Phase Separation of Palmitic Acid and Perfluorooctadecanoic Acid in Mixed Langmuir−Blodgett Monolayer Films

Abstract

Deposition of mixtures of palmitic acid (C15H31COOH) and perfluorooctadecanoic acid (C17F35COOH) onto solid substrates gives rise to irregularly shaped, phase-separated domains under a variety of deposition conditions. The morphology and chemical composition of these phase-separated domains have been investigated using a combination of surface pressure-area isotherms, atomic force microscopy, X-ray photoemission electron microscopy, and confocal fluorescence microscopy imaging. While domain morphology and composition in 2D phase-separated mixed monolayer systems can typically be rationalized in terms of an interplay between line tension and dipole-dipole repulsion effects, it was found that for this system additional kinetic factors, including domain growth rates and the rate of dissolution of the fatty acid component into the aqueous subphase, also play a major role in controlling film properties. The potential importance of these effects for the controlled patterning of solid substrates is discussed.

The influence of salinity on surfactant miscibility in mixed dipalmitoylphosphatidylcholine – perfluorooctadecanoic acid monolayer films

“…Isotherms for C18F consisted of a single, smooth curve which did not contain a LE-LC transition, and a film collapse pressure of $65-68 mN/m, which is again consistent with isotherms we have reported previously in the literature [11]. As was the case with DPPC, there were no shifts or new phase-transitions observed for the pure C18F isotherm as a function of subphase salinity.…”

“…The film morphology and composition in these immiscible systems is regulated by a combination of inter-related factors, including dipole-dipole repulsion between charged surfactant headgroups, line-tension, kinetics of surface domain growth, substrate-mediated condensation and hydrodynamic flow effects [2,5,7,8,10,11]. Further control of film morphology has been demonstrated by exploiting solubility of the components in an aqueous subphase, as well as through kinetic control of the phase-separation process [10,11]. Through careful manipulation of these factors, a wide range of different film morphologies can be prepared, ranging from circular domains to nanoscale wires and lines [3].…”

Langmuir Monolayer Miscibility of Perfluorocarboxylic Acids with Biomembrane Constituents at the Air-Water Interface

“…the line tension at the boundary between DMPE and F17COOH. A similar type of phase separation for the binary fatty acid/FnCOOH monolayers has been reported by Qaqish et al 75,84,85 .…”

“…When unpurifi ed FnCOOH was used in the isotherm measurements, various A 0 values were generated: A 0 0.32 0.35 nm 2 for n 11 50,73 47,49,50,75 . In the case of unpurifi ed F13COOH in particular, the A 0 value was unreasonable in terms of the estimated cross-sectional area of the perfluorocarbon chain, which implies that unpurifi ed F13COOH possibly contains a small amount of longer-chain FnCOOH n 13 as an impurity.…”

Hydrophobic coating of mica by stearic acid vapor deposition

“…While the structures of films transferred to flat and well defined substrates such as mica, silica, gold, etc. were well established for films with a single type of molecules [9], the structure of films presenting mixtures of different molecules is still under debate [11]. Multilayer films are usually created by sequential transfers using this method.…”