Polymer/Liquid Interface

Abstract

As stated in the previous review by Kawaguchi and Matsushita, neutron reflectometry (NR) enables us to gain direct access to density or composition profile along the direction normal to the surface with an excellent depth resolution being better than 1 nm. We here show our recent results dealing with density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane and methanol, which are typical “non-solvents” for dPMMA. The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by atomic force microscopy (AFM). The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film.