Polymer Liquid Crystals. Behzad Pourabbas Polymer Eng. Dep. Sahand University of Technology Tabriz, Iran [email protected] www.sut.ac.ir. Crystals which are liquid or liquids with properties of crystals. Liquid Crystals States between crystalline and isotropic liquid. Overlook.
States between crystalline and
Liquid crystals form from organic compounds and is thought of as the phase of matter between the solid and liquid state of a crystal. This phenomena was discovered in 1888 by Austrian chemist FrederichReinitzer.
Before discovery of LC, Lehmann designed a microscope that could be used to monitor phase transition process.
Georges Freidel in 1922
Collins PJ (1997) Introduction to liquid crystals: chemistry and physics, vol 1.Taylor and Francis, New York.
where θ is the angle between the molecular axis and the director, and the braces <> denote an average for the material (or a layer). We see from the Eq. that in a completely isotropic system s = 0 while a System perfectly aligned along the director would have s = 1.
S = ½<(3cos²θ-1)>
The order parameter in a liquid crystal range from 0.3 to 0.9
A cholesteric phase is formed by a pile of nematic phases with the director changing from one layer to another;
Smectic phases have also layers, but each layer has at least one more element of long-range order in addition to the director.
The simplest among LC phases are nematic, in which the orientation along the director is the only kind of long-range order present;
An example of a nematic (a), cholesteric (b)
and smectic C (c) phase.
Smectic Liquid Crystals
A type: molecular alignment perpendicular to the surface of the layer, but lack of order within the layer.
B type: molecular alignment perpendicular to the surface of the layer, having order within the layer.
C type: having a tilted angle between molecular alignment and the surface of the layer.
Self-organized pattern of a nematic liquid crystal created by interface orientations at the liquid crystal-isotropic phase transition temperature