ABSTRACT
The hydrophilic moiety is attached to the backbone by an alkyl chain with different numbers of CH2 groups, and the hydrophilic groups can be attached to the dimethylsiloxane units at any position and/or to the terminal siloxane units. The hydrophilic groups can be replaced by purely hydrophobic alkyl or perfluoroalkyl groups, which lead to completely hydrophobic siloxane surfactants that show surface activity in nonpolar solvents. Siloxane surfactants usually have a high thermal stability and a strong surface activity. Furthermore they are nontoxic and do not irritate the skin. They are thus suitable for pharmaceutical and cosmetic applications. To characterize the surface activity of surfactants, M. J. Rosen introduced the expressions “efficient” and “effective.” The constitution of the hydrophilic group does not seem to affect the aggregation behavior of the siloxane surfactants. Ionic, zwitterionic, and nonionic siloxane surfactants can form both smaller and larger aggregates.
