A Brief Survey of β-Detected NMR of Implanted 8Li+ in Organic Polymers

[摘要] Unlike the positive muon, we expect the chemistry of the implanted8Li+β-NMR probe in organic polymers to be simply that of the monovalent ion, but almost nothing is known about the NMR of isolated Li+ in this context. Here, we present a brief survey of8Li+β-NMR in a variety of insulating polymers at high magnetic field, including polyimide, PET, polycarbonate, polystyrene and polyethylene oxide. In all cases, we find a large-amplitude, broad Lorentzian resonance near the Larmor frequency, consistent with the expected diamagnetic charge state. We also find remarkably fast spin-lattice relaxation rates 1/T1. There is very little dependence of either linewidth or 1/T1 on the proton density, the main source of nuclear dipolar magnetic fields, leading us to conclude the main contribution to both broadening and spin relaxation at room temperature is quadrupolar in origin. This behaviour is very different from crystalline insulators such as MgO and Al2O3, and suggests that8Li+β-NMR will be an important probe of polymer dynamics. Additionally, we note dramatically different behaviour of one sample above its glass transition, motivating the construction of a high temperature spectrometer to enable further exploration at elevated temperature.

[发布机构] Department of Physics, University of British Columbia, Vancouver; BC; V6T 1Z1, Canada^1;TRIUMF, Vancouver; BC, Canada^2;Department of Chemistry, Simon Fraser University, Burnaby; BC; V5A 1S6, Canada^3;Department of Physics and Astronomy, University of Waterloo, Waterloo; ON; N2L 3G1, Canada^4;Toyota Central Research and Development Laboratories Inc., Nagakute, Aichi; 480-1192, Japan^5;Canadian Institute for Advanced Research, Canada^6;Chemistry Department, University of British Columbia, Vancouver; BC; V6T 1Z1, Canada^7

[关键词] Crystalline insulators;Dipolar magnetic fields;Elevated temperature;High magnetic fields;High temperature;Insulating polymer;Larmor frequencies;Spin lattice relaxation rates