The Effect of the Reduction of the Available Surface Area on the Hemicyanine Aggregation in Laterally Organized Langmuir Monolayers

Abstract

This paper analyzes the effect of the reduction of the available area on the aggregation of an hemicyanine dye, 4-[4-dimethylamino)styryl]-1-docosylpyridinium bromide (SP), at the air–water interface. Mixed films of SP and stearic acid (SA) in 1:1 molar ratio have been studied, and compared with the previously studied films of SP and dimyristoyl-phosphatidic acid (DMPA) in 1:1 molar ratio. With regard to the SP:DMPA films, the replacement of DMPA by SA involves reducing the area available for the hemicyanine aggregation, since the SA molecule provides only an alkyl chain to the set, whereas the DMPA molecule provides two alkyl chains to the set. The SP:SA mixed films have been studied by Grazing Incidence X-ray Diffraction (GIXD), Brewster angle microscopy (BAM), and reflection spectroscopy at the air–water interface. Langmuir–Schaeffer films have been studied by UV–vis transmission spectroscopy. The SP:SA mixed monolayer forms star-shaped domains with inner textures, indicating anisotropy. Circular domai...