Viscous dissipation in molecularly thin liquid films

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In this project, we want to study the viscosity and the flow properties in thin liquid films confined between atomically smooth surfaces at a separation of the order of a few molecular diameters. In contrast to bulk liquids, which are isotropic, the molecules in such confined liquid layers are arranged in layers parallel to the interfaces. Typically, this layer structure extends a few molecular diameters into the liquid phase. The goal of the present project is to determine how the viscosity of liquids is affected by this structural rearrangement within a few nanometers of the solid-liquid interface. In order to study these phenomena, we use two different extensions of the so-called Surface Forces Apparatus (SFA). The first one, which was developed recently in our laboratory, allows for direct video imaging of hydrodynamic processes at the molecular level. The second one is a combination of the SFA with fluorescence microscopy techniques, in particular fluorescence recovery after photobleaching (FRAP). In this case, fluorescent molecules are used to decorate flow patterns within the confined liquid layers.