Study of Sign Change of the Soret Coefficient of Poly(Ethylene Oxide) in Water/Ethanol Mixtures Observed by Thermal Diffusion Forced Rayleigh Scattering (CAT#: STEM-ST-0068-YJL)

Introduction

The presence of a temperature gradient in a fluid mixture generally induces mass flows, which create concentration gradients in the mixture. This process is known as the Ludwig-Soret effect. In a binary mixture, the size of the effect is characterized by the Soret coefficient, which relates the gradient of the concentration to the gradient of the temperature in the steady state.
The Soret coefficient is properly called the Soret coefficient of component 1. It has a positive sign when component 1 migrates to the cold side and a negative sign when component 1 migrates to the warm side. In a binary mixture, the Soret coefficient can be expressed as ST =(DT /D), where DT is the thermal diffusion coefficient and D is the ordinary translational diffusion coefficient Thermal diffusion in gas mixtures is well described by the Chapman-Enskog theory.