Wetting of low free energy surfaces by aqueous surfactant solutions

Surfactant-enhanced spreading of water-based formulations over low-energy surfaces has attracted considerable interest in scientific and industrial communities because of its importance in agrichemical, pharmaceutical, coating and textile applications. Spreading of aqueous surfactant solutions is rather complex process than spreading of pure liquids due to a time-dependent adsorption/desorption of surfactant molecules at all three interfaces involved that results in changing the interfacial energy balance, producing interfacial tension gradients and, hence, Marangoni flows. The phase behavior and structures of surfactant aggregates in bulk solutions, structure and surface activity of surfactant molecule itself, physicochemical properties of substrates and a number of other parameters could strongly influence spreading dynamic of surfactant solutions on hydrophobic surfaces. Implication of all those factors on spreading behavior of solutions makes it hardly predictable from both theoretical and practical points of view. In this brief review we summarize different factors that determine spreading character of aqueous surfactant solutions on hydrophobic substrates such as polymers films and chemically modified solids. Focus is made on spreading and wetting behavior of nonionic hydrocarbon and organosilicone surfactants, which are widely used in commercial and analytical applications.