Direction reverse of the thermo-osmosis for a liquid in a nanochannel

Thermo-osmosis describes the fluid flow due to thermal gradients. Usually, thermo-osmosis for a liquid is from high to low temperature. However, in certain cases, the direction of the thermo-osmosis can be reversed (from low to high temperature), i.e., negative thermo-osmosis, and the underlying mechanism for the direction reverse of the thermo-osmosis is still unclear. In the present paper, we study the direction reverse of thermo-osmosis for a liquid in nanochannels by using molecular dynamics simulations. The research findings indicate that the direction and strength of thermo-osmosis depend significantly on the interaction strength between the solid and liquid. The analysis of the potential mean force distribution along the flow direction reveals that the change from positive to negative thermo-osmosis is linked to a reversal in the slope of the potential mean force distribution. Therefore, the sign of the slope of potential mean force distribution can be used as a criterion to predict the direction of thermo-osmosis. The findings in the present paper pave the way for the application of the thermo-osmosis phenomenon.