10.1 Overview

Many of us are familiar with liquid crystal displays on watches or electronic devices. We also may have seen mood rings and indicating thermometers. In addition, who among us has not seen the sludge like residue at the bottom of a soap dish? These all contain or are liquid crystal materials. Yet, we rarely think about the materials that make up the display, the thermometer, the ring, or the sludge. This chapter will introduce liquid crystals. We will answer the following questions:

1. What is a liquid crystal?

2. What types of molecules form liquid crystals?

3. What types of liquid crystals exist?

4. What phases of liquid crystals exist?

5. What are some properties of liquid crystals?

6. What are polymeric liquid crystals?

10.2 Liquid Crystals and Ordering

We now consider another extension of the common phases of matter which we discussed earlier solid, liquid, and gas. When certain organic materials (about one in 200) are heated, there is not a single phase transition from solid to liquid as is observed, for instance, in water. Instead, a cascade of phase transitions is observed involving phases with different mechanical and physical properties. Some of the physical properties of these new phases are intermediate between those of a crystalline solid and an isotropic liquid. For this reason, they are called liquid crystalline phases. A more accurate name is intermediate or mesomorphic phases.

To understand how these mesomorphic phases are both similar to and different from solids and liquids, it is useful to review...