PROBING THE STRUCTURE OF THE ADSORPTION LAYER OF SOLUBLE AMPHIPHILIC MOLECULES AT THE AIR-WATER-INTERFACE

Optical second harmonic generation (SHG) together with surface tension measurements are used to investigate soluble amphiphilic molecules adsorbed at the air/water interface from solution. It is found that the adsorbed molecules form a single polar-oriented monolayer which, at saturation, resembles a close-packed monolayer of insoluble molecules. SHG is particularly sensitive to the noninversion symmetry of the interfacial region and therefore provides an inherent discrimination against isotropically oriented molecules in the subsurface and the solution.