Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Surface fluctuations or How to measure properties of soft matter systems without contact

The free surface of any liquid or solid at rest keeps deforming under the action of thermal agitation. Measurements of surface fluctuations can provide information on the properties (in particular mechanical) of the material, in a fully non invasive way. We have developed an optical method to measure the surface waves resulting from thermal motion in liquids and soft solids. I will show that linear viscoelasticity can be fully characterized in a wide frequency range using that method, which is particularly relevant for multi scale soft matter or biological systems. I will further detail how surface fluctuation measurements can be used to probe the dynamics of a liquid at molecular distances from a solid wall. We have in particular evidenced that at vanishing flows a nanometric solid-like layer close to the wall may form in some liquids.