Self-Organization of PS-b-PFOMA Block Copolymer Aggregates in Thin Films

SFM, STEM and XPS were employed to study the morphologies of polystyrene-b-poly(1,1',2,2'-tetrahydroperflurooctyl methacrylate) (PS-b-PFOMA) films. The copolymer was dissolved in the co-solvent mixture of Freon 113 and toluene. Upon spin-casting on Si/SiOx substrate, PS-b-PFOMA was found to self-organize into spherical aggregates, where the cores of the spheres were composed primarily of PFOMA and the matrix was composed by PS. However, exposing the films to supercritical CO$_{2}$ led to a reversed morphology, where spheres of PS were embedded in the matrix of PFOMA. In addition, the degree of ordering was improved in sc-CO$_{2}$ and the domain size was tuned by adjusting sc-CO$_{2}$ density. The results were discussed based on the effects of sc-CO$_{2}$ on the interfacial tension and the relative PS-PFOMA interactions.