On self-diffusion in plastic crystals

Abstract

Self-diffusion parameters for plastic molecular crystals are obtained by re-analysing nuclear magnetic resonance relaxation data using the theoretical treatment due to Wolf. This takes into account the correlated nature of the molecular motion. Using a model for vacancy induced motion previous anomalies in the N.M.R. interpretation are reduced and the parameters obtained using the various N.M.R. techniques are consistent for all plastic crystals studied. By taking account of the effects of correlated motion self-diffusion coefficients are calculated whose magnitude is generally in excellent agreement with those obtained by the radio-tracer technique, although some anomalies still exist. The improved agreement between different sources of experimental data demonstrates the existence of correlated molecular motion that arises, for example, with a vacancy-induced diffusion mechanism.

Proton NMR and Dynamic Studies of Hydrous Ruthenium Oxide

“…We have used solid-state 1 H NMR spectroscopy to study the proton dynamics of hydrous ruthenium oxides (RuO 2 · x H 2 O) annealed at different temperatures. To our knowledge, this is the first comprehensive study on the proton dynamics of these technologically important materials, although NMR spectroscopy has been widely used in ionic conducting materials. − Here, we experimentally obtained the activation energy ( E a ) of the RuO 2 · x H 2 O samples from the variable-temperature 1 H spin−lattice relaxation time ( T 1 ) measurements. Our results show that the activation energy is rather low for the RuO 2 · x H 2 O samples annealed in the temperature range of 116−175 °C but relatively high for those annealed below 100 °C and above 200 °C, which is highly consistent with the specific capacitance measurements.…”

Dynamics of Dimethylbutanols in Plastic Crystalline Phases by Field Cycling 1H NMR Relaxometry

“…Considering the molecular structure of the investigated alcohols (Figure ) and the phases they form in the examined temperature range, contributions arising from internal motions ( R 1 IM ) and overall molecular reorientations ( R 1 MR ) were expected in all phases. On the other hand, translational self-diffusion ( R 1 SD ) certainly contributes to relaxation in the liquid phase, as already pointed out in a previous study, but it might also affect relaxation in the ODIC phases, as reported in the literature for other plastic crystals. − ,,, …”

“…For all samples, the D values determined in the liquid and crystalline phases (Figure 7) were on the same order of magnitude of those determined for other plastic crystals in the corresponding phases. 3,[6][7][8][9][10][11][12]69 D showed decreasing trends by decreasing the temperature in each phase, whereas discontinuities were observed at melting for 2,2-DM-1-B and 3,3-DM-1-B and at the Cr1 to Cr2 transition for 3,3-DM-2-B. In the L phase, the D values were on the order of 10 −12 to 10 −10 m 2 /s for 2,2-DM-1-B and 3,3-DM-1-B, whereas for 3,3-DM-2-B, D values on the order of 10 −10 m 2 /s were found, although with a large error because of the small slope of the R 1 (ω) vs ω curves.…”

“…) certainly contributes to relaxation in the liquid phase, as already pointed out in a previous study, 66 but it might also affect relaxation in the ODIC phases, as reported in the literature for other plastic crystals. [6][7][8]12,52,53 The R 1 IM and R 1 MR contributions were expressed as 54,55…”

“…Thanks to the possibility of combining T 2 , T 1 , and especially T 1ρ relaxation times measured at different frequencies and temperatures, and for different nuclei (most commonly 1 H, but also 13 C and 2 H), NMR relaxometry allowed internal, reorientational, and self-diffusion molecular motions to be investigated for several molecules showing plastic crystalline phases. − In this context, fast field cycling (FFC) 1 H NMR relaxometry, a technique allowing 1 H T 1 values to be measured over a wide frequency range with a single instrument (0.01–40 MHz with commercial relaxometers, the lower limit being extended even below 100 Hz in homemade relaxometers − ), was found to be particularly suited for investigating both reorientational and translational dynamics in these phases. In fact, 1 H longitudinal relaxation results from the fluctuations of both intra- and intermolecular dipole–dipole interactions between pairs of nuclei caused by molecular reorientations and translational motions.…”