NMR studies on supercritical fluids in nanoporous materials

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¹²⁹Xe NMR spectroscopy is applied to investigate the physical properties of Xe confined in porous glasses up to the supercritical region. The chemical shift of confined Xe is larger than that of bulk Xe, which is approximately proportional to density, and the upward deviation is more enhanced for smaller pore. The deviation is large in the gas phase, and has a maximum far below the critical density, while it gradually decreases and approaches zero in the liquid phase. Below the critical density the both of the size and surface effects are observed, while the surface effect becomes minor and the size effect persists above the critical density. The chemical shift at the dilute limit depends on the surface properties of the matrix, as well as the pore size. [DOI: 10.1380/ejssnt.2005.338]