I. Zupančič

NMR self-diffusion study of organic glasses: COANP, MBANP, PNP, NPP

A pulsed field gradient proton spin-echo NMR self-diffusion study of organic glasses COANP, MBANP, PNP and NPP in their liquid and weakly supercooled states was performed. The NMR phase diagrams, based on the proton NMR transverse relaxation time (T2) temperature hysteresis data of these materials, clearly give evidence of the onset of a glass phase on cooling the isotropic liquids below their respective melting temperatures. The self-diffusion data exhibit in the supercooled glassy state a non-Arrhenius behaviour and can be described in terms of the Vogel-Fulcher modification of the Arrhenius law,D=D∞exp{−Ea/[kB(T−TVF)]}. The activation energiesEa and Vogel-Fulcher temperaturesTVF are 83.2 meV and 239 K for COANP, 66 meV and 249 K for MBANP, and 85 meV and 245 K for PNP, respectively. The flow viscosity data obtained for COANP in the same temperature region as well conform to the Vogel-Fulcher behaviour, η∝exp{Ea(η)/[kB(T−TVF)]}, withEa(η)=80.4 meV andTVF=239 K. In case of COANPD was found to increase with decreasing diffusion time in the supercooled (glassy) melt just belowTM whereas no such behaviour was found aboveTM.

Effect of the background gradients on PGSE NMR diffusion measurements

Abstract In spatial inhomogeneous samples large local gradients can be created. It is shown that the background gradient tends to compensate the pulsed gradient and the echo attenuation is dimished with increasing diffusion time.

Proton dipolar spin-lattice relaxation in hexagonal ice

The ultraslow motion of defects in high purity hexagonal H2O ice has been studied by proton dipolarT1D measurements in the “strong collision” limit, using the Jeener technique. The obtained NMR correlation times τ agree rather well with both the Schottky H2O diffusion timests=〈r2〉/6D and the deuteron correlation times in D2O ice, suggesting that Schottky rather than interstitial diffusion dominates spin-lattice relaxation in both H2O and D2O ice.

Dimer Formation and its Reflection on the Self-Diffusion Coefficient

Abstract The self-diffusion coefficients of nematic liquid crystals p-n-heptyloxybenzoic acid and p-n-nonyloxybenzoic acid have been measured depending on the temperature. The influence of the process of dimer formation on the self-diffusion was shown.