Читать книгу Liquid Crystals - Iam-Choon Khoo - Страница 38

Above T_c, liquid crystals lose their directional order and behave in many respects like liquids. All bulk physical parameters also assume an isotropic form, although the molecules are anisotropic.

The isotropic phase is, nevertheless, a very interesting and important phase for both fundamental and applied studies. It is fundamentally interesting because of the existence of short‐range order, which gives rise to the critical temperature dependence of various physical parameters just above the phase transition temperature. These critical behaviors provide a good testing ground for liquid crystal physics.

On the other hand, recent studies have also shown that isotropic liquid crystals may be superior in many ways for constructing practical nonlinear optical devices (see Chapter 12), in comparison to the other liquid crystalline phases (see Chapter 8). In general, the scattering loss is less and thus allows longer interaction lengths, and relaxation times are on a much faster scale. These properties easily make up for the smaller optical nonlinearity for practical applications.