  The flow of water confined to nanometer-sized pores is central to a wide
range of subjects from biology to nanofluidic devices. Despite its importance,
a clear picture about nanoscale fluid dynamics is yet to emerge. Here we
measured dissipation in less than 20 nm thick water films and it was found to
decrease for both wetting and non-wetting confining surfaces. The fitting of
Carreau-Yasuda model of shear thinning to our measurements implies that flow is
non-Newtonian and for wetting surfaces the no-slip boundary condition is valid.
On the contrary, for non-wetting surfaces boundary slippage occurs with slip
lengths of the order of few nm. The findings suggest that both, the wettability
of the confining surfaces and nonlinear rheological response of water molecules
under nano-confinement play a dominant role in transport properties.
