Creating Novel Gas Separation Constructs by Manipulating Free-Volume Distributions in Polymer-Grafted Nanoparticles

This research advances the understanding of a new class of membranes, polymer-grafted nanoparticles (GNPs), which are mixed matrix membranes with the added constraint that the chains are chemically tethered to the nanoparticles by one end. Pure GNP membranes yield large increases in gas permeability relative to the corresponding mixed matrix membrane that is untethered. It is postulated that the grafting process creates a material with a controllable sieve size. The objective is to characterize this sieve size, through a combination of a suite of experimental probes with analytical theory and computer simulations. The overarching goal is to develop models that will enable quantitative design variations in NP core size, graft parameters, and free polymer parameters to vary predictably the gas permeability and selectivity through GNP membranes.

Furthermore, the addition of free (ungrafted) chains of the same chemistry as the grafted chains allows further manipulation of the sieve effect. Added chains, in some cases, preferentially hinder large solutes, and yield extraordinarily large ideal selectivities. These results can be rationalized if, in addition to having increased sieve size, these GNPs are heterogeneous transport media. Accordingly, it is conjectured that the large gases go through the junctions between the NPs, while the smaller gases more uniformly permeate through the whole polymer. The second objective is to characterize and achieve means to control these heterogeneous sieve size distributions.