Aggregation states of polymers at non-solvent interfaces by neutron reflectivity

The aggregation states of polystyrene (PS) thin films at interfaces with non-solvents such as water, methanol and hexane were examined by specular neutron reflectivity and sum-frequency generation vibrational spectroscopy. The density profiles of the PS thin films along the direction normal to the interface with water and methanol were comparable to that in air. However, this was not the case of the film in hexane exhibiting a diffused interfacial layer due to swelling. Also, the local conformation of PS at the outermost region of the films was quite sensitive to the surrounding environment and responded consequently to a change in its environment. This was the case for typical non-solvents such as water and methanol. The extent of the conformational change might be explained in terms of the interfacial energy. Similar experiments are also performed for poly(methyl methacrylate) (PMMA). Results so obtained are compared with each other.