Polymer Liquid Crystals

Abstract

The field of polymer liquid crystals is encompassing an increasingly wide range of research areas and applications, as was demonstrated at a recent one day meeting devoted to the subject. The meeting was held in London at the Scientific Societies Lecture Theatre, and was organized by the Institute of Physics Polymer Physics Group and co-sponsored by the British Liquid Crystal Society and the Royal Society of Chemistry.     

Liquid Crystals Tomorrow

Abstract

This issue of Liquid Crystals Today is slimmer than usual, and so provides an excuse for an editorial. Copy for Liquid Crystals Today comes through a variety of channels: some items are sent unsolicited to the editor or members of the editorial board, while feature articles are often written as a result of one of the editorial team reading or hearing about some new development in liquid crystal science. The flow of contributions is, therefore, random, and one of the tasks of the editor is to try to ensure that, from this random flow, a steady stream of high quality material emerges to coincide with the publication dates. This time it hasn't happened, so rather than wait for articles in the pipe-line, we have decided to publish a thin edition of Liquid Crystals Today. We do have some excellent articles being prepared, and we expect to publish an extended edition next time to include these.     

Carbohydrate Liquid Crystals

Certain alkyl l-O and l-S glycosides with hydrocarbon chain lengths greater than hexyl have been shown to form thermotropic liquid crystals at temperatures between 60 and 100[ddot]C. These are believed to be members of a large class of alkyl and acyl carbohydrate mesogens which, apart from their intrinsic value as potentially useful solid-state materials, could provide a variety of structurally accessible model systems for studying the phase transitions in the cell-membrane glycolipids.     

Ferroelectric Liquid Crystals

A review of the ferroelectricity in liquid crystals is given, beginning with a discussion of the symmetry properties allowing a macroscopic polarization in some of the more ordered liquid crystal phases. The fundamental mechanisms behind the dipolar ordering are discussed in some detail. The two linear electric effects, ferro- and flexo-electricity, give rise to completely different phenomena. In the smectic C phase there is one ferroelectric coefficient and nine flexoelectric ones, giving independent contributions to the polarization of the medium. We further discuss helical and non-helical structures, doped and intrinsic infinite-pitch ferroelectrics and, finally, the rich potential of liquid crystal ferroelectrics aligned in the »book-shelfgeometry» for fast electro-optic devices.     

Nomenclature of Liquid Crystals

Abstract

One of the signs of the maturing of a new area of knowledge is a heightened discussion and awareness of nomenclature, conventions and labels. In emerging sciences, the facts are often in dispute or open to different interpretations, and so premature attempts to categorize and standardize will only serve to confuse and delay real understanding. Liquid crystal science is now of an age when the attention of its practitioners is being drawn to considerations of nomen-clature. Indeed in 1997 IUPAC (International Union of Pure and Applied Chemistry) issued provisional recommendations concerning the definition of basic terms and symbols for liquid crystals. Members of the International Liquid Crystals Society have become involved with the preparation of a final document, which hopefully will be generally accepted and followed by scientists in the field. Some of the initial recommendations have already been reported in the new Handbook of Liquid Cryrstals, published in 1998 [1], so the process of formalising the nomenclature of liquid crystals has begun.     

Liquid Crystals in Education

Abstract

The advancement of liquid crystal science and technology has been a truly interdisciplinary effort which combines basic principles of physics, chemistry, and engineering. The success of liquid crystal materials in flat panel displays and electro-optic applications can be attributed to the collaborations of scientists in various fields and the unique interface between academia and industry. Many scientists and engineers engaged in liquid crystal research are also educators in their respective disciplines andlor area of expertise. Those in academia routinely teach undergraduate and graduate courses in physics, chemistry, and engineering, and those in industry often find themselves teaching technical short courses and seminars. Many of us have visited elementary and high schools in the USA to speak to students about careers in science and engineering, and to present some eye-catching demonstrations that excite students about science and technology.     

Liquid Crystals of Disc-like Molecules

The paper deals with thermotropic mesomorphism in pure compounds composed of disc-like molecules. The disc-like mesogens known to date are reviewed and the present state of knowledge of the structures of the mesophases are described. A few brief remarks are made about the physics of these new systems.     

X-Ray Diffraction by Liquid Crystals

Following a very brief historical review, x-ray diffraction by nematic and smectic liquid crystals is critically examined in terms of the data available and the structural models and molecular theories that have been proposed to explain it. Studiesof TBBA are used to illustrate some of the principal mesophases that have been distinguished. Other types of liquid crystals and their phase transitions are also briefly reviewed.

This analysis shows that careful experimental work is still needed to decide the kinds of models that best describe the various types of mesophases that have been shown to exist.     

Self-Diffusion in Uniaxial Liquid Crystals

Expressions are given for the translational diffusion parameters of non-spherical solutes in nematic and smectic-A phases, as measured by magnetic field gradient spin-echo NMR.     

European Conference on Liquid Crystals

Abstract

From 5 to 10 March, 1995 the European Conference on Liquid Crystals (ECLC95) was held in Bovec, Slovenia. The Conference was organized by the liquid crystal group at the J. Stefan Institute and Department of Physics of the University of Ljubljana, with Martin copit as chairman and lgor Mujevit as scientific secretary. The Conference was the third in the series of the European Liquid Crystal Conferences; the others were held in Courmayeur, Italy in 1991, and in Flims, Switzerland in 1993. These biennial conferences continue the tradition of the European Winter Conferences and provide an international forum to enhance the exchange of scientific ideas and technological advances in the field of thermotropic and lyotropic liquid crystals and their applications.