ABSTRACT
In this chapter, the influence of adsorbed ions and the resulting surface electric field on the anchoring properties of NLC is analyzed. Some elements of the theory of a weak electrolyte are presented to establish the conceptual framework in which the subsequent investigations will be developed. The main elements of the Poisson-Boltzmann theory are presented in a concise way. The consequences of the linear approximation for this theory are investigated. In particular, we consider the influence of the adsorption phenomenon on the anchoring energy to explain the thickness dependence of this quantity. Further, in order to investigate the effect of the surface electric field on the molecular orientation, we present a model that takes into account two physical mechanisms for the coupling of the nematic director with the surface electric field: (i) the dielectric anisotropy and (ii) the coupling of the quadrupolar component of the flexoelectric coefficient with the field gradient. It is shown that for sufficiently large surface fields there can be a spontaneous curvature distortion in the cell even when the anchoring energy is infinitely strong. We also discuss the director distortion when the anchoring energy of the surface is finite.
