Additional Support for a Revised Gibbs Analysis

Gibbs-determined areas of >60 angstrom(2)/molecule for many common surfactants cause rather small surface tension reductions when measured on a Langmuir Film balance. This is inconsistent with ail air/water interface being saturated throughout the steep linear decline in plots of surface tension versus In [surfactant]. In support for a gradually populating interface in the linear re,ion, we have found that sodium docosanyl sulfate lowers the surface tension by only 7 mN/m when compressed to 50 angstrom(2)/molecule. When docosanyltrimnethylmmonium bromide is compressed to 65 angstrom(2)/molecule, the surface tension is lowered about 15 mN/m as compared to a 30-40 mN/m drop occurring within the range of typical Gibbs analysis. Saturation of the interface is often obscured by competitive micelle formation that levels the surface tension versus in [surfactant] plot before saturation has it chance to do so.