Solvent induced nanostructure formation in polymer thin films: The impact of oxidation and solvent

Polystyrene (PS) films, upon deep UV exposure, readily formed nanostructures when soaking in a solvent. In this study, we provide compelling evidence confirming the critical roles of oxidation and solvent for the nanostructure formation. When the irradiation was carried out in argon, no structure could be generated on the films. Solvent is another critical parameter. Ordered concentric circular structures formed when the UV-irradiated PS films were soaked in an aromatic solvent such as toluene, benzene, and xylene. Addition of n-heptane to toluene reduced the size of the circles. The concentric circular structures disappeared when 0.1% methanol was added to the soaking solvent toluene. X-ray photoelectron spectroscopy (XPS) showed that the percentage of O-containing products decreased with increasing amount of added methanol, indicating that the polar solvent prevented the structure formation by removing the oxidation products from the films.