Phase Behavior of Polymer-Grafted Nanoparticles Blends Thin Film Induced by Solvent Annealing and Thermal Annealing

The grafting of polymer chains to nanoparticles has been found as an important method to control the particle assembly structures on a thin film state. We hypothesized that polymer-grafted nanoparticles blends have similar upper or lower critical solution temperature type phase behavior corresponding to linear polymer blends if the degree of polymerization is larger enough. UCST system we take is poly (methyl methacrylate) silica (PMMA-SiO2) and poly(styrene) silica (PS-SiO2), LCST system we take is PMMA-SiO2 and poly(styrene)-(acrylonitrile) silica (PSANSiO2). Direct immersion annealing (DIA) method was used in switching the state of phase-separated structures in a binary blend film of UCST system, and thermal annealing method was used for the LCST system. Our results show that by varying the composition of the DIA solution, interchangeable phase separation state and homogeneous state are formed in the PMMA-SiO2/PS-SiO2 blends thin film within 1 minute. The phase reversibility of UCST system is stable. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) reveals that the switchable phase separation state for UCST system occurs all throughout the film. However, for LCST system, phase reversibility is not feasible. We hypothesized a layered structure may formed underneath the surface of the thin film for this phenomenon. We believe that the phase reversibility of PGNPs blends will play an important role in the future nanoparticle-based material science and engineering.