Recent advances in thermotropic liquid crystals

Abstract

Liquid crystals are states of condensed matter whose symmetries lie between those of 3-dimensionally peri-odic crystals and isotropic liquids. Thermotropic liquid crystalline phases are exhibited by a large number of organic compounds whose molecules have anisotropy of shape. A typical intermolecular energy responsible for the stability of the relevant order in the medium is comparable to the thermal energy, and thus liquid crystals are soft materials. Relatively weak interactions like those between molecular dipoles or chiral centers of appropriate molecules can give rise to new types of liquid crystals. Now more than 35 types are known, and many more are likely to be discovered in the future. The soft nature of the medium, coupled with anisotropic optical and dielectric properties gives rise to many electro-optic effects at relatively low voltages. These are exploited in liquid crystal displays (LCDs), which are the lowest power (~ 1 µw/cm²) consuming flat panel devices and used in all calculators, laptop and palmtop computers, cell-phones, etc. Further, phase transitions between different types of liquid crystals, some of which are analogous to those in other materials like magnets or superconductors, offer a rich variety of problems of fundamental significance. As such, the R&D effort on liquid crystals has been growing steadily in the past three decades, resulting in better and cheaper displays as well as discoveries of new types of liquid crystals. The article gives a broad overview of the subject.