Adsorption of catanionic surfactants at air/solution interface.

The adsorption of symmetric and asymmetric chain catanionic surfactants was investigated by surface tension measurement. The dynamic and equilibrium s urface properties can be well interpreted in terms of a two-dimensional pha se transition between a gas and condensed state of the adsorbed layer. The hydrophobic driving force as well as the increasing ionic strength of the m edium in the case of asymmetric alkyl chains make the 2D phase transition u nfavourable. A molecular interaction model was developed to describe the quasi-neutral a dsorption and the two dimensional phase properties of the catanionics. The prediction of the model is in a good agreement with the observed surface ch aracteristics of the investigated catanionic surfactants.