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.