DMREF:Collaborative Research: Designing Optimal Nanoparticle Shapes and Ligand Parameters for Polymer-Grafted Nanoparticle Membranes

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The project investigates a new class of polymer-grafted membranes that have the potential to improve gas separation characteristics for a wide range of applications in the environmental, energy, and chemical manufacturing areas. The polymer-grafted membranes consist of a matrix of inorganic nanoparticles with grafted polymer ligands that show improved separation characteristics compared to commonly used organic membranes. The project will use a combination of theoretical analysis, synthesis, and experimental evaluation to optimize both the nanoparticle shape and the polymer properties, while providing basic understanding of the mechanism by which the grafted structures improve separation efficiency. The project will also provide educational and outreach components including research opportunities for undergraduate students from Florida A&M University (a historically black college or university). While a key class of organic membranes is made of glassy polymers, they suffer from the fact that their permeability (i.e., product flux) and selectivity (i.e., purity of the desired species) are inversely correlated. Preliminary work using assemblies of inorganic nanoparticles (NPs) chemically grafted with polymer chains show that these materials offer unexpected advantages in this context. Based on simulations it is postulated that the self-assembly of the polymer grafted-NPs into ordered arrays creates "interstitial spaces" which can only be filled by stretching some of the grafted chains ("entropic frustration"). Placing solute molecules relieves this frustration and yields the improved separation ability. The study is predicated on the hypothesis that non-spherical nanoparticles may offer a separation advantage due to packing into meta-crystals that are stabilized by vacancies (of order 10%). Non-spherical NP-grafted polymers will be studied by (1) developing novel theoretical design tools to find the NP shapes and grafting parameters that optimize the permeability and selectivity of relevant gas mixtures; and (2) synthesizing polymer grafted non-spherical NPs, assembling them into membranes and characterizing their multi-scale structure and dynamics using a suite of tools including advanced scattering techniques (x-ray, neutron) coupled with theory. This should allow for the validation of the design results and help close the prediction-synthesis-characterization loop. This validated design software will be made freely available to the research community. In addition to the educational collaboration with Florida A&M University, the investigators will also recruit underrepresented students (both women and minorities) with the dual goals of placing Columbia University students into local industry and attracting industrial participants into higher degree and/or refresher programs at Columbia.