ADSORPTION OF CATIONIC SURFACTANTS AT THE AIR-WATER-INTERFACE - A KINETIC-STUDY BY MEANS OF A CAPILLARY WAVE METHOD

The damping coefficient and the wavelength of ripples on the surface o f aqueous solutions of dodecylammonium chloride (DAC) and cetyltrimeth ylammonium chloride (CTAC) have been measured as a function of frequen cy and surfactant concentration. For DAC solutions, experimental resul ts are in agreement with the theory of capillary waves if the model of a diffusion-controlled adsorption process is used as the basis of the theoretical description. It appears likely that CTAC follows a diffus ion-controlled adsorption mechanism also, but in this case the accurac y of the results is insufficient. For substances with high surface act ivity, the adsorption kinetics only influence slightly the dynamic sur face properties at low frequencies, and the CTAC film behaves as an al most insoluble monolayer during the surface wave propagation.