Self-aggregation and phase separation of a styryl dye in monolayer at the liquid–air interface and in Langmuir–Blodgett films

Abstract

The styryl dye 4-[2-[6-(dioctylamino)-2-naphthalenyl]ethenyl]-1-(3-sulfopropyl)-pyridinium inner salt, (Di-8-ANEPPS), was incorporated in mixed Langmuir, (L), monolayers with the cationic surfactant, octadecyltrimethylammonium bromide, (OTMA). The stability of the monolayers was found to vary with the surface pressure and the amount of the diluent in the mixtures. The organization of the dye at the interface, deduced from surface pressure–area, π–A, and surface potential–area, ΔV–A, isotherms, is compared with the spectroscopic data in Langmuir and Langmuir–Blodgett, (LB), films. UV–visible absorption spectra of the pure dye and of the mixtures in L and LB monolayers show the formation of aggregates or domains of Di-8-ANEPPS within the matrix at high amphiphile content. On the contrary, successful transfer of the monomeric form of the dye was achieved using small molar fraction of the cationic matrix.