Thomas Becker, University of Ulm, Germany, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the internanotech Community at http://nanotech.colayer.net/
Nanofluidics: Molecularly thin lubricant layers under confinement
Confined liquid films with a thickness in the range of a few molecular diameters exhibit different mechanical properties than in the bulk. With the technique of a 2-dimensional imaging Surface Force Apparatus we investigated in detail the layer by layer thinning of a confined thin liquid film with increasing external normal force on the substrates. The dynamics of the boundary line of the layering transitions were analyzed and we found good agreement with a simple hydrodynamic model. While it is generally accepted that the viscosity of confined liquids increases with decreasing thickness, the order of magnitude is highly debated. Using ultraclean, recleaved mica surfaces in our measurements, we find that the viscosity of the model lubricant Octamethylcyclotetrasiloxane (OMCTS) increases by a factor of 10 with decreasing the film thickness from 6 to 2 layers. Using a new hydrodynamic model, we show that the sliding friction of liquid layers on top of the solid substrates is approximately 30 times higher than the mutual friction between adjacent liquid layers. The latter was independent of film thickness and in close agreement with the bulk viscosity. The mentioned variations in mechanical properties of thin liquid films compared with the bulk arise from structural changes. Making use of recent advances in synchrotron radiation sources and beam shaping techniques allow scattering experiments to investigate the in-plane structure of confined liquids. We present here preliminary x-ray scattering data from a thin film of confined liquid crystalline 8CB and we discuss the domain structure of the liquid crystal and the anchoring of the liquid crystal with respect to the mica lattice.