Liquid Crystals

Chapter 1.3 - Lyotropic, Polymeric, and Thermotropic Liquid Crystals

1.3.   LYOTROPIC, POLYMERIC, AND THERMOTROPIC
LIQUID CRYSTALS


One can classify liquid crystals in accordance with the physical parameters controlling
the existence of the liquid crystalline phases. There are three distinct types of liquid
crystals: lyotropic, polymeric, and thermotropic. These materials exhibit liquid
crystalline properties as a function of different physical parameters and environments.

1.3.1.   Lyotropic Liquid Crystals

Lyotropic liquid crystals are obtained when an appropriate concentration of a material
is dissolved in some solvent. The most common systems are those formed by water and
amphiphilic molecules (molecules that possess a hydrophilic part that interacts
strongly with water and a hydrophobic part that is water insoluble) such as soaps, detergents,
and lipids. Here the most important variable controlling the existence of the liquid
crystalline phase is the amount of solvent (or concentration). There are quite a
number of phases observed in such water-amphiphilic systems, as the composition and
temperature are varied; some appear as spherical micelles, and others possess ordered
structures with one-, two-, or three-dimensional positional order. Examples of these
kinds of molecules are soaps (Fig. 1.8) and various phospholipids like those present in
cell membranes. Lyotropic liquid crystals are of interest in biological studies.2

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