Ludwig–Soret effect in a linear temperature field: Theory and experiments for steady state distributions

The Ludwig–Soret effect, also known as thermal diffusion, describes the separation of mixtures in the presence of a temperature gradient. Here, a solution to the nonlinear differential equation that describes the motion of components of a binary mixture in a linear temperature field is given for long times, when the distribution of the components in space becomes time independent. A new experimental method based on the use of a scanning confocal microscope to monitor the spatial distribution of fluorescence from fluorescein labelled nanoparticles in water in a linear temperature field is described.

► We give a steady state solution to the Ludwig–Soret equation. ► We give a method of finding Soret parameters based on terminal spatial distributions. ► We introduce a new experimental method based on probing with a confocal microscope. ► The method is applied to studying fluorescent nanoparticles suspended in water.