Adsorption kinetics of ammonium perfluorononanoate at the air-water interface

The adsorption of the fluorocarbon surfactant, ammonium perfluorononanoate (APFN) has been studied in an overflowing cylinder (OFC). The equilibrium adsorption isotherm, determined by drop shape tensiometry, is well-described by the Volmer isotherm. The dynamic surface excess at the-expanding surface of the OFC was measured by neutron reflectometry (NR). The dynamic surface excess was in good agreement with the predictions of a diffusion-controlled adsorption model. Significant Marangoni effects were observed. The relationship between the mass transport equation in the OFC and the short and long-time asymptotes of the Ward-Tordai equation is noted.