Entropy-Driven Phase Separation in Polymer-Grafted Nanoparticle Blends Thin Film

Polymer-grafted nanoparticle (PGNP) blends exhibit versatile properties ranging from optoelectronics to gas separation membranes, primarily governed by the composition, morphology, and mobility of the polymers and nanoparticles involved. This study investigates the phase behavior of chemically dissimilar polymer grafted nanoparticle blends, specifically PMMA-SiO2/PSAN-SiO2, and compares them with their linear polymer counterparts, PMMA/PSAN, under similar conditions. We have meticulously examined the phase separation and mixing behavior of these blends under vacuum thermal annealing (VTA). Our findings indicate that grafted polymer blends with specific weight fractions tend to exhibit phase separation, whereas linear polymer blends favor mixing. This phenomenon is attributed to the higher entropy of mixing in linear polymers compared to grafted polymers, despite both systems sharing identical enthalpic interactions. The study further reveals that high molecular mass PGNPs promote mixing instead of phase separation. This behavior can be explained by the longer chain lengths attached to the particles, which influence the overall morphology and interaction dynamics within the blend. Additionally, variations in weight fractions significantly affect the mixing and demixing tendencies, depending on the molecular masses of the blends. We employed Atomic Force Microscopy (AFM) to prob the surface morphology of the thin films, providing detailed insights into the topographical features and phase distribution. To further analyze the internal structure of the films, we utilized Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). This technique enabled us to obtain depth profiles and compositional maps, shedding light on the distribution of different film components. The TOF-SIMS analysis corroborated the AFM findings, comprehensively understanding the phase behavior in PGNP and linear polymer blends. In addition to AFM and TOF-SIMS, we also employed X-ray Photoelectron Spectroscopy (XPS) to analyze the surface chemistry and composition of the blends. The findings of all these techniques will be presented.