129 Xe NMR of xenon trapped in fully dehydrated mesoporous silica

129Xe NMR spectra of natural abundant xenon gas trapped in fully dehydrated mesoporous materials with pore sizes smaller than 2 nm in diameter were observed under atmospheric pressure in the temperature range between 168 and 373 K. The average pore diameters of the materials studied in this paper were 0.5, 1 and about 2 nm for molecular sieves 5A and 13X and synthesized mesoporous silica, respectively. The samples were fully dehydrated using an ultra-high vacuum (UHV) system and xenon gas was introduced with the sample pre-cooled to 168 K just above the boiling point of xenon. The 129Xe NMR spectra were observed as a function of increasing temperature and the 129Xe shift were observed at each temperature for the three samples under atmospheric pressure. The behaviors of xenon atoms in small pores observed in equilibrium states can provide important information on relationships between the pore structure and 129Xe chemical shift

A new type of sample tube for reducing convection effects in PGSE-NMR measurements of self-diffusion coefficients of liquid samples

Pulsed gradient spin-echo (PGSE) NMR measurements of the self-diffusion coefficients of low viscosity liquids are greatly hampered by the effects of convection especially away from ambient temperature. Here we report on a new NMR tube designed to minimize the deleterious effects of convection. In this tube, which derives from a Shigemi symmetrical NMR tube, the sample is contained in an annulus formed from a concentric cylinder of susceptibility matched glass. The performance of this tube was demonstrated by conducting measurements on the electrochemically important LiN(SO₃CF₃)₂ (LiTFSI)–diglyme (DG) system. Calibrations were first made using DG at column heights of 2, 3, and 4-mm in the temperature range between −40 and 100 °C. Measurements of the diffusion coefficients of the lithium, anion, and DG were then performed to probe the solvent–ion and ion–ion interactions in the DG doped with LiTFSI. Changes in the ¹H, ⁷Li, and ¹⁹F PGSE-NMR attenuation curves at −40 °C provided clear evidence of interactions between the DG and lithium ion

NMR studies of nanoscale organization and dynamics in polymer electrolytes

Multinuclear (i.e., 7Li, 19F, and 1H) NMR relaxation and pulsed field gradient spin-echo (PGSE) NMR translational diffusion measurements have been used to study the reorientational and translational dynamics of the polymeric, anionic, and cationic species in a polymer electrolyte system composed of high-molecular-weight comb-branched polyethers and their precursor macromonomers of cross-linked random copolymers, with and without LiN(SO2CF3)2 (LiTFSI) doping. The macromonomers are derivatives of glycerol bonded to ethylene oxide-co-propylene oxide (m(EO-PO)) and are viscous liquids with a molecular weight of approximately 8000. The results were consistent with a picture of the lithium ions undergoing local motions near the polymer chains, whereas the anions diffuse through a slowly fluctuating three-dimensional porous polymer matrix. Four years later, the macromonomer electrolyte samples were re-measured to investigate the effects of long-term aging. The NMR data revealed that the electrolyte has undergone sigficant structural relaxation. The findings shed light on the evolving molecular architectures that influence conductivity and help to explain the non-ideal conductivity behaviour

Ion diffusion restricted by time-dependent barriers in a viscous polyethylene-based liquid electrolyte

Polymer-electrolytes for use in lithium rechargeable batteries have the potential ability to power portable devices, yet the molecular level details of the ionic conduction mechanisms, which lie at the crux of their functionality, are poorly understood. Standard electrochemical theories fail to predict both the time dependence of the ionic conductivity and its correlation with the nature and time dependence of the diffusion coefficients of the individual species (i.e. anion, cation, and polymer) in such electrolytes. Consequently, the development of high-performance polymer-electrolyte batteries is hindered