Internal Degrees of Freedom as a Basis for Isotopic Effects in Thermodiffusion.

We present a model that relates isotope effects in thermodiffusion to changes in internal degrees of freedom associated with rotational and vibrational motion. The model uses general material transport equations for binary non-isothermal liquid systems, derived using non-equilibrium thermodynamics in our previous work. The equilibrium chemical potentials of the components at constant pressure are derived using statistical mechanics. In evaluating the model, we use experimental data on changes in the Soret coefficient of various hydrocarbons in perprotonated and perdeuterated cyclohexane. We also compare predictions of the model with experimental data on the Soret coefficient in isotopic mixtures. In all cases, the model is consistent with experimental data and computations.

[1]  J. Rubí,et al.  Role of Interfacial Entropy in the Particle-Size Dependence of Thermophoretic Mobility. , 2020, Physical review letters.

[2]  S. Semenov,et al.  Comparative Examination of Nonequilibrium Thermodynamic Models of Thermodiffusion in Liquids , 2019, Proceedings.

[3]  S. Semenov,et al.  Statistical thermodynamics of material transport in nonisothermal suspensions. , 2015, The journal of physical chemistry. B.

[4]  S. Semenov,et al.  Theory of Soret coefficients in binary organic solvents. , 2014, The journal of physical chemistry. B.

[5]  S. Semenov.  Statistical thermodynamics of material transport in non-isothermal binary systems , 2012 .

[6]  W. Köhler,et al.  The isotope Soret effect in molecular liquids: a quantum effect at room temperatures , 2012 .

[7]  S. Semenov,et al.  Internal Degrees of Freedom, Molecular Symmetry and Thermodiffusion , 2011 .

[8]  S. Semenov,et al.  Mass transport thermodynamics in nonisothermal molecular liquid mixtures , 2009 .

[9]  N. R. Rao,et al.  On the relative intensities of the Raman active fundamentals, r0 structural parameters, and pathway of chair–boat interconversion of cyclohexane and cyclohexane‐d12 , 2009 .

[10]  Roberto Piazza,et al.  Thermophoresis in colloidal suspensions , 2008 .

[11]  Roberto Piazza,et al.  Thermophoresis of microemulsion droplets: size dependence of the Soret effect. , 2007, Physical review. E, Statistical, nonlinear, and soft matter physics.

[12]  D. Braun,et al.  Thermodiffusion of charged colloids: single-particle diffusion. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[13]  F. Montel,et al.  Mass Effect on Thermodiffusion using Molecular Dynamics , 2007 .

[14]  W. Köhler,et al.  Universal isotope effect in thermal diffusion of mixtures containing cyclohexane and cyclohexane-d12. , 2005, The Journal of chemical physics.

[15]  K. Wirtz.  Isotopentrennung durch Thermodiffusion in Flüssigkeiten nach der kinetischen Theorie , 1943, Naturwissenschaften.

[16]  J. Caltagirone,et al.  Thermal diffusion sensitivity to the molecular parameters of a binary equimolar mixture, a non-equilibrium molecular dynamics approach , 2003 .

[17]  John L. Anderson,et al.  Colloid Transport by Interfacial Forces , 1989 .

[18]  W. Rutherford.  Effect of mass distribution on the isotopic thermal diffusion of substituted benzenes , 1984 .

[19]  J. Kirkwood,et al.  Statistical Mechanics of Transport Processes. XI. Equations of Transport in Multicomponent Systems , 1958 .

[20]  I. Prigogine,et al.  Recherches Sur La Thermodiffusion En Phase Liquide: Thermodiffusion De L'eau Lourde , 1952 .