Intermolecular interactions in Langmuir and Langmuir-Blodgett films of azo dye/liquid crystal mixtures

Binary mixtures of the dichroic azo dye with the liquid crystal as Langmuir and Langmuir-Blodgett films have been studied. Four azo dyes with various molecular structure and liquid crystal materials: 4-octyl-4'-cyanobiphenyl (8CB) and trans-4-octyl(4'-cyanophenyl)-cyclohexane (PCH8) were used. The surface pressure as a function of the mean molecular area for Langmuir films were, measured and the organization of molecules at the air-water interface was determined. Absorption spectra in situ for Langmuir films and absorption spectra by using both natural and linearly polarized light for Langmuir-Blodgett films were recorded and information about intermolecular interactions in the mixtures of the nonamphiphilic dye and the liquid crystal with polar terminal group was obtained. Conclusions about the formation of self-aggregates between dye molecules have been drawn.