Field Behavior of the Isotropic Phase

FIGURE 4.37. The angles of total internal reflection ixiR versus reduced voltage in two types of the Prederiks transition [210]. (a) B-effect and (b) S-efFect (Fig. 4.1 (a, b)). Dots—experiment, solid lines—calculations, dashed line—qualitative estimation (4.85). 

The isotropic phase of nematogens differs from conventional isotropic liquids in two aspects. First, the pretransitional phenomena in the vicinity of the clearing point dramatically change the bulk properties (in particular, the Kerr constant) of the isotropic phase due to the short-range nematiclike order. Second, quasi-nematic surface layers form at the interface with a solid substrate. Due to their dielectric (and optical) anisotropy they can contribute to the electrooptical properties of cells filled with the isotropic phase. For example, they can be reoriented by an external field (an analogy with the Frederiks transition). We will discuss briefly both phenomena. 

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