Research on liquid crystals (LC) started in mid 18th century. In 1850 W. Heintz discovered that stearin (a biochemical compound) changed its optical properties when its temperature is raised. In 1888 Friedrich Reinitzer discovered the basic principle behind liquid crystals. Lehmann and others stated liquid crystals as a new phase of matter. In 1991, Pierre-Gilles de Gennes received the Nobel Prize in physics for designing simple systems to measure complex phenomenon, especially with respect to Liquid crystals.
Liquid Crystals in Living Organisms
Liquid crystals are present in biological systems and are part of important biological functions and units like DNA, cell membranes and polypeptides. Collagens and Dragline Silks (spider web) are some biological compounds that behave like liquid crystals. Lipids (one of the most common biological compounds) show liquid crystal properties near their melting temperature. Biological compounds form a separate class of materials: liquid crystal elastomers(LCEs).
The Phases of Liquid Crystals
There are generally three liquid crystal phases: metallotropic, lyotropic and thermotropic. The metallotropic phase has both the organic and the inorganic crystals. Transition liquid crystal material in the metallotropic phase depends on the temperature and the concentration and ratio of inorganic: organic crystals. Thermotropic and lyotropic phases consist of only organic crystals. In the case of lyotropic phase, transition depends on changes in the temperature and the concentration. In the case of thermotropic phase, transition depends only on changes in the temperature.
Anisotropy of Liquid Crystals
The properties of liquid crystals are dependent on the orientation of the molecules of the material. Properties of liquid crystals are dependent on the direction in which the force is applied. Due to this, when a liquid crystal compound is flown through two close plates, dendritic patterns are formed. Properties like surface tension, ratio of equilibrium structures and thermal conductivity also show this anisotropic behavior.
Theoretical Treatments of Liquid Crystals
Scientists have long tried to cover major aspects of phase transition in liquid crystals. Many factors play role in the complex interactions of the LC material. High material density, hardcore repulsions and multiple body correlations interact together to couple the orientation of the molecules with the force (impact). The direction of the orientation is defined by a vector called director.
- Order Parameter – Orientation order is an average of second Legendre polynomial.
- Onsager Hard-Rod Model – A prediction model to calculate lyotropic phase transitions.
- McMillan's Model – An extension to Maier-Saup mean field theory is used to predict the phase transition of LCs from a nematic to a smectic phase.
- Elastic Continuum Theory – In this theory molecules are considered to be oriented and changes in preferred orientations are measured as frank free energy density.
Liquid Crystal Applications
Liquid crystals find its application in liquid crystal displays, thermometers and semiconductor industry .They are also used as memory units in space shuttle equipments. They consume less electricity and hence provide better alternative to LCDs. New researches are targeted towards devising ultra-low energy utilizing LCD panels. Liquid crystals also find application in biotechnology (biosensors).
- Thermometer – Liquid crystals are used as materials to monitor temperature.
- Hot-Spots Identification – LCs are used in semiconductor industry to find electrically generated hot spots for failure analyses.
- LCD – Another application of LCs that can revolutionize the entertainment world.
- Display Working with LCs – This article gives a brief intro on devices and displays that use Liquid Crystals.
- Liquid Crystals – This link describes many applications of liquid crystals.
The discovery of liquid crystals has revolutionized the digital world. It has enhanced TV viewing experience for the masses. At the same time, it has made possible for mobiles to have a vibrant display. It has also lead to development of a new generation of laptops and tablets. LCs can be used in various applications. Its future lies in its application in energy-efficient displays and systems.