Bulk-like viscosity and shear thinning during dynamic compression of a nanoconfined liquid

Abstract

The viscosity of liquids under nanoconfinement remains controversial. Reports range from spontaneous solidification to no change in the viscosity at all. Here, we present thorough measurements with a small-amplitude linear atomic force microscopy technique and careful consideration of the confinement geometry, to show that in a weakly interacting liquid, average viscosity remains bulk like, except for strong shear thinning once the liquid is confined to less than four molecular layers. Overlaid over this bulk-like viscous behavior are stiffness and damping oscillations, indicating non-continuum behavior, as well as an elastic response when the liquid is allowed to order in the confinement gap.