Adsorption kinetics of 1-octanol at the air-water interface

The adsorption of 1-octanol at an air-water interface is studied theoretically and experimentally. A video-enhanced pendant bubble tensiometry is utilized for the measurement of relaxation of surface tension. Two types of processes were investigated: the adsorption onto an initially clean air-water interface and the desorption out of a suddenly compressed interface which is originally at equilibrium. A theoretical simulation using the equilibrium surface tension is performed and it is concluded that there is no shift. in controlling mechanism for the adsorption of 1-octanol molecules from an aqueous phase onto an initially clean air-water surface. The adsorption of 1-octanol onto a clean air-water interface is verified experimentally to be a diffusion-controlled process. A diffusion coefficient was computed by comparing these adsorption profiles with numerical solutions of bulk surfactant diffusion equation and the generalized Frumkin adsorption model. The re-equilibration of a compressed interface agrees well with a diffusion-controlled process. Lower bounds on the kinetic constants for the sorption process are inferred for octanol by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the desorption relaxation data.