Exploring Macroscopic Manifestations of Microscopic Gas Transport Pathways in Polymer-grafted Nanoparticle Membranes

Polymer nanocomposites have become increasingly relevant materials for use as efficient gas separation membranes in industrial processes. "Matrix-free" polymer-grafted nanoparticles, where all available polymer in the system is chemically tethered to the particle surface, have been explored in this context to overcome difficulties controlling nanoparticle dispersion. Membranes composed of these grafted particles have demonstrated remarkable enhancements in gas transport over that of neat polymer systems, where the degree of enhancement is greater for larger penetrant sizes. Techniques measuring macroscopic properties, such as permeability and activation energy, grant us insight into the microscopic gas transport mechanisms in these systems. These materials have been shown to be spatially heterogeneous, comprised of low-density interstitial regions, and areas of high polymer density close to the particle surface. This work aims to explore the relationship between observable macroscopic properties and proposed mechanisms for penetrant transport in these systems. The effects of preparation methods, penetrant size, and underlying structural formation are key to understanding such enhancements.