Self-assembly of Nanoparticles at Polymer Surfaces Induced by Supercritical Carbon Dioxide

The surface segregation (i.e., preferential segregation of one component to the surface in multicomponent systems) is common to all material classes and is typically driven by a reduction in surface energy which more than compensates for the entropy loss and/or energy gain associated with the demixing of the components. However, the conventional surface segregation requires high temperatures, typically close to 200$^{\circ}$C, and long annealing time, in order to ensure enough polymer mobility. Here we show a low-temperature and environmentally green method to preferentially migrate inorganic nanoparticles to the polymer surface regions using supercritical carbon dioxide near the critical point. In addition, the scCO$_{2}$-based surface segregation may be a general phenomenon regardless of a choice of nanoparticles and polymers. In this talk, we will discuss the mechanism and detailed characterization of the surface structures using scanning probe microscope, neutron/X-ray reflectivity, and X-ray photoelectron spectroscopy.