Geometry and time scale of the rotational dynamics in supercooled toluene

Abstract

Multidimensional deuteron NMR provides powerful tools for studying molecular reorientation in supercooled liquids. We present results on selectively deuterated toluene-d 5 , which may be one of the molecularly most simple van der Waals glass formers. From two-time correlation functions the time scale of reorientation was obtained slightly above the calorimetric glass transition temperature. The applied stimulated echo method provides a geometry parameter that, in analogy to q-dependent scattering experiments, allows one to investigate the geometry of the elementary rotational process. Continuous time random walk computer simulations were used for the interpretation of the data. It is shown that an isotropic single jump angle model does not describe the toluene rotation, rather the existence of several jump angles is required. Assuming mainly small jump angles Ͻ6°but also some larger angles up to 30°an acceptable fit to the experimental data was obtained. Using four-time correlation functions further properties of molecular reorientation are elucidated. Slow reorienting subensembles can be selected. Their return to the full ensemble occurs on the same time scale as the elementary rotational jump process. In accord with previous investigations in other supercooled liquids, a heterogeneous scenario is found for the rotational dynamics of toluene.

Local viscosity of supercooled glycerol near T g probed by rotational diffusion of ensembles and single dye molecules

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Two-Dimensional 109Ag NMR and Random-Walk Simulation Studies of Silver Dynamics in Glassy Silver Ion Conductors

“…Despite the above-mentioned restrictions it was shown recently that 6 Li ðI ¼ 1Þ and 7 Li ðI ¼ 3=2Þ can be used to study Li þ motion in crystalline ion conductors by means of static 2D NMR [22][23][24]. For both types of nuclei, the strength of the quadrupolar interaction is moderate and, at least in 2D NMR, it is possible to apply simple pulse sequences.…”

“…Two-dimensional (2D) NMR experiments in the frequency and in the time domain yield valuable information about the time constants and the geometry of a motional process. They have proven the utility to investigate the primary relaxation in various supercooled liquids such as polymers [2,4], organic low-molecular weight compounds [5][6][7] and inorganic glass formers [8] and frozen solutions [9]. Further, small-angle fluctuations of a few degrees attributed to the secondary relaxation of organic glass formers below the glass transition have been studied in detail [10][11][12].…”

Nuclear magnetic resonance and dielectric spectroscopy of a simple supercooled liquid: 2-methyl tetrahydrofuran

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