Adsorption Kinetics of a Cationic Surfactant Bearing a Two-Charged Head at the Air-Water Interface

FERNÁNDEZ LEYES, MARCOS; GIMENEZ REYES, SANTIAGO; CUENCA, EZEQUIEL; SÁNCHEZ MORALES, JHON F.; RITACCO, HERNÁN

Coatings

MDPI

Lugar: Basel; Año: 2020 vol. 10

We studied the dynamics of adsorption at the air-water interface of a cationic surfactantbearing two charges, Gemini 12-2-12, at concentrations below and above the critical micelleconcentration (cmc). We used maximum bubble pressure and Wilhelmy plate techniques in order toaccess all time scales in the adsorption process. We found that the adsorption dynamics are controlledby diusion at the initial stage of the adsorption process (milliseconds) and it is kinetically controlledby an electrostatic barrier (minute) approaching the equilibrium surfactant surface concentration.Between these two extremes, we found several relaxation phenomena, all following exponentialdecays with characteristic times spanning from one to hundreds of seconds. By means of time-resolvedsurface potential measurements, we show that these processes involve charge redistribution withinthe interfacial region. The surface tension data are analyzed and interpreted in the framework of thefree energy approach.