Self-screening of Langmuir-Blodgett films by a discotic micellar lyotropic liquid crystal

Abstract

The influence of the surface treatment on the anisotropic part of the surface tension of a lyotropic discotic micellar nematic liquid crystal doped with ferrofluid is analysed. The treatment involves Langmuir-Blodgett (LB) films deposited on the glass substrates. Textural observations and phase-shift measurements of the transmitted light were carried out. A phenomenological model which allows calculation of the director average orientation in the bulk and at the surfaces is used for interpreting the experimental data. Our results show that the average director alignment depends on the concentration of the magnetic grains of ferrofluid at the glass surfaces. On the contrary, it is practically independent of the nature of the molecule deposited on the glass substrate. According to the model, the flat glass surface, independently of the treatment or the absence of any treatment, stabilizes onto itself 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 nematic mesophase.