ABSTRACT
This chapter discusses the hydrodynamic properties of nematics, and the microscopic principles from which they follow. In the liquid and gas phases the H2O molecules are free to translate and rotate while in the solid both the translational and rotational degrees of freedom are frozen except for small oscillations. Liquid crystals are systems, composed of elongated organic molecules, in which this sequence is reversed. A classical example is para-azoxyanisole. Phenomenologically, the liquid crystalline phases are liquid; for example, nematics flow like liquids. However, they are not isotropic like water. Rather, the electrical, magnetic, and mechanical properties of the nematic mesophase are quite strongly uniaxial. The nematic structure is not the only one found in liquid crystalline systems. There are cholesterics, in which the molecular axes are arranged in a helical pattern, and there are several classes of smectics in which there is also at least some degree of translational order.
