Anchoring energy for the nematic liquid crystal–Langmuir Blodgett film interface

Abstract

We analyse the effect of a Langmuir-Blodgett (LB) multilayer on the surface properties of a nematic liquid crystal (NLC). We show that the easy axis of the LB-NLC interface coincides with that of the LB-solid surface interface. On the contrary, the effective anchoring energy of the LB-NLC interface is lower than that associated with the LB-solid substrate interface. We show in a first approximation that the anchoring energy characterizing the NLC may be separated into three contributions: one connected with the interaction between the LB film and the solid substrate, one due to the direct LB-NLC interaction and the other one having an elastic origin. Nevertheless, to be more precise, one has to consider also the term associated with the interaction energy between the NLC and the substrate, which is screened by the LB film. The elastic contribution is of the order of the elastic constant of the LB film over the thickness of the multilayer. This quantity is estimated to be of the order of 10⁻²–10⁻¹ erg cm⁻², as experimentally observed. Possible extensions of our model are also discussed.