Collective thermodiffusion of colloidal suspensions

The thermophoretic behavior of concentrated colloidal suspensions can be understood as the sum of single particle and collective effects. Here, we present a simulation model to investigate the particularities of the collective thermodiffusive effects in concentrated uncharged solutions, where the influence of different colloid-colloid interactions is analyzed. The concentration dependence found in our simulations qualitatively agrees with experimental results. Colloids with repulsive interactions are found to accumulate more effectively than the solvent in the warm areas, such that the corresponding Soret coefficients are negative and decrease with increasing concentration. The accumulation of colloids in the cold regions is facilitated by attraction, such that colloids with attractive interactions have larger values of the Soret coefficient. A thermodynamic argument that explains our results from equilibrium quantities is discussed as well.