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Diffusivity and Nuclear Spin Relaxation Measurements at High Pressure in Methanol

Published online by Cambridge University Press:  10 February 2011

R. F. Marzke
Affiliation:
Department of Physics and Arizona State University, Tempe, AZ 85287
D. P. Raffaelle
Affiliation:
Department of Physics and Arizona State University, Tempe, AZ 85287
G. H. Wolf
Affiliation:
Department of Chemistry, Arizona State University, Tempe, AZ 85287
J. L. Yarger
Affiliation:
Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720
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Abstract

Diffusivity D and nuclear spin relaxation times T1 and T2 have been measured by NMR to 4.0 GPa in methanol, using a diamond anvil cell probe. In pure MeOH, D−1 and T2 show essentially identical activation volumes. However, these are ∼18% larger than the activation volume of viscosity. By relating these observations to an average molecular correlation time a pressure-dependent infinite-frequency shear modulus G∞ can be inferred, using two independent approaches. The relation between diffusivity and viscosity shows increasing departure from Stokes-Einstein behavior with increasing pressure, if a constant hydrodynamic radius is assumed. This departure is attributed to the pressure dependence of G∞, and can be described empirically by a simple modification of the Stokes-Einstein relation.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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References

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