The mean squared torque in pure and mixed dense fluids |
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Authors: | C.H. Twu C.G. Gray K.E. Gubbins |
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Affiliation: | 1. Department of Chemical Engineering , University of Florida , Gainesville, Florida, 32611, U.S.A.;2. Department of Physics , University of Guelph , Guelph, Ontario, Canada;3. Department of Physics , University of Guelph , Guelph, Ontario, Canada;4. Chemical Engineering Department , University of Florida , Gainesville, Florida, 32611, U.S.A. |
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Abstract: | The mean squared torque on a molecule can be obtained from infra-red or Raman band moments, and provides a direct measure of the strength of the anisotropic intermolecular forces. The expression for the mean squared torque on a molecule of species α in a fluid mixture is given in terms of the intermolecular potential and the angular pair correlation functions. This relation is made tractable by introducing a perturbation expansion in powers of the anisotropic potential strength for the angular pair correlation functions. Monte Carlo calculations of the mean squared torque are presented for a liquid of linear molecules having dipolar, quadrupolar and anisotropic overlap interactions. Comparison of the perturbation expansion to second order with these ‘exact’ results shows good agreement for μ*=μ/(εσ3)1/2 and Q*=Q/(εσ5)1/2 values less than about 0·5, and for values of the dimensionless overlap constant |δ| less than about 0·2. Finally, experimental values of the mean squared torque for both pure and mixed liquids are compared to the Monte Carlo and to the perturbation theory results. |
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