Relationship between Viscosity Coefficients and Volumetric Properties Using a Scaling Concept for Molecular and Ionic Liquids
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- 作者：Alfonso S. Pensado ; Agí ; lio A. H. Pá ; dua ; Marí ; a J. P. Comuñ ; as ; Josefa Ferná ; ndez
- 刊名：Journal of Physical Chemistry B
- 出版年：2008
- 出版时间：May 8, 2008
- 年：2008
- 卷：112
- 期：18
- 页码：5563 - 5574
- 全文大小：372K
- 年卷期：v.112,no.18(May 8, 2008)
- ISSN：1520-5207
文摘
In this work, a scaling concept based on relaxation theories of the liquid state was combined with a relationpreviously proposed by the authors to provide a general framework describing the dependency of viscosityon pressure and temperature. Namely, the viscosity-pressure coefficient (
/p)T was expressed in terms ofa state-independent scaling exponent, 
. This scaling factor was determined empirically from viscosity versusTv curves. New equations for the pressure- and temperature-viscosity coefficients were derived, which areof considerable technological interest when searching for appropriate lubricants for elastohydrodynamiclubrication. These relations can be applied over a broad range of thermodynamic conditions. The fluidsconsidered in the present study are linear alkanes, pentaerythritol ester lubricants, polar liquids, associatedfluids, and several ionic liquids, compounds selected to represent molecules of different sizes and with diverseintermolecular interactions. The values of the exponent determined for the fluids analyzed in this workrange from 1.45 for ethanol to 13 for n-hexane. In general, the pressure-viscosity derivative is well-reproducedwith the values obtained for the scaling coefficient. Furthermore, the effects of volume and temperature onviscosity can be quantified from the ratio of the isochoric activation energy to the isobaric activation energy,Ev/Ep. The values of and of the ratio Ev/Ep allow a classification of the compounds according to the effectsof density and temperature on the behavior of the viscosity.
/p)T was expressed in terms ofa state-independent scaling exponent, . This scaling factor was determined empirically from viscosity versusTv curves. New equations for the pressure- and temperature-viscosity coefficients were derived, which areof considerable technological interest when searching for appropriate lubricants for elastohydrodynamiclubrication. These relations can be applied over a broad range of thermodynamic conditions. The fluidsconsidered in the present study are linear alkanes, pentaerythritol ester lubricants, polar liquids, associatedfluids, and several ionic liquids, compounds selected to represent molecules of different sizes and with diverseintermolecular interactions. The values of the exponent determined for the fluids analyzed in this workrange from 1.45 for ethanol to 13 for n-hexane. In general, the pressure-viscosity derivative is well-reproducedwith the values obtained for the scaling coefficient. Furthermore, the effects of volume and temperature onviscosity can be quantified from the ratio of the isochoric activation energy to the isobaric activation energy,Ev/Ep. The values of and of the ratio Ev/Ep allow a classification of the compounds according to the effectsof density and temperature on the behavior of the viscosity.