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.