ON THE NATURE OF SHEAR THINNING IN NANOSCOPICALLY CONFINED FILMS

Non-Equilibrium Molecular Dynamics (NEMD) computer simulations were em ployed to study films in nanometer confinements under shear. Focusing on the response of the viscosity, we found that nearly all the shear t hinning takes place inside the solid-oligomer interface and that the a dsorbed layers are more viscous than the middle part of the films. Mor eover, the shear thinning inside the interfacial area is determined by the wall affinity and is largely insensitive to changes of the film t hickness and the molecular architecture. The rheological response of t he whole film is the weighted average of these two regions -''viscous' ' interfacial layer and bulk-like middle part- resulting in an absence of a universal response in the shear thinning regime, in agreement wi th recent SFA experiments of fluid lubricants.