Statistical thermodynamic expression for the Soret coefficient

Institute of Biochemical Physics, RAS - Kosygin Street 4, 119334 Moscow, Russia

Corresponding author: sem@triniti.ru

Received: 21 March 2010
Accepted: 28 May 2010

Abstract

The thermodynamic Soret coefficient for diluted mixtures expressed through the temperature derivative of the particle chemical potential at constant pressure is calculated using statistical mechanics. The local pressure distribution is obtained using the condition of the local thermodynamic equilibrium around an isolated particle. The Laplace contribution to the local pressure distribution within the layer of the liquid around the particle is accounted. The calculations yield results equivalent to the hydrodynamic approach and add a new kinetic term to the Soret coefficient. This term is related to the difference in the thermal velocities between the particles with different mass. The kinetic contribution to thermodiffusion explains the isotope thermodiffusion effect observed in molecular systems. The theory describes most of the experimental data on thermodiffusion of the isolated molecular and colloid particles placed in non-electrolyte liquids.