Molecular organization and aggregation in Langmuir and Langmuir-Blodgett films of azo dye/liquid crystal mixtures

Abstract

A study of azo dye/liquid crystal mixtures in monolayers formed at air-water (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces was performed. Three azo dyes with various molecular structure and two liquid crystal materials: 4-octyl-4′-cyanobiphenyl (8CB) and trans-4-octyl(4′-cyanophenyl)-cyclohexane (8PCH) were used. The morphology of Langmuir films was monitored by means of a Brewster angle microscope (BAM). Moreover, a surface pressure and electronic absorption spectra of the monolayer spread on the water surface of dye/liquid crystal mixtures as a function of a mean molecular area were simultaneously recorded. In addition, the absorption for Langmuir-Blodgett films deposited on quartz plates was measured. 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. The influence of the dye molecular structure and its concentration on aggregates’ geometry was found.

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.…”

“…We found that dyes 1 and 2 behave similarly as the dyes from Refs. [8,10]: at a low dye content in the mixture the monomers and some fraction of J-type dimers occur, whereas at X M = 0.5 the monomers, J-dimers and H-dimers in various fractions exist. In the case of dyes 4 and 5 the creation of J-dimers was observed only.…”

“…However, the shift of the maximum position is different for various dyes. For the azo dyes studied previously, it was found [8,10] that at low concentrations of a dye in the Langmuir and LB films the absorption maximum position shifts towards longer wavelengths with respect to the position of the monomeric absorption band. Upon increasing the content of the dye, the wavelength of the maximum band shortens.…”

Molecular-level interactions of an azopolymer and poly(dodecylmethacrylate) in mixed Langmuir and Langmuir–Blodgett films for optical storage

“…As discussed for other polymers [25], a quantitative interpretation of surface potential measurements is still not possible for macromolecules. Brewster angle microscopy (BAM) was used to study the morphology of the Langmuir films and possible interactions between the polymers in the mixture [26]. For neat HPDR1-MA, Fig.…”