Wetting in oil/water/surfactant systems

The behaviour of oils at aqueous interfaces is ubiquitous to many industrially and biologically relevant processes. In this review we consider modifications to the wetting properties of oils at the air/water, oil/water and solid/liquid interfaces in the presence of surfactants. First-order wetting transitions can be induced in a wide range of oils by varying the aqueous surfactant concentration, leading to the formation of mixed monolayers at the interface. In certain cases, these mixed monolayers display novel surface freezing behaviour, including the formation of unusual bilayer structures, which further modifies the properties of the interface. The effects of surfactant on line tension at the three-phase contact line and differences between the air/liquid and liquid/liquid interfaces are discussed.

The behaviour of oils at aqueous interfaces is important in both nature and industry, and is modified by the presence of surfactants. First-order wetting transitions can be induced, resulting in mixed monolayer formation. Surface freezing of these mixed monolayers can lead to novel surface phases, including unusual bilayer structures. Changes in line tension at the three-phase contact line are discussed.Figure optionsDownload high-quality image (115 K)Download as PowerPoint slideHighlights
► Surfactants can induce first-order wetting transitions at the air/water interface.
► Surface freezing leads to formation of novel structures at fluid/fluid interfaces.
► Line tension changes sign at both wetting and surface freezing transitions.