Tunable direction reverses of thermo-osmotic flow in a nanochannel by introducing surfactant

Thermo-osmosis is a fluid flow phenomenon in a nanochannel caused by thermal gradients . Generally, reversing the direction of thermo-osmosis requires structural modifications, which limit practical applications. This paper proposes a surfactant-based method to reverse the direction of thermo-osmosis without altering the nanochannel. Molecular dynamics simulations demonstrate that the direction and strength of thermo-osmotic flow in nanochannels can be tuned by varying the surfactant concentration. The introduction of surfactants into the fluid significantly alters the distribution of interfacial free energy . By calculating the potential of mean force, it is found that the addition of the surfactant can reverse the flow direction from positive (high-to-low temperature) to negative (low-to-high temperature), which is attributed to the sign change in the slope of the potential of mean force distribution along the flow direction. Numerical studies further quantify the influence of channel width, surfactant hydrophilicity , and system temperature on the critical reversal concentration. This work presents a tunable, structure-independent method for reversing the direction of thermo-osmosis, thereby advancing applications in adaptive nanofluidics and energy-efficient thermal management. • A new method is proposed to reverse the flow direction of thermo-osmosis in a nanochannel. • The direction reversal involves only the addition of a surfactant with a volume fraction of 0.1 without structural modifications. • The reversal is attributed to the sign change in the slope of the potential of mean force distribution.