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Comparative Studies of the Dynamics in Viscous Liquids by Means of Dielectric Spectroscopy and Field Cycling NMR
Ist Teil von
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 2010-08, Vol.114 (30), p.7847-7855
Ort / Verlag
United States: American Chemical Society
Erscheinungsjahr
2010
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
1H nuclear magnetic resonance (NMR) field cycling relaxometry has been applied to study the dynamics of homologues of glycerol (propylene glycol, 2,3-butandiol, glycerol, threitol, xylitol, sorbitol) and non-alcohol liquids (o-terphenyl, tristyrene, 3-fluoroaniline, m-toluidine). A broad range of temperatures (200−400 K) is covered, including the supercooled state. From the dispersion of the spin−lattice relaxation rate, R 1(ω) = T 1 −1(ω), the susceptibility representation, ωT 1 −1(ω), has been derived and compared with the susceptibility data from dielectric spectroscopy (DS). The DS spectra can be interpolated by a Cole−Davidson (CD) function, yielding correlation times which are attributed to the structural relaxation (α-process) in the supercooled state. In contrast to that, most of the 1H NMR susceptibility spectra show, in addition to the α-relaxation peak, a low-frequency excess contribution with amplitudes varying among the systems. Exceptions are o-terphenyl and tristyrene for which DS and NMR susceptibility curves agree well and both can be reproduced by a CD function. Possible explanations of the low-frequency contribution are discussed. In particular the role of translational diffusion probed via the intermolecular coupling of 1H spins is considered since it may likely generate the low-frequency excess intensity.