Ionic adsorption and equilibrium distribution of charges in a nematic cell

We consider the steady-state distribution of ionic charges in a nematic sam ple of slab shape, whose limiting surfaces are supposed to adsorb positive ions. Our analysis allows the calculation of the electrical potential at th e surfaces and in the bulk, and of the chemical potential versus the thickn ess of the sample d, The surface density of ions and the intensity of the e lectric held in the double layer are evaluated in terms of d. In the Limit of small d we show that the surface density of adsorbed ions is proportiona l to the thickness, whereas in the opposite limit of large d it is nearly i ndependent of it. We analyze also the influence of the surface charges on t he effective anchoring energy of nematic liquid crystals, as well as the th ickness dependence of this parameter. Our analysis generalizes similar calc ulations previously published. [S1063-651X(99)08902-3].