1. Liquid crystal state

1.1 Definitions

Basic physics teaches us that matter exists in three states: solid, liquid or gas. This classification is in fact incomplete: many organic substances don't present a single change of state (or phase transition) between crystal and liquid, but a series of transitions giving rise to states whose physical properties are intermediate between crystal and liquid. These states, christened liquid crystals by Lehmann, are also known as mesomorphic (from the Greek: of intermediate form) or mesophase.

A crystal is characterized by a regular stacking of basic units (atoms, ions or molecules) on a periodic lattice in all three dimensions of space. The definition of the basic pattern (or mesh) is sufficient to determine the position of all the atoms, ions...