Chapter 3 87 fiber interface and the soil will be removed by emulsification (Figure 12). Emulsification is favored by low oil/water interfacial tension which allows the oil surface to be expanded into an emulsion droplet.30 In the penetration mechanism of oily soil removal, surfactant- rich phases penetrate the oil at the interface. This results in an interfacial liquid crystalline phase that swells and is broken off to reveal a fresh soil interface, and then the process is repeated again and again.31 The penetration mechanism occurs with polar soils and/or phase separated coacervates of nonionic surfactants above the lower critical solution temperature (LCST). Spontaneous emulsification, in the absence of detersive surfactant, has been observed for non-polar-polar soil mixtures like sebum.32 The penetration mechanism can occur with anionic surfactants that form coacervate phases in the presence of calcium salts.33 Solubilization is the process of incorporating a water-insoluble hydrophobic substance in the internal hydrophobic core of micelles. Direct solubilization can occur in the presence of an excess of surfactant micelles with respect to oily soil.34 The rate of exchange of surfactant molecules between micelles is important because the micelles must re-assemble around the soil to solubilize the soil by encompassing it inside the micelle. Foam/Lather One essential attribute of a shampoo is its ability to produce a rich lather. The important elements of a foam are the lamellae and the Plateau border. The micrograph in Figure 13 depicts Figure 12. Emulsification can remove the soil if the interfacial tension between the oily soil and the surfactant solution is low.