Dynamic surface tension studies on poly(N-vinylcaprolactam/N-vinylpyrrolidone/N,N-dimethylaminoethyl methacrylate) at the air–liquid interface

The adsorption of poly(N-vinylcaprolactam/N-vinylpyrrolidone/N,N-dimethylaminoethyl methacrylate), a commercial product with the trade name of Gaffix® VC-713 and currently used as a kinetic inhibitor for natural gas hydrates, has been experimentally studied at the air–liquid interface using surface tension measurements. The influence of polymer concentration and temperature on the adsorption of the polymer was analysed. The equilibrium experimental data obtained at both 293 K and 278 K has been fitted using the analogous surface equation of state for the Langmuir isotherm. Dynamic adsorption has been modelled using both diffusion-controlled and asymptotic models. The values of the surface tension and the surface excess at saturation showed that the polymer was very active at the air–liquid interface. Equilibrium surface tension indicated that temperature has a weak influence on the number of moles of Gaffix® VC-713 adsorbed on the interface. The dynamic adsorption was controlled by diffusion process initially, in which a rapid reduction in surface tension was observed. It was then followed by a slow polymer reorganization process. A strong dependence of the dynamic adsorption on both the temperature and the polymer concentrations was well demonstrated.