SURFACTANT AGGREGATION AND MICELLIZATION STUDIED BY INTERFACIAL-TENSION AND OPTICAL 2ND-HARMONIC GENERATION

The adsorption of a nonionic amphiphile at the solution/air interface has been studied by surface second-harmonic generation. The bulk phase transition of micellization was observed by monitoring the surface-re flected nonlinear signal. The concentration dependence of the second-h armonic signal could be described in terms of a Langmuir isotherm allo wing the determination of the free energy of adsorption of the nonioni c molecules at the surface. A comparison with experimental data obtain ed from surface tension measurements suggests a depth-dependent distri bution of the surfactant molecules rather than a monolayer-type surfac e coverage.