25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Second-Order Effects in 11B NMR Exploited to Study Fast and Slow Dynamics of the Inorganic Molecular Glass Former Trimethoxyboroxine

Not scheduled
4h
Harnack House and Henry Ford Building

Harnack House and Henry Ford Building

Board: 183
Poster Posters

Speaker

Lars Hoffmann

Description

NMR is a powerful tool to unravel the molecular dynamics in viscous liquids, polymers, and melts. Most of the applications in this field focus on organic materials and typically they employ spin-1/2 nuclei. Conversely, for many inorganic glass formers one has to use compounds for which quadrupolar interactions prevail. Here we explore the static and dynamic properties of liquid and glassy trimethoxyboroxine (TMB). In contrast to most inorganic boron-containing covalently bonded networks, TMB represents a molecular glass former, held together by van der Waals attractions. Consequently, TMB shows a low glass transition temperature which, using broadband dielectric spectroscopy, is determined to take place near 205 K. Low-temperature 11B MAS experiments are carried out in order to obtain the quadrupolar anisotropy and asymmetry parameters. At higher temperatures, however, the MAS line shapes are analyzed for the determination of motional time scales and geometries. The same goal is pursued by carrying out stimulated-echo measurements and two-dimensional exchange spectroscopy on nonrotating samples. To extend the range in which the molecular dynamics of TMB can be studied up to much higher temperatures, we exploit dynamic second-order shifts, non-monotonic linewidth effects, and spin relaxation times. Several of the experimental results are compared with random-walk simulations to further deepen our understanding of the dynamics for TMB, a member of this barely studied class of inorganic glass formers.

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