Structural and Molecular Transport Properties of Self-Assembled polymer grafted Nanoparticles

The use of polymer-grafted nanoparticles (NPs) for dispersing nanofiller in a polymer matrix has led to novel materials exhibiting improved mechanical and optical properties, though their applicability to molecular transport has remained unexplored. We focus here on spherical silica NPs (d=14nm) sparsely grafted with polystyrene (PS) chains in a PS matrix. By tuning the graft density and PS chain lengths, a variety of self-assembled structures can be formed and characterized through TEM imaging and Small-Angle X-ray Scattering (SAXS). The gas transport performance of the various hybrid materials, measured via Quartz Crystal Microbalance (QCM) and steady-state permeation experiments, show that the CO₂ permeabilities do not obey conventional (i.e., Maxwell) theories for transport (despite the pure grafted NPs following prediction) and that the spatial distribution of the NPs in the self-assembled state has profound consequences on molecular transport properties. Additionally, high frequency mechanical measurements permitted by the QCM indicate variations in mechanical performance in these materials. The ability to rationally design polymer composites with tunable transport properties using NP morphological control thus represents a new path forward for advanced membrane design