Polymer membranes are employed in several critical sustainability applications involving the separation of gas mixtures based on size differences. In spite of their widespread use, important performance challenges remain outstanding - the need to dramatically affect the transport of a desired mixture component and improving mechanical resilience relative to the current state-of-the-art. Here, we develop novel membranes based on polymer-grafted nanoparticles (GNPs) which possess controllable, spatially inhomogeneous gas transport behavior. We show that smaller gases are transported more uniformly than larger solutes in the polymer layer of pure GNPs; these larger gases preferentially move through the interstices between the NPs. Free chains added to these GNPs preferentially segregate into these interstices where they selectively hinder large solute motion and thus yield dramatic performance improvements for several industrially relevant gas pairs. The magnitude of these effects are controlled by grafting parameters and the length of the free chains. Our ability to create and tune spatial inhomogeneities in GNPs, apparently through judicious manipulation of chain entropy, is thus a new, apparently general, physics-based paradigm to design membranes with unprecedented performance even using common polymers.
Professor Kumar received a BTech in chemical engineering from the Indian Institute of Technology, Madras in 1981 and a ScD in chemical engineering from the Massachusetts Institute of Technology in 1987. He joined the faculty of Columbia Engineering in 2006. His group has been the pioneer over the last decade in the practically relevant topic of Polymer Nanocomposites where inorganic nanoparticles are added to polymers to obtain materials with synergistic properties. A central problem in this area is that the inorganic, hydrophilic nanoparticles are frequently immiscible (organic) polymers – thus the promised property improvements from these materials have remained hard to realize. His work in this area spans all topics of polymer nanocomposites including self-assembly, microstructure, glassy segmental dynamics and vitrification, elasticity and reinforcement, linear and nonlinear mechanical-dynamical phenomena (such as strain softening and yielding), chain relaxation, and nanoparticle diffusion and dynamics.