1 research outputs found
Wall slip of complex fluids: interfacial friction or slip length?
Using a dynamic Surface Force Apparatus, we demonstrate that the notion of
slip length used to describe the boundary flow of simple liquids, is not
appropriate for viscoelastic liquids. Rather, the appropriate description lies
in the original Navier's partial slip boundary condition, formulated in terms
of an interfacial friction coefficient. We establish an exact analytical
expression to extract the interfacial friction coefficient from oscillatory
drainage forces between a sphere and a plane, suitable for dynamic SFA or
Atomic Force Microscopy non-contact measurements. We use this model to
investigate the boundary friction of viscoelastic polymer solutions over 5
decades of film thicknesses and one decade in frequency. The proper use of the
original Navier's condition describes accurately the complex hydrodynamic force
up to scales of tens of micrometers, with a simple "Newtonian-like" friction
coefficient, not frequency dependent, and reflecting closely the dynamics of an
interfacial depletion layer at the solution/solid interface.Comment: 7 pages, 5 figure