ANCHORING ENERGY FOR THE NEMATIC LIQUID-CRYSTAL LANGMUIR-BLODGETT-FILM INTERFACE

We analyse the effect of a Langmuir-Blodgett (LB) multilayer on the su rface properties of a nematic liquid crystal (NLC). We show that the e asy axis of the LB-NLC interface coincides with that of the LB-solid s urface interface. On the contrary, the effective anchoring energy of t he LB-NLC interface is lower than that associated with the LB-solid su bstrate interface. We show in a first approximation that the anchoring energy characterizing the NLC may be separated into three contributio ns: one connected with the interaction between the LB him and the soli d substrate, one due to the direct LB-NLC interaction and the other on e having an elastic origin. Nevertheless, to be more precise, one has to consider also the term associated with the interaction energy betwe en the NLC and the substrate, which is screened by the LB him. The ela stic contribution is of the order of the elastic constant of the LB hi m 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.