Gas Transport Properties of Polymer-Grafted Nanoparticles with Dense Polymer Brushes

Polymer-grafted nanoparticle (GNP) membranes have become increasingly relevant materials for efficient size-based separation of gas mixtures in industrial processes. Membranes composed of these grafted particles have demonstrated higher gas permeability and more tunable selectivities relative to the neat polymer systems. Previous experimental and computational work led to the development of a two-layer model, representing the grafted polymer around the nanoparticle as distinct dry and interpenetration layers. However, the role in gas transport that each layer has in this model is not well understood. In our work, we study the effect of increased graft density in the dry zone on poly(methyl acrylate)-grafted-silica nanoparticles via permeation and scattering techniques. Silica surface interactions, dry zone stretching, and interpenetrated chains all contribute to a greater understanding of the transport mechanism in these systems. We find that bimodal dense brushes impact the motion of disparate penetrant sizes to varying degrees, i.e. significantly depressing light gas transport while having a minimal effect on larger penetrants.