Thermoosmosis

Thermoosmosis is the transport of solvent through a semipermeable membrane driven by a temperature gradient across the membrane. It is distinct from classical osmosis, which is driven by differences in solute concentration; thermoosmosis arises from the temperature dependence of the solvent’s chemical potential and from interactions between solvent molecules and the pore surfaces.

When a membrane separates regions at different temperatures, the solvent experiences forces associated with the temperature gradient. Interfacial interactions within the pores, adsorption properties, and temperature-dependent viscosity can produce a net solvent flux. The magnitude and direction of flow depend on the system, including the solvent, membrane material, and pore size, and can be described by a thermo-osmotic coefficient that relates the temperature gradient to the induced flux. In simple terms, the cross-membrane temperature difference drives solvent movement in a characteristic direction.

Applications and relevance: thermoosmosis is studied in nanofluidics and membrane science, where heat gradients across nanopores or membranes can drive solvent transport without external pressure. It has implications for desalination and other filtration processes under nonuniform heating, and it can be used to implement thermally driven pumping in microfluidic systems. Thermoosmosis is distinct from thermophoresis, which concerns the motion of solute particles in a temperature gradient rather than solvent transport through a membrane.