The fundamental influence of thermal gradients on the flux has received scanty attention until only the past decades. Thermophoretic phenomena were firstly studied for numerous applications such as optothermal DNA trap [1] or disease-related protein aggregates [2]. On the other hand, thermo-osmosis at solid-liquid interfaces is the least studied among the osmotic phenomena. It is usually interpreted as a thermal gradient-induced Marangoni flow, but the molecular level understanding is still lacking. Using molecular dynamics simulations, we measured the thermo-osmosis coefficient by both mechanocaloric and thermo-osmosis routes, against different solid-liquid interfacial energies. We show that a modified Derjaguin's formula [3, 4] which takes into account the interfacial hydrodynamic conditions describes well the simulation results. For a non-wetting surface, thermo-osmosis transport is controlled and largely amplified by the existence of a slippage at the interface. Whereas for a wetting surface, the position of the hydrodynamic shear plane plays a key role in the determination of thermo-osmosis coefficient. The thermo-osmosis coefficient decreases for increasing wettability and a change of sign is clearly observed. A hydrodynamic backflow induced by hydrodynamic entrance effects is found in the thermo-osmosis route measurements, and is found to decrease significantly the amplitude of the thermo-osmotic effect.
1. Duhr, S. & Braun, D. Thermophoretic depletion follows Boltzmann distribution. Phys. Rev. Lett. (2006).
2. Wolff, M. et al. Quantitative thermophoretic study of disease-related protein aggregates. Scientific Reports 6, 22829 (2016).
3. Derjaguin, B. V., Churaev, N. V. & Muller, V. M. in Surface Forces 231–291 (Springer US, 1987). doi:10.1007/978-1-4757-6639-4_7
4. Fu, L. Merabia, S & Joly, L. in preparation
