Thermodiffusion in colloidal suspensions

A temperature gradient applied to a colloidal suspension induces a mass flux, an effect which
is know as thermodiffusion. This phenomenon is studied by means of a mesoscopic simulation
method denoted as Multi Particle Collision dynamics. This method incorporates hydrodynamic
interactions, thermal fluctuations and heat transport, i. e. the capability to implement temperature gradients.

The diffusive drift motion of colloidal particles in a system with inhomogeneous temperature
can be directed towards the cold or the warm side of the suspension. On the single particle level,
the driving force behind this effect arises from interactions between the colloid surface and the
solvent. We analyze the role of colloid-solvent interactions by simulating single colloids with
different interaction potentials. It is observed that repulsive interactions lead to a drift to the
warm side, whereas attractive interactions facilitate a tendency for the colloid being pulled to
the cold. We show how the so called thermophoretic force depends on the particle size with
respect to different colloid-solvent interaction potentials.

In a different study, concentrated suspension are investigated with respect to varying volume
fractions and different colloid-colloid interaction potentials. We compare our results to experiments, in which a macromolecular coating of the colloid surface leads to temperature dependent
colloid-colloid interactions.