Thermodynamic dependences of slip length for nanofluidic flows over crystalline surfaces: Predictions of molecular theory of solvation

Abstract

AbstractWe study the pressure and temperature dependence of the hydrodynamic slip length for the laminar flow of water near the crystalline surfaces of gold, copper, and nickel by the methods of nonequilibrium statistical mechanics. This study is further development of our previous work on formulation of the molecular theory of hydrodynamic (slip) boundary conditions in nanofluidics. Phenomenological picture relates slip length to viscosity of the liquid, and establishes the direct proportionality among them. Any difference between this phenomenological approach and measurements could not be explained, unless one uses the molecular theory of liquids and an appropriate atomistic model for surface corrugation. To vindicate the anomaly, we refer to the notion of formation and rupture of the hydrogen bond network in water. To verify this hypothesis, we apply the theory and perform calculations in the entire range of temperatures for the stable liquid phase and for pressures up to 100 MPa. The variation found in the slip length is of two orders of magnitude, which is much more than the variation in the viscosity alone. We validate our concept by referring to observable changes in the liquid microscopic structure and relating them with the theory. The information obtained is relevant for rational design of new MEMS/NEMS devices. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009