(384a) Diffusion Enhancements in Mineral Nanoparticle Filled Superglassy Polymers

Addition of nanoparticles to high free volume, stiff chain, glassy polymers can increase light gas (carbon dioxide, hydrogen, nitrogen, and methane) permeability with increasing particle loading. However, the degree and cause of the permeability enhancement greatly depends on particle surface chemistry, which influences both polymer-particle and penetrant-particle interactions. Polymer-particle interactions influence the maximum practical particle loading, (i.e., the greatest particle loading where the nanocomposite maintains a selectivity similar to that of the unfilled film), which can be as high as 75 volume percent nanoparticle in extreme instances. In this case, light gas diffusivity increases over an order of magnitude relative to that in the unfilled polymer. Such high loadings are obtained in systems where the nanoparticles chemically react with the polymer. In other polymer-particle composites, there is almost no chemical interaction. Such nanocomposites may still have excellent particle dispersion, but any changes in gas transport result from penetrant-particle interactions or in a physical modification (e.g., disruption of chain packing) of the polymer matrix.

Polymer-penetrant interactions have a strong influence on gas transport. In many cases, the nanocomposite permeability enhancement can be attributed, at least partially, to an enhancement in light gas solubility. Such behavior occurs when the nanoparticle gas adsorption properties are markedly different the gas solubility in the polymer. There are possibilities for reactions between the particle and penetrants as well. For example, water and/or carbon dioxide may react irreversibly with the particles, thereby reducing particle induced solubility enhancements.

The influence of mineral nanoparticle dispersion on permeability, diffusivity, and solubility in high free volume, stiff chained, glassy polymers has been characterized. Particle dispersion has been observed using tapping mode atomic force microscopy. Polymer-particle and penetrant-particle reactions have been documented using proton and carbon NMR, as well as FTIR and WAXD. These experiments combine to show the complexity and versatility of mineral filled nanocomposite materials.