MICROSCOPIC THEORY OF ANCHORING TRANSITIONS AT THE SURFACES OF PURE LIQUID-CRYSTALS AND THEIR MIXTURES .2. THE EFFECT OF SURFACE-ADSORPTION

We have extended our theory of anchoring transitions to take into account adsorption at the interface between a nematic-non-nematic binary mixture and a solid aligning substrate. This was achieved by decoupling adsorption and anchoring and treating the former in the context of the Cahn theory of wetting, while the latter was studied using our previous anchoring theory. For ease of calculation, we mapped the relevant portion of the phase diagram of the mixture onto that of a (isotropic) regular solution. The anchoring angle has been calculated over the whole concentration range, in the partial wetting regime, and in the near saturation region, in the complete wetting regime. For realistic values of the molecular parameters, anchoring transitions have been found which exhibit a degree of temperature independence ('universality') akin to that observed experimentally. Ways of developing a fully consistent theory of anchoring transitions are also briefly discussed.