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What are Liquid Crystals?

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Mesophases (liquid crystals and plastic crystals) are a state of order between crystals and liquids. They have imperfect long range orders of orientation and/or position. Thus, the can be fluid like a liquid and they can have anisotropic properties like crystals. Whereas the plastic crystals have a predominating positional order, the liquid crystals have a predominating orientational order.

The main reasons for the formation of liquid crystalline phases are:

  • a simple geometrical form of the molecule: rods, discs or ball, which allow a closer packing in a mesophase (monophilic liquid crystals).
  • an intramolecular contrast, which cases microseparation of different parts of the molecules (amphiphilic liquid crystals).

molecular packing of crystals, liquids and plastic crystals

The simplest liquid crystalline phases are the nematic phases, which have no positional order.

molecular packing of various nematic liquid crystals

Smectic phases have layered structures.

molecular packing of various smectic liquid crystals

The term liquid crystals covers a wide area of chemical structures, physical properties and technical applications.

Typical chemical structures are:

  • cholesterol ester
  • phenyl benzoates
  • surfactants
  • paraffines
  • glyco lipids
  • cellulose derivatives
Typical applications are:
  • LCD displays (STN, FLC, TN, etc.)
  • dyes (cholesterics)
  • advanced materials (Kevlar, Vectra)
  • membrans
  • temperature measurement (by changing colors)
  • solvents for GC, NMR, reactions, etc.
  • effect colors

Last Change: 5.8.2003, 04:24 pm by Volkmar Vill
Design: Matthias Vill 2003 | Contact: Volkmar Vill