Thermocharge of a hot spot in an electrolyte solution

We discuss the thermoelectric properties of a locally heated micron-size volume in an electrolyte solution. We find that such a hot spot carries a net charge Q which, for an excess temperature of 10 K, may attain hundreds of elementary charges. The corresponding Seebeck electric field E increases linearly with the radius r inside the heated area, then goes through a maximum, and decays as 1/r2 at larger distances. Our results could be relevant to optothermal actuation of electrolytes and colloidal suspensions.