ABSTRACT
The concept of surface aggregation for surfactants was first introduced to explain abrupt changes in interfacial properties as a function of surfactant concentration. Gaudin and Fuerstenau [1] inferred the existence of surface aggregates from zeta potential measurements, which showed an increase in the gradient of surfactant adsorption at a particular concentration. This concentration was approximately a constant fraction of the critical micelle concentration (cmc), which suggested that the surface process was similar to bulk micellization [2]. Unlike simple monovalent ions, surfactant ions reversed the charge of solids even when they were not lattice ions. This ad-sorption against an electrostatic potential implied that the surfactants attracted each other. In early work, the attractive force was assumed to be van der Waals interactions, but later it was attributed to the hydrophobic effect. The surface density and wetting properties of the surfactant
clusters were consistent with the surfactant adopting an orientation with the alkyl chains facing the solution. These small clusters were called “hemimicelles.” Later, surface aggregates were proposed in a number of different systems and new names such as “admicelles” [3], surface micelles, and “solloids” [4] were proposed.
