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(in∞} 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.
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Acknowledgements
We thank M. Scheinfein for calculations of the DC magnetic field in the diamond anvil cell, and R. Nieman for discussions and assistance throughout this project. J. L. Yarger would also like to thank the NSF-PFSMETE program. This work was supported by National Science Foundation under grants CHE-9012249, CHE-9214799, DGE-9714523 and DMR-9632635.
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Marzke, R.F., Raffaelle, D.P., Wolf, G.H. et al. Diffusivity and Nuclear Spin Relaxation Measurements at High Pressure in Methanol. MRS Online Proceedings Library 499, 295–300 (1997). https://doi.org/10.1557/PROC-499-295
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DOI: https://doi.org/10.1557/PROC-499-295