PHASE-TRANSITIONS IN FINITE-THICKNESS NEMATIC LIQUID-CRYSTAL FILMS - PLANAR ANCHORING

Phase transitions in finite-thickness nematogenic materials bounded by two planar surfaces and characterized by identical surface interactio ns linearly proportional to the order parameter have been studied theo retically by solving the coupled nonlinear Euler-Lagrange equations. T he surface interaction was assumed to favor molecular orientation in t he surface plane with no rubbed or preferred direction. The related pr oblem of a semi-infinite film having a single surface has been studied previously at temperatures above the bulk nematic-isotropic phase tra nsition point T-NI. For that geometry and physically relevant elastic constants, it was shown that, in addition to the bulk transition, ther e is a second transition at higher temperatures between biaxial and un iaxial ordering of the surface layer when the strength of the surface coupling is not too weak. It is shown here that this double phase tran sition reduces to a single one for sufficiently thin layers.