LUBRICATION THEORY FOR NEMATIC LIQUID-CRYSTALS

Liquid crystals have elongated molecules which tend to orient in a particular direction. Layered (smectic) liquid crystals have demonstrated promise as lubricants. In smectics, the microstructure is ordered Iry position and orientation; while in nematics, the topic of the present paper, the ordering is only Iry orientation. Nematics have been proposed as lubricants, and may also be used to study the effect of microstructure on tribological properties. The molecular orientation may be varied by application of an electric or magnetic field. In the present paper, the fundamental continuum ¡low theory is applied to the lubrication geometry. The angular momentum (couple) equation must be taken into account to determine molecular orientation by solving for a so-called director. Friction and load behavior are computed as functions of a couple viscosity parameter which depends on the relative effects of viscosity and electromag-netism. This behavior may be quasi-Newtonian in nature or highly non-Newtonian depending on the couple viscosity parameter and material properties. © 1990 Taylor & Francis Ltd.