Liquid crystals - these are substances that are in mesomorphic (average intermediate) between isotropic liquid and crystalline solid.These elements have fluidity can be in the form of droplets.Together with the manifestation of these properties, the liquid crystals exhibit anisotropic magnetic, electrical, optical, and other properties associated with molecular ordering in the orientation.In other words, the compounds have multidirectional characteristics.In the absence of external influences in the anisotropic liquid crystal thermal conductivity, electrical conductivity, magnetic susceptibility, the dielectric constant.The substances marked dichroism and birefringence.
Depending on the receiving classified lyotropic and thermotropic liquid crystals.There is also a division into types according to the structure of the molecules.
smectic liquid crystals
first found them in the soap (hence the name - "smegma" - soap).Ends of the molecules as they are fixed in perpendicular to the longitudinal axes of the planes.Smectic liquid crystals are different layered structure.These substances include aqueous solutions of soaps, acid ethyl ester azoksibenzoynoy.
"smectics" considered the most extensive class of liquid crystals.Some varieties show and ferroelectric (the presence of the spontaneous polarization in a certain temperature range).High viscosity prevented find widespread use of smectic liquid crystals in the art.
Nematics
Nematic liquid crystals are different longitudinal orientation of the molecular axes in some direction.In other words, they are characterized by long-range orientational order.Name crystals derived from the Greek definition of "dumb" - thread.Disinclinations (thread) have a high mobility in natural light are clearly visible.
cholesteric liquid crystals and their application
molecular forms of substances of this type are arranged in parallel oblong plate.Cholesterics give propyl ether cholesterol holesteriltsinnamat, other derivatives of cholesterol.
thermoindicators cholesteric liquid crystals are widely used in medical and technical dianostike.The sensitivity of these materials to the temperature allows you to visualize the temperature distribution on the surface.This, in turn, is used in imaging (observation processes inside the bodies, optically opaque), the detection of certain diseases, as well as temperature sensors.These crystals form a temperature pattern in the form of a color chart.Cholesterics may also be used in the imaging of microwave fields.For the production of the indicators used by the effect of dynamic light scattering.In the liquid crystal display applies the ambient light.This significantly reduces power consumption.Thus, the power LCDs are much lower than in the film and powder phosphors, LED, discharge indicators.Cholesterics used to transform into a visible image infrared.
in cholesteric liquid crystals (unlike nematic) dynamic scattering of light can have a memory - the state, the scatter light may persist after removal of the field.At the same time certain properties of the cholesteric influence the duration of the condition.Thus, the memory can be maintained from a few minutes up to several years.In the initial state (nonscattering) cholesteric alternating voltage leads.This property is used in the formation of memory cells.
