Gas Sorption into Surface of Poly(methyl methacrylate) Films at Atmospheric Pressure

Interfacial structure of deuterated poly(methyl methacrylate) (dPMMA) and polystyrene (dPS) films with gases such as carbon dioxide (CO2) and nitrogen (N2) under a pressure of 0.1 MPa was examined by neutron reflectivity (NR). The interface was analyzed using a model that the density of the outermost region of the films was lower than that of the interior region. The density profile was expressed by a single exponential equation with a decay length (ξ). The ξ values for the dPMMA films under CO2 and N2 were larger than that under vacuum at a given temperature, and the extent was more remarkable under CO2 than under N2. On the other hand, such a gas sorption was not clearly discerned for the dPS films. Finally, the surface relaxation in the dPMMA and dPS films under CO2 and N2 was discussed on the basis of lateral force measurements.