The direction reversal of thermo-osmotic flow in a nanochannel

K Qi and ZR Li and SB Zhuo and J Wang and GD Xia and ZG Li, PHYSICS OF FLUIDS, 37, 072025 (2025).

DOI: 10.1063/5.0267187

Thermo-osmosis describes the flow of a liquid or dense fluid along a surface caused by a temperature gradient. However, predicting the direction of thermo-osmotic flows at the nanoscale is challenging because the direction is usually affected by the solid-liquid coupling strength. Based on molecular dynamics simulations, this work investigates the mechanism of the direction reversal of thermo-osmosis for a liquid in a nanochannel by adjusting the coupling strength parameter (k). The thermo-osmotic coefficient and the thermo-osmotic force are calculated using microscopic and excess enthalpy methods. The results indicate a correlation between the direction reversal of thermo- osmosis and the thermo-osmotic force, which is dominated by the surface forces. For weak couplings (k <= 0.6), the driving force for fluid flow is from high to low temperatures (i.e., positive thermo-osmosis). For strong couplings (k > 0.6), the thermo-osmotic force is in the opposite direction (from low to high temperatures, i.e., negative thermo- osmosis). The direction reversal of thermo-osmosis occurs due to the reversal of the thermo-osmotic force. The results of the present paper can provide a deep understanding of the control of flows in nanochannels.

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