softmatter:Liquid Crystal

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Liquid crystalline structures are structures where there is a tendency of the molecules to align and point along a common axis, called the director. Typically liquid crystals are found for rod like molecules. Liquid crystals exist intermediate between traditional crystalline phases with long range order and liquid phases with no directional or long range order. Typically liquids are isotropic, meaning they are indistinguishable regardless of the direction of measurement. Liquid crystals, on the other hand, often are anisotropic, making them desirable for optical applications [1,2]].

Nematic Order Parameter

One can measure the degree of order in a rod like system by using the following order parameter [1,2]:

$S= \frac{1}{2}<3cos^2\theta-1>$

where theta is the angle with respect to the director (average direction of the rods) in the system. Typically, crystals gives values of S~1, disordered liquids values of S<0.3 and liquid crystals values of S~0.3-0.9 [1,2].

For more, see the Nematic Order Parameter entry.

Liquid Crystalline Phases

Smectic

Smectics are layered materials that can either be liquid crystalline or crystalline.

• Smectic A

• Smectic C