Liquid crystals (LCs) are an important class of the soft matter systems with a distinctive feature of a long-range orientational order. Generally, molecular orientations in a liquid crystal cell form a complex 3D pattern.
In LCs the constituent molecules (or their aggregates) possess a long range orientational order but little or no positional order. LCs are formed by organic molecules with strongly anisometric shape. In the simplest nematic LC molecular axes (say, the long axes of the rod-like molecules) orient on average along a unique direction called the director, n. There are no long-range correlations in the molecular positions, so that the material can freely flow as a fluid. However, the nematic fluid has anisotropic properties, like a true crystal. From the optical standpoint, a uniformly oriented nematic is a uniaxial monocrystal with n being its optic axis.
Molecular interactions responsible for the orientational order are rather weak and n can be easily disturbed by many factors, for example, by magnetic or electric field. It is precisely this sensitivity that explains why LCs are so widely used in modern displays and other optical applications. This sensitivity also allows one to link liquid crystallinity to some structural features of biological objects.
|
|
|
|
| Home | Next |