We study the temperature field and the resulting flow pattern in the vicinity of a heated metalcapped Janus particle. If its thickness exceeds about ten nanometers, the cap forms an isotherm and the flow pattern comprises a quadrupolar term that decays with the square of the inverse distance ∼ r −2 . For much thinner caps the velocity varies as ∼ r −3 . These findings could be relevant for collective effects in dense suspensions and for the circular tracer motion observed recently in the vicinity of a tethered Janus particle.

We study the Soret effect of charged polystyrene particles as a function of temperature and electrolyte composition. As a main result we find that the Soret coefficient is determined by charge effects, and that non-ionic contributions are small. In view of the well-known electric-double layer interactions, our thermal field-flow fractionation data lead us to the conclusion that the Soret effect originates to a large extent from diffusiophoresis in the salt gradient and from the electrolyte Seebeck effect, both of which show strong specific-ion effects. Moreover, we find that thermophoresis of polystyrene beads is fundamentally different from proteins and aqueous polymer solutions, which show a strong non-ionic contribution.