Unique Interfacial Phenomena on Macroscopic and Colloidal Scales Induced by Two-Dimensional Phase Transitions

Abstract

This feature article addresses a variety of unique macroscopic-scale and colloidal-scale interfacial phenomena, such as wetting transitions of oil droplets into molecularly thin films, spontaneous merging and splitting of oil droplets at air-water interfaces, solid monolayer and bilayer formation in mixed cationic surfactant/alkane adsorbed films, switching of foam-film thickness, and oil-in-water emulsion stability. All of these phenomena can be observed using commercial cationic surfactants, liquid alkanes, and water.

Surface Phases and Surface Freezing in an Ionic Liquid

“…The discussion above indicates a 3–5-fold outnumbering of the cation tails by the guest molecules in the LG monolayer. Similar and even larger, >10-fold, outnumberings were found in conventional LG films at the water/air ,− and water/alkane interfaces. Although a minority, the tail’s presence in the conventional LG film was found to be mandatory for inducing SF in the monolayer .…”

“…Conventional LG films ,− form when a liquid alkane droplet, which does not spread on pure water, is placed on the free surface of an aqueous solution of a surfactant comprising an alkyl tail of length similar to that of the droplet’s alkane. The Gibbs-adsorbed surfactant layer residing at the solution’s surface induces migration of alkane molecules from the droplet along the surface, and a monolayer of mixed alkane molecules and air-protruding surfactant tails forms on the solution’s free surface.…”