Hydrodynamic boundary effects on thermophoresis of confined colloids

Aloïs Würger (1)

1 LOMA - Laboratoire Ondes et Matière d'Aquitaine

We study hydrodynamic slowing-down of a particle moving in a temperature gradient perpendicular to a wall. At distances much smaller than the particle radius, h << a, lubrication approximation leads to the reduced velocity u/u0 = 3 h/a (ln(a/h) − 9/4), where u0 is the velocity in the bulk. With Brenner's result for confined diffusion, we find that the trapping efficiency, or effective Soret coefficient , increases logarithmically as the particle gets very close to the wall. Our results provide a quantitative explanation for the recently observed enhancement of thermophoretic trapping at short distances. Our discussion of parallel and perpendicular thermophoresis in a capillary, reveals a good agreement with experiments on charged polystyrene particles, and sheds some light on a controversy concerning the size-dependence and the non-equilibrium nature of the Soret effect.

Domaines: Matière Molle [cond-mat.soft]

Aloïs Würger. Hydrodynamic boundary effects on thermophoresis of confined colloids. Physical Review Letters, 2016, 116, pp.138302. ⟨10.1103/PhysRevLett.116.138302⟩. ⟨hal-01289232⟩