Physical Properties of the Cholesteric Mesophase.

This final report describes experimental research on the behavior of ultrasound in liquid crystals, structure studies of liquid crystals by use of x-ray methods, degree of ordering in a nematic liquid crystal under an electric field, and synthesis of new liquid crystalline compounds. From the theoretical point of view the application of a dipole-dipole model to liquid crystalline systems is presented. For cholesteryl nonanoate the skin-depth penetration of the shear wave was found to be .000002m with a wave velocity of 80 msec at a frequency of 9.45 MH. The small penetration depth makes the shear-wave technique ideally suited for studying surface properties of liquid crystals. Some liquid crystals take on an ordered arrangement on surfaces while others are unordered. The dipole-dipole model of a nematic liquid crystal predicts an antiferroelectric state of order based on dipole-dipole interactions of nearest neighbors. The model also predicts that the nematic-isotropic point should be field dependent. X-ray studies have led to the point where it can give a fairly good classification of liquid crystals based on diffraction patterns. Infrared dichroic studies can be used to establish the degree of ordering of nematic liquids.