Non-monotonic variation of viscous dissipation in confined liquid films: A reconciliation

¹ Physics of Complex Fluids, MESA+ Institute for Nanotechnology, Department of Science and Technology, University of Twente - P.O. Box 277, 7500 AE Enschede, The Netherlands, EU
² Computational BioPhysics, MESA+ Institute for Nanotechnology, Department of Science and Technology, University of Twente P.O. Box 217, 7500 AE Enschede, The Netherlands, EU

^a s.j.a.debeer@utwente.nl
^b w.k.denotter@utwente.nl
^c h.t.m.vandenende@utwente.nl
^d w.j.briels@utwente.nl
^e f.mugele@utwente.nl

Received: 19 October 2011
Accepted: 9 January 2012

Abstract

Viscous dissipation in highly anisotropic confined liquids is at the moment heavily debated due to conflicting results from different experiments. We report molecular-dynamics simulations of such confined liquids in a geometry mimicking atomic force microscopy experiments. Using a novel approach based on the analysis of force fluctuations and the fluctuation-dissipation theorem, we extract the damping coefficient for the normal motion of the tip. Our results reveal the existence of peaks of excess dissipation at intermediate gap widths between n and n+1 molecular layers, in agreement with recent experiments. The observed correlation between these peaks and the decreased order in the films provides a microscopic interpretation of these experimental results.