Clarifying the Role of Thermoelectriciy and Specific Ions/Molecules Effects in the Thermodiffusion of Charged Iron Oxide Nanoparticles*

A temperature gradient applied to a liquid solution of ferrofluid will induce the thermodiffusion effect of electrostatically stabilized iron oxide nanoparticles. The driving mechanisms of thermophoretic migration of the particles either to the cold or to the hot side come from microscopic phenomena. They are particle localized, like the temperature dependence of electric double layer and the Brownian diffusion along the temperature gradient; or long range like the thermoelectric field due to the differential ionic heats of transport of stabilizing ions or the concentration gradient generated by the intrinsic Soret coefficient of these ions. We will present experimental results for the Soret coefficient of nanoparticles and investigate the contributions of the different mechanisms by the use of auxilliary experiments like the measument of the zeta potential, the analysis of the thermoelectric field generated by thermodiffusion and the measurement of the intrinsic Soret effect of the stabilizing ions.