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.