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.<br />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.