|Basic Scientific Description|
|A History of the Study of Liquid Crystals|
|Some images of liquid crystal textures|
Basic Scientific Description
Normally, we consider matter to have three distinct states: solid, liquid, and gas. However, there are states of matter which do not meet the necessary requirements of any of these three categories. For example, a substances such as mayonnaise is somewhere between a liquid and a solid.
Liquid crystals are also not quite liquid and not quite solid.
Physically, they are observed to flow like liquids, but they have
some properties of crystalline solids. Liquid crystals can be
considered to be crystals which have lost some or all of their
positional order, while maintaining full orientational order.
For example, imagine a large number of toothpicks put into a rectangular
box and shaken. When you open the box, the toothpicks will be
facing in about the same direction, but will have no definite
spatial organization. They are free to move, but like to line
up in about the same direction. This is a primitive model for
nematic liquid crystals.
|Nematic Liquid Crystals|
Nematics are polarizable rod-like organic
molecules on the order of 20 Angstroms in length. Because of their
tendency to organize themselves in a parallel fashion, they demonstrate
interesting and useful optical properties; the digital watch you
used to wear back in the 80's functioned using nematic liquid
crystals. Today, many more useful and interesting properties of
nematics are known and exploited.
|Smectic Liquid Crystals|
Smectic Liquid crystals are different from nematics in that they have one more degree of orientational order than do the nematics. Smectics generally form layers within which there is a loss of positional order, while orientational order is still preserved. There are several different categories to describe smectics. The two best known of these are Smectic A, in which the molecules align perpendicular to the layer planes, and Smectic C, where the alignment of the molecules is at some arbitrary angle to the normal.