Thermo-osmotic flow in slit channels with boundary slip: giant flow amplification between polarized graphene surfaces

Abstract

The thermo-osmotic flow (TOF) of an electrolyte solution in a slit channel with a Navier slip condition at the channel walls is studied. An analytical expression for the TOF velocity profile, based on the long-wavelength and Debye–Hückel approximations, is derived and compared to numerical solutions based on the finite-element method. The TOF between graphene surfaces whose charge is created via polarization through an applied electric field is considered as a special case. Using the relationship between the surface charge and the slip length obtained from molecular dynamics simulations, a giant flow amplification is uncovered. Specifically, for such flow in a channel with a width of 10 nm, compared to the flow between no-slip walls, a flow velocity enhancement by a factor of up to 250 is predicted.

Complex coupling between surface charge and thermo-osmotic phenomena

“…There is an increasing effort to better understand thermo-osmotic flows, through experimental characterization 23,24 and modeling. 25–37 As detailed in the Theory section, for liquids, Derjaguin and collaborators developed a standard theoretical framework, 13,38–40 which relates the thermo-osmotic flow velocity to the interfacial enthalpy excess, stemming from the interactions of the liquid with the solid. This framework has been extended recently to take into account liquid–solid slippage arising on low-friction surfaces, 13,26,41 which can boost the flow.…”