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A Brief Survey of $\beta$-Detected NMR of Implanted 8 Li + in Organic Polymers

TitleA Brief Survey of $\beta$-Detected NMR of Implanted 8 Li + in Organic Polymers
Publication TypeJournal Article
Year of Publication2014
AuthorsMcGee, FH, McKenzie, I, Buck, T, Daley, CR, Forrest, JA, Harada, M, Kiefl, RF, Levy, CDP, Morris, GD, Pearson, MR, Sugiyama, J, Wang, D, MacFarlane, WA
JournalJ. Phys.: Conf. Ser.

Unlike the positive muon, we expect the chemistry of the implanted 8 Li + 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 of 8 Li + 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/ T 1 . There is very little dependence of either linewidth or 1/ T 1 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 Al 2 O 3 , and suggests that 8 Li + 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.