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Dynamic AFM : Nano-Rheology of Confined Fluids
In this talk I will present a study of the atomic force microscope (AFM) in liquid medium and its application to the study of the rheology of confined fluids. We will see that the AFM allows not only to image the surface of a substrate but also to measure the properties of the medium that is confined between the tip and the substrate. If the medium is a fluid, its rheological properties can be studied on scales ranging from nanometer to several micrometers by varying the gap (distance). Using the AFM we have performed a sensitive measurement of the dissipation and the effective viscosity of a simple confined liquid (octamethylcyclotetrasiloxane). The experimental data show that the damping and the effective viscosity increase and present oscillations as the gap between the cantilever tip and the surface is diminished. Such an experimental result is different from what has been reported earlier where only a continuous increase of the damping and the viscosity are observed. Then I will describe the study of the flow of fluids (water and air) close to solid surfaces using a dynamic AFM. I will present our measurement method and different slip length values extracted from our experimental data for water and air on different surfaces. Our measurement method shows that we are able to measure as small slip length value as 8nm. I will also presents our preliminary results on the contact line friction extracted from the shape bubble vibration measured by the AFM.