Molecular organization in binary mixtures of derivatives of naphthalenebicarboxylic acid and naphthoylenebenzimidazole with a liquid crystal in two-dimensional layers

Abstract

Langmuir films of some dichroic dyes, namely derivatives of naphthalenebicarboxylic acid and derivatives of naphthoylenebenzimidazole, as well as of their mixtures with the liquid crystals 4-octyl-4′-cyanobiphenyl (8CB) and 4-pentyl-4″-cyano-p-terphenyl (5CT) were prepared. Surface pressure/mean molecular area isotherms were recorded from which some information about the alignment of molecules in a monomolecular layer at an air–water interface could be deduced. It was found that the properties of the monolayer are highly sensitive to the molecular structure of the side groups substituted on the main skeleton of the dye molecule, and to the mixture composition. Moreover, information about the miscibility or the phase separation of the two components in Langmuir films formed from dye/liquid crystal mixtures was obtained by using the excess area criterion and surface pressure rules.