Phase separation in mixed monolayers of arachidic acid and a phthalocyanine of zinc

Abstract

Mixed Langmuir and Langmuir-Blodgett films of dissimilar components, arachidic acid and a phthalocyanine of zinc, have been investigated. These compounds form mixed films with phase separation, with domains at the sub-micro scale which are detected by AFM in LB films but not observed by BAM. These domains present different contrast in the surface potential images obtained with SP-AFM and in the friction images. The analysis of the isotherms and of the AFM images, at several compositions, reveals that the components are immiscible. The difference in height between the arachidic acid and the phthalocyanine of zinc phases is in accordance with the heights of the molecules, and points to the presence of a monolayer in the zinc phthalocyanine phase. AFM has revealed as a necessary technique to elucidate the miscibility in mixed films at the nanometric scale. UV-Vis spectroscopy shows changes in the spectra bands of LB films in respect to those in solution, due to the organization of the molecules in the LB film.

Interactions of cryoprotective agents with phospholipid membranes - A Langmuir monolayer study

“…40,41 ). The effects of solutes on lipid organization can be assessed in terms of the changes in the area per lipid molecule, phase transition pressures and inverse compressibility modulus values 34,[42][43][44] . These can be directly related to the properties of bilayers: for example, the gel and fluid phases of a bilayer are analogous to the liquid condensed and liquid expanded phases, respectively, of a monolayer 35,[45][46][47] .…”

Organization of the Interfacial Film of Nanoemulsions Stabilized by Porphyrin Derivatives

“…However, it also seems that the reorganization of GTO and Pyro-A molecules participate in the smoothing of the monolayer. Torrent-Burgués observed that a fatty acid mixed with a phthalocyanine contributes to the formation of a more uniform phase despite the phase separation between the two immiscible compounds.…”

“…However, BAM images show that after a few compression cycles, the morphology of monolayers containing high Pyro-A molar fraction appears more uniform. Torrent-Burgués observed a decrease in the compactness of a phthalocyanine monolayer when mixed with a fatty acid due to the insertion of fatty acid chains between the photosensitizer molecules. Thus, the organization of densely packed Pyro-A molecules after partial collapse of GTO molecules might still be impacted by the triglyceride.…”