Understanding Gas Transport in Polymer-grafted Nanoparticle Membranes*

Polymer nanocomposites have become increasingly useful materials for a diverse set of applications, including as industrial gas transport membranes for separations processes. Difficulty controlling nanoparticle dispersion in these nanocomposites has led to the use of polymer-grafted nanoparticles in a “matrix-free” configuration, where all polymer present in the system is chemically tethered to the surface of the nanoparticles. Materials composed from these grafted particles have been shown to display a remarkable enhancement in the gas transport properties of these systems. It has been proposed that the activation energy for penetrant motion through a polymeric membrane scales as the square of penetrant kinetic diameter, and can be related to a material-dependent critical size parameter. This work investigates macroscopic manifestations of this microscopic gas transport mechanism in grafted nanoparticle systems.