Phase diagram and morphology of anisotropic domains in a pure and mixed carbocyanine monolayer

Abstract

A film of amphiphilic carbocyanine dye is spread on water and observed by fluorescence and polarized light techniques. With ClO 4 − counterions in the subphase, a first order transition occurs between an isotropic liquid phase and a solid one, made of birefringent elongated domains. On pure or acidified water, this transition takes place at a higher surface pressure, close to the monolayer collapse. When the carbocyanine is mixed with a fraction x of stearic acid another condensed phase appears, made of birefringent disks growing around a central disinclination. We report data concerning the phase diagram, and present a photometric method to measure the film thickness. We also discuss the nature of the different phases, and the possibility of a smectic-to-isotropic transition at x = 0.6.