we could control the mesophase structure, and to some degree its physical properties. In this article we present textural and X‐ray data which give insights into the structures of the mesophases.

Unsymmetrical alkoxy-substituted triphenylenes: the dependence of mesomorphism on molecular shape

Several series of unsymmetrical hexa-alkoxytriphenylenes have been prepared. For almost every series a maximum in the Colh-I clearing point is found for the most symmetrical triphenylene, i.e. when all six alkoxy chains are of equal length. A similar trend is found for the melting points (Tm), although the effect is not so pronounced. A minimum length is required for formation of a columnar mesophase (Col hd). After this critical value has been reached for short alkoxy chains, much lower Colh-I temperatures are then observed for longer chains. Ordered hexagonal columnar phases required for efficient photoluminescence and electroluminescence have been found for several asymmetrical homologues with comparable TCol-I to those observed for the symmetrical homologues, but also with lower Tm. This may facilitate the preparation of mixtures of triphenylenes with the desired ordered hexagonal columnar phases with a TCol-I and a Tm below room temperature.

Dielectric spectroscopy of the twist grain boundary phase and smectic‐like behaviour in the Isotropic Phase

Dielectric properties of a novel liquid crystal with direct transition from isotropic to twist grain boundary (TGB) phase were studied. Measurements were performed over a wide range of temperature in the isotropic phase, TGBA, TGBC and SmC* phases. The Arrhenius plot of the relaxation frequency of the molecular process around the short axis shows a variation in the activation energy in the isotropic phase. This is attributed to smectic‐like fluctuations in the isotropic phase. The dielectric relaxation strength in the TGBC phase has anomalous behaviour in the vicinity of TGBC–SmC* transition. The single cellective process observed in the TGBC phase splits into two processes in the SmC* phase.

Synthesis and Molecular Properties of New Side-Chain Liquid Crystalline Polymers Based on the Baylis-Hillman Reaction

Abstract A new methodology has been employed in synthesis of two side-chain liquid-crystalline polymers with cyanobiphenylene mesogenic groups and variation of -CN, -COCH3 and -OH groups displacement in the backbone surrounding. Hydrodynamic and electrooptical (the Kerr effect) methods were used to study their molecular properties in solution in benzene and chloroform. Electrooptical properties of polymers are compared with the same ones of homologous series of alkoxycyanobiphenylenes as the model compounds of the polymer mesogenic groups. Different mobility of the side-chain mesogenic groups in polymers under investigation was observed and related to the chemical and dipole structure.

Fluorocarbon and hydrocarbon end groups: effects on mesomorphism and physical properties of smectic liquid crystals

In this article we examine the effects of cyclohexane and perfluorocyclohexane being used as bulky end groups on the mesomorphism of classical smectic liquid crystal mesogens. The mesogen that is used in this work is typical of the MHPOBC family of materials. The mesophase behaviour is investigated and miscibility studies are carried out. Electro-optical evaluation of the materials is investigated to show the effect of the terminal group on physical properties such as spontaneous polarisation and tilt angle.

A chiral electrooptic response in a racemic liquid crystal

Over recent years, little attention has been paid to the electrooptic properties of racemic modifications of smectic liquid crystals, however, in this communication we report on a chiral response of a racemic modification to an applied electrical field while in its synclinic smectic C phase.

The photoinitiated cyclopolymerization of dienes in the creation of novel polymeric systems and three-dimensional networks

In this article we describe the photo-initiated cyclopolymerization of 5-, 6- and 7-centre dienes. We find that substituted dienes can be cyclopolymerized in sunlight or by the use of a low-power UVA sunlamp of broad spectral range (320–400 nm). Unless activated by suitable electron withdrawing groups the cyclopolymerization can often be slow and incomplete. However, when suitably activated the polymerization rates can approach those for acrylates. In particular diallylamine, its quaternary salts, which can often be obtained as ionic fluids, and diallylamide, can be subjected to fairly rapid photocyclopolymerization to give robust coatings and adhesives. This discovery augments, and gives a different dimension, to the acrylate and methacrylate monomer and polymer systems that are already commercially available.

Novel UV cured coatings and adhesives based on the photoinitiated cyclopolymerization of derivatives of diallylamine

A new family of non-acrylate UV cured three-dimensional polymeric networks for coatings and adhesives based on the photoinitiated cyclopolymerization of diallylamine salts and diallylamides using a low power (75 W) UVA domestic sunlamp is described.

Optical waveguide characterization of a tristable antiferroelectric liquid crystal cell

The optical convergent-beam waveguide technique has been used to characterize a homogeneously aligned 3 μm cell containing a liquid crystal in the antiferroelectric phase. The director structure has been quantified with the cell at 0 V and at ±50 V dc, and three distinct states have been observed. From the optical data collected, it is found that the material forms a tilted-bookshelf ferroelectric structure in the presence of a suitable voltage, and the characteristic alternating (anticlinic) structure of the antiferroelectric phase when the cell is short-circuited. The biaxiality of the antiferroelectric state has been measured, and (approximately) uniaxial refractive indices, the cone angle, and layer tilt have been determined for the ferroelectric state.