Thermal diffusion in liquid mixtures and polymer solutions

Thermodiffusion, also called thermal diffusion or the Ludwig-Soret effect, describes the coupling between a temperature gradient and a resulting mass flux in a multicomponent system. Although Ludwig and Soret discovered the effect in the 19th century, there is so far no molecular understanding of thermodiffusion in liquids. In the past decade the Ludwig-Soret effect has attracted growing interest due to improved experimental techniques, especially modern optical methods, which will be discussed and compared. On the basis of theoretical models, simulations and recent experiments we elucidate some properties and mechanisms contributing to the Soret effect.