(720d) Slip and Spin-Coupling: Foundations of the Flow Enhancement of Fluids in Graphene Slit Channels and Carbon Nanotubes With Important Applications in Nanoscale Fluid Pumping

We present both theoretical and simulation studies that clearly demonstrate the importance of several non-classical phenomena that are fundamental features of fluid flow under extreme confinement. These are: (1) the prevalence of slip and (2) the strong coupling of molecular spin to linear translational momentum for molecularly structured fluids. In the first of these, we utilize a newly developed equilibrium based model¹ to accurately predict the slip velocity and slip lengths of systems such as water or methane flowing in graphene nanochannels and carbon nanotubes^2-4. We demonstrate that traditional nonequilibrium molecular dynamics simulations of such systems are far less efficient and accurate than the easily implemented model we propose. Our results confirm large flow enhancements that are accurately quantified and compared to existing experimental, theoretical and simulation data in the literature. Next, we show that ignoring the coupling of spin angular momentum to linear translational motion of a highly confined fluid can lead to significant over-estimation of the predicted flow rates using conventional Navier-Stokes treatments. By including spin-coupling into the extended Navier-Stokes equations, hydrodynamic prediction is seen to be very accurate down to length scales of a few atomic diameters⁵. We also demonstrate how this knowledge, coupled with our knowledge of slip, can be used to pump molecular fluids such as water via non-intrusive application of a rotating electric field^6-8.

¹J.S. Hansen, B.D. Todd and P.J. Daivis. Phys. Rev. E 84, 016313 (2011).

²S. K. Kannam, B.D. Todd, J.S. Hansen and P.J. Daivis. J. Chem. Phys. 135, 144701 (2011).

³S. K. Kannam, B.D. Todd, J.S. Hansen and P.J. Daivis. J. Chem. Phys. 136, 024705 (2012).

⁴S. K. Kannam, B.D. Todd, J.S. Hansen and P.J. Daivis. J. Chem. Phys. 138, 094701 (2013).

⁵J.S. Hansen, J.C. Dyre, P.J. Daivis, B.D. Todd and H. Bruus. Phys. Rev. E 84, 036311 (2011).

⁶J. D. Bonthuis, D. Horinek, L. Bocquet, and R. R. Netz, Phys. Rev. Lett. 103, 144503

(2009).

⁷J.S. Hansen, H. Bruus, B.D. Todd, and P.J. Daivis. J. Chem. Phys. 133, 144906 (2010).

⁸S. De Luca, B.D. Todd, J.S. Hansen and P.J. Daivis, J. Chem. Phys. 138, 154712 (2013)