Generating Shear Flows without Moving Parts by Thermo-osmosis in Heterogeneous Nanochannels.

Shear flows play critical roles in biological systems and technological applications and are achieved experimentally using moving parts. However, when the system size is reduced to micro- and nanoscale, fabrication of moving parts becomes exceedingly challenging. We demonstrate that a heterogeneous nanochannel composed of two parallel walls with different wetting behaviors can generate shear flow without moving parts. Molecular dynamics simulations show that shear flows can be formed inside such a nanochannel under a temperature gradient. The physical origin is that thermo-osmosis velocities with different rates and directions can be tuned by wetting behaviors. Our analysis reveals that thermo-osmosis is governed by surface excess enthalpy and nanoscale interfacial hydrodynamics. This finding provides an efficient method of generating controllable shear flows at micro- and nanoscale confinement. It also demonstrates the feasibility of using fluids to drive micromechanical elements via shear torques generated by harvesting energy from temperature differences.