Polymer-Grafted Nanoparticle Membranes with Unprecedented Gas-Separation Performance

Recent work has shown that nanoparticles grafted with polymer chains (GNPs) possess unusual collective properties. Their gas permeability shows non-monotonic behavior with increasing polymer length, with peak permeability increases of 8-20 times relative to the neat polymer. Similarly, their mechanical properties change from brittle to tough around the chain length with peak gas permeability. We show by combining small angle x-ray scattering, x-ray photon correlation spectroscopy and linear rheology that this behavior reflects the transition of the GNP materials from a jammed, soft glass-like state to liquid-like behavior with increasing chain length. For chain lengths below this transition, polymers on adjacent nanoparticles do not interpenetrate. Polymer melt incompressibility then results in a system where the coronas distort so that they tile space yielding a jammed (disordered) colloidal state. At longer chain lengths, this colloidal behavior disappears because chains on adjacent coronas interpenetrate. Since the dynamic properties of these systems, spanning time scale from the ps to the macroscopic, are affected by this transition we postulate that all of their transport properties should show anomalous behavior.