SELF-SCREENING OF LANGMUIR-BLODGETT-FILMS BY A DISCOTIC MICELLAR LYOTROPIC LIQUID-CRYSTAL

The influence of the surface treatment on the anisotropic part of the surface tension of a lyotropic discotic micellar nematic liquid crysta l doped with ferrofluid is analysed. The treatment involves Langmuir-B lodgett (LB) films deposited on the glass substrates. Textural observa tions and phase-shift measurements of the transmitted light were carri ed out. A phenomenological model which allows calculation of the direc tor average orientation in the bulk and at the surfaces is used for in terpreting the experimental data. Our results show that the average di rector alignment depends on the concentration of the magnetic grains o f ferrofluid at the glass surfaces. On the contrary, it is practically independent of the nature of the molecule deposited on the glass subs trate. According to the model, the flat glass surface, independently o f the treatment or the absence of any treatment, stabilizes onto itsel f a lamellar layer (or bilayer) formed by the amphiphilic molecules of the liquid crystal. This layer screens the effect of the LB film (or of the pure untreated substrate) on the alignment of the lyotropic nem atic mesophase.