1. P.-G. de Gennes and J. Prost The Physics of Liquid Crystals (Clarendon Oxford 1993).
2. R. Jowitt et al. Eds. Physical Chemistry of Foods (Applied Science New York 1983).
3. L. E. Nielsen and R. F. Landel Mechanical Properties of Polymers and Composites (Dekker New York ed. 2 1994) chap. 7.
4. We investigated cholesteric LCs with pitch p ranging from 0.5 to 15 μm produced by doping a nematic consisting of a mixture of cyanobiphenyls with a small concentration of chiral molecules. Optical observations were carried out in thin films of width D film ranging from 20 to 100 μm between microscope slides; thicker films lead to excessive light scattering and preclude the direct observation of their defect structure. The glass slides were coated with rubbed polyimide to enforce a parallel boundary condition at the surface for the nematic director n which specifies the average local orientation of the molecules. In this case the lowest free-energy state of the pure cholesteric is the planar texture (1) characterized by horizontal layers connecting points of equal orientation of n (Fig. 1A). The cholesteric twist axis t in this configuration is oriented perpendicular to the film and layers of equivalent orientation of n are spaced by the distance h = p /2.
5. P. Poulin and O. Mondain-Monval unpublished data.