DRY-FRICTION AND CRITICAL-STATE IN LYOTROPIC NEMATIC LIQUID-CRYSTALS IN A MAGNETIC-FIELD

The surface properties of planarly oriented lyotropic nematic liquid c rystals are theoretically described by means of a model based on the d ry-friction like interaction among the nematic molecules and the solid substrate. The new critical state and the orientation induced by an o blique magnetic field on lyotropic nematic liquid crystals are analyse d, It is shown that there exists a critical field beyond which the reo rientation induced by the magnetic field becomes an irreversible pheno menon. The relation connecting this critical field with the surface to rque due to the dry friction is obtained in the framework of the conti nuum theory.