Friday, 21 July, 2006
Thermophoretic Depletion Follows Boltzmann Distribution
Stefan Duhr and Dieter Braun -
Phys. Rev. Lett. 96, 168301 (2006)
Thermophoresis, also termed thermal diffusion or the Soret effect, moves particles along temperature gradients. For particles in liquids, the effect lacks a theoretical explanation. We present experimental results at moderate thermal gradients: (i) Thermophoretic depletion of 200 nm polystyrene spheres in
water follows an exponential distribution over 2 orders of magnitude in concentration; (ii) Soret coefficients scale linearly with the sphere’s surface area. Based on the experiments, it is argued that local thermodynamic equilibrium is a good starting point to describe thermophoresis.