(241c) Permeability Enhancement in Nanoparticle Filled Polymeric Membranes
A developing area of research for membrane materials is the addition of nanoparticles to high free volume, stiff chain glassy polymers. Such nanocomposites have higher permeability and diffusivity than the corresponding unfilled polymer. Changes in gas transport properties have been attributed to the disruption in polymer chain packing caused by the inclusion of nanoparticles in the polymer matrix. Since the polymers chains are very stiff, they are insufficiently mobile to compensate for disruptions in packing over molecular distances, which cause the nanocomposite free volume to increase with increasing particle loading. Consequently, both diffusivity and permeability increase with increasing particle loading. Due to chain mobility arguments, this technique for increasing permeability has been traditionally been limited to a small family of rigid glassy polymers.
Recently, a new nanocomposite family has been discovered utilizing rubbery polymers as the matrix. Like the stiff chain polymers, light gas (i.e., carbon dioxide, hydrogen, nitrogen, and methane) permeability and diffusivity increase with increasing particle loading, (e.g., carbon dioxide permeability in 1,2-polybutadiene filled with 34 volume percent MgO is 2600 % higher than the unfilled polymer). The change in permeability and diffusivity depend on particle dispersion, which is closely related to particle-polymer interactions. However, depending on particle surface chemistry and penetrant-particle interactions, penetrant solubility may also be enhanced. These studies have focused on both polar (i.e., crosslinked poly(ethylene glycol) diacrylate) and non-polar (i.e., 1,2-polubutadiene) polymers, as well as a series of particles (i.e., MgO, TiO2, SiO2). These materials have been characterized using light gas sorption and permeation to monitor gas transport properties as well as AFM and X-ray microtomography to characterize particle distribution within the polymer matrix.
 T. C. Merkel, B. D. Freeman, R. J. Spontak, Z. He, I. Pinnau, P. Meakin and A. J. Hill, Ultrapermeable, Reverse-Selective Nanocomposite Membranes, Science, 296 (2002) 519-522.