Kinetically Arrested Blend Phase Separation Through Interfacial Nanoparticle Jamming

Immiscible binary polymer blends undergo phase separation via spinodal decomposition or nucleation and growth depending on quench depth. We report different regimes of spinodal phase separation in dynamically asymmetric polystyrene/poly(vinyl methyl ether) blends with polystyrene grafted nanoparticles (GNPs) using in-situ atomic force microscopy, scanning electron microscopy, and x-ray photon correlation spectroscopy. The study employs a thin film of PS mixed with GNPs, sandwiched between a silicon wafer and a PVME thin film. For highly grafted GNPs, expected to be well-dispersed in the PS phase, phase separation evolves similarly to the neat blend, as GNPs are not interfacially active. In contrast, GNPs with lower graft density progressively localize at the interface with increased loading in the PS phase. This controlled GNP localization leads to a systematic arrest of phase separation, significantly reducing pattern size. To the best of our knowledge, this is the first experimental report demonstrating correlated interfacial NP jamming and kinetically arrested phase separation, with potential applications in Pickering-like emulsions and bijels.