Alignment of liquid crystal and dichroic dye molecules in mixed Langmuir and Langmuir-Blodgett films

Abstract

A study of dichroic dye-liquid crystal mixtures (guest-host systems) in monolayers formed at a gas-liquid interface (Langmuir lms) and at a solid surface (Langmuir-Blodgett lms) has been made. As a host 4-n-octyl-4¾ -cyanobiphenyl (8CB) or 4-n-pentyl-4 ² -cyano-p-terphenyl (5CT) were chosen, while three dichroic azo dyes with various molecular structures were used as guest species. The dyes were added to the liquid crystal matrices at a concentration corresponding to the whole range of molar fractions and the surface pressure-mean molecular area isotherms for Langmuir lms were recorded. On the basis of the isotherms, conclusions about the molecular organization and the miscibility of the components in the ultrathin lms were drawn. The Langmuir lms were transferred onto the quartz plates at surface pressures below the collapse point. The polarized absorption spectra of the Langmuir-Blodgett lms were recorded and information about the alignment and intermolecular interactions in the mixtures of the non-amphiphilic dichroic dyes and the liquid crystals with strongly polar terminal groups were obtained.

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

“…This means that none of the azo dyes under investigation cannot produce stable and compressible monolayer, although all they possess terminal and/or lateral polar group. Similar behaviour was noticed for azo dyes investigated previously [7][8][9][10]. However, when the dyes were mixed with 8CB at appropriate concentrations, the compression was possible and we obtained π-A isotherms.…”

“…Some years ago in our laboratory the study of the molecular organization and aggregation in the Langmuir and Langmuir-Blodgett films formed of azo dyes mixed with a liquid crystal, using as a stabilizing matrix, had been undertaken [7][8][9][10]. Our present work, that was carried out as the continuation of the previous study, has aimed at reporting several additional observations related to the intermolecular interactions on the molecular level.…”