The Seebeck effect results from charge carrier diffusion along the thermal gradient. For water, however, Bresme, Lervik, Bedeaux, and Kjelstrip find that thermal reorientation of water molecules can lead to polarization of the bulk liquid, resulting in a sizeable electrostatic field. To examine this effect, the researchers carried out nonequilibrium molecular dynamics simulations with up to 3240 water molecules confined to a rectangular box having heat sources on the edges. As a reality check, the authors obtained good agreement between their simulated equation of state (which relates values such as temperature, pressure, volume and internal energy) and experimental data.
To obtain the electrostatic field gradient, Bresme et al. calculated the spatial charge distribution. For thermal gradients in the neighborhood of K/m they observe fields of about V/m, but where do such extreme conditions exist? In fact, the authors note, these field gradients are characteristic of biomembranes and ionic thin films as well as of the conditions found in nanoparticle systems that experience heating from absorption of electromagnetic radiation. A better understanding of such effects may be relevant in proposals to destroy cancer cells with nanoparticles and radiation sources. - David Voss