(5ad) Surfactant Adsorption at Fluid Interfaces

Surfactants (surface active agents) are amphipathic compounds with a hydrophilic head group and a hydrophobic tail, and are to some degree soluble in both aqueous and organic solvents. Surface activity implies the preferential concentration of surfactant molecules in the surface or interfacial region over that of the bulk solution. The adsorption of surfactants at fluid interfaces decreases the interfacial tension and is integral to many processes, including, but not limited to, detergency, wetting, foaming and defoaming, emulsification, and drug delivery.

The adsorption characteristics of surfactant mixtures are not simple averages of those of the constitutive components. However, even many single component surfactant systems remain poorly characterized due to the often unknown presence of highly surface active trace contaminants. There is generally a substantial difference observed in the adsorption dynamics and equilibria of surfactants used ?as-received? verses those of grade ?surface-chemically pure?. The thermodynamic properties fundamental to the description of surfactant adsorption can only be determined when the measured surface tension is a true reflection of only the surfactant of interest.

In practice, surfactants are utilized as multi-component mixtures. Of particular interest is the behavior of certain bio-surfactants contained within the thin liquid layer lining of the lung alveoli. There is strong clinical evidence that pulmonary surfactant is vital for correct lung function. Understanding of how the different components of pulmonary surfactant contribute to the rapid adsorption as well as to the ability of the pulmonary surfactant to remain at the air/water interface during the breathing cycle is crucial to the design of surfactant replacement therapies.