Aggregation states of polystyrene at nonsolvent interfaces

The aggregation states of polystyrene (PS) thin films at interfaces with nonsolvents 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 for the film in hexane exhibiting a diffuse interfacial layer due to swelling. Also, the local conformation of PS in the outermost region of the films was quite sensitive to the surrounding environment and consequently responded to a change in its environment. This was the case for typical nonsolvents such as water and methanol. The extent of the conformational change might be explained in terms of the interfacial energy.