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Direct Nano-Flux and Thermomechanical Analysis of Gas Separation Nanocomposite Membranes

Jason P. Killgore and Rene M. Overney. Chemical Engineering, University of Washington, Box 351750, Seattle, WA 98195

Modern separation technology is increasingly demanding of processes that use less energy and are less harmful to the environment. In contrast to conventional distillation, membrane technology addresses this need by placing less reliance on expensive and environmentally damaging techniques. A particularly attractive membrane material is poly[1-(trimethylsilyl)-1-propyne] (PTMSP) because it exhibits high permeability and reverse selectivity. These unique transport properties have been attributed to the extremely high free volume of the polymer. It has been demonstrated that both permeability and selectivity can be further enhanced, very likely due to effects at the polymer-inorganic interface, by the addition of nanoscale silica particles. However, direct observations of interfacial properties are still waiting to be explored. Recent developments in scanning force microscopy (SFM) provide the means to investigate, on the nanometer scale, flux properties directly on the membrane surface in conjunction with the local relaxation properties in the material. In this paper, we employ three of these local methods; i.e., shear modulation force microscopy (SM-FM), thermomechanical SFM (TM-SFM) and flux lateral force microscopy (F-LFM) to investigate the local transport and material properties of PTMSP in the vicinity of matrix embedded silica nanoparticles. With SM-FM and TM-SFM, local transition properties and heat fluxes are determined as functions of the radial distance from silica nanoparticles. The radial relaxation profiles are compared to local permeation fluxes obtained by F-LFM. Polymer chain mobility was found to influence the local permeability properties of the membranes. This study illustrates the impact of interfacial constraints on the flux properties of PTMSP; a polymer system that shows great potential for hydrogen separation.

J. H. Wei, M. He, R. M. Overney, Direct Measurement of Nanofluxes and Structural Relaxations of Perfluorinated Ionomer Membranes by Scanning Probe Microscopy, J. Membr. Sci., in press (2006)

Scott Sills, Hanson Fong, Cynthia Buenviaje, Mehmet Sarikaya, and René M. Overney, Thermal transition measurements of polymer thin films by modulated nano-indentation, J. Appl. Phys. (2005) 98 014302 (2005).

S. Sills, J. Frommer, Wilson Chau, Victor Lee, Bob Miller, Craig Hawker, R.M. Overney, Interfacial Glass Transition Profiles in Ultrathin Spin Cast Homopolymer and Crosslinked Polystyrene Films, J. Chem. Phys., 120 , 5334-8 (2004)