Study of mixed system in monolayers and multilayers transferred by Langmuir–Blodgett technique

Abstract

Mixtures in different molar proportions of azo acid, (6Az10COOH, 6A10) and arachidic acid (AA) when spread on an aqueous subphase containing CdCl2, were found to form inhomogeneous monolayers on the water surface. This inhomogeneity in the monolayers at the air–water interface as well as in the transferred films was studied by using π–A isotherms, XRD and UV–visible spectroscopy. π–A isotherm studies of the monolayers and XRD, UV–visible spectroscopy of Langmuir–Blodgett (LB) multilayers essentially indicated that there was microphase separation. Domains of azo acid and arachidic acid were found. H-aggregate formation of azo acid was observed in pure azo acid as well as in the azo acid composite films. Composite LB films consist of three different phases of molecular organizates and one of these involves molecular arrangement where domains of azo acid and arachidic acid straddle each other. Studies showed that strong molecular interaction in the successive layers in the mixed system led to this characteristic molecular packing in the system. The mean molecular area, ΔGexπ and collapse pressure also showed that the acids were immiscible, thus indirectly suggesting the presence of domains in the system.