Non-Debye screening of a surface charge and a bulk-ion-controlled anchoring transition in a nematic liquid crystal

We study the anchoring mechanism due to substrate-adsorbed ions by examinin g a related anchoring transition. An analytical solution to the Poisson equ ation shows that, as their number suffices for a non-negligible anchoring c ontribution, the surface field is screened over some characteristic microsc opic distance. It is shown both theoretically and experimentally that the c ritical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions. [S1063-651X(99)17710 -9].