Liquid crystals

Liquid crystals are substances that show a phase of matter that has properties between those of a conservative liquid, and those of a solid crystal. For instance, a liquid crystal (LC) might flow like a liquid, but have the molecules in the liquid arranged and leaning in a crystal-like way. There are many dissimilar types of LC phases, which could be distinguished based on their different optical properties (such as birefringence). When viewed under a microscope by a polarized light source, a liquid crystal material would emerge to have a distinct texture.

Each 'patch' in the texture corresponds to a field where the LC molecules are oriented in a dissimilar direction. Within a domain, however, the molecules are well ordered. Liquid crystal materials might not always be in an LC phase (just as water is not always in the liquid phase: it might also be found in the solid or gas phase). Liquid crystals could be divided into thermo tropic and allotropic LCs. Thermo tropic LCs show a phase transition into the LC phase as hotness is changed, whereas allotropic LCs exhibit stage transitions as a function of concentration.

Microscopic theoretical action of fluid phases could become quite involved, owing to the high material density that means that strong interactions, hard-core repulsions, and many-body correlations cannot be unseen. In the case of liquid crystals, anisotropy in all of these connections further complicates analysis. There are a number of quite simple theories, however, that could at least predict the general behavior of the stage transitions in liquid crystal systems.

Molecules that display liquid crystal phases are called mesogens. For a molecule to display an LC phase, it should usually be rigid and anisotropic (i.e. longer in one direction than another). Most mesogens fall into the 'rigid-rod' class (calamity mesogens) that orient based on their long axis. Disk-like (disco tic) mesogens are also known, and these familiarize in the direction of their short axis. In addition to molecules, polymers and colloidal suspensions could also form LC phases. For instance, micrometer-sized objects (such as anisotropic colloids, latex particles, clay platelets, and yet some viruses, such as the tobacco mosaic virus) could organize themselves in liquid crystal phases.