Short Time-scale Colloidal Motion in Complex Materials

How do the macroscopic properties of materials derive from their microscopic interactions? For simple fluids the Navier-Stokes equations allow us to connect the micro-scale and the macro-scale. By contrast, drawing the connection between the local structure of a complex fluid and the global response is extremely difficult. We demonstrate a technique to examine a tracer particle at very short time and length scales as a probe on the properties of the carrier fluid, be it simple newtonian fluid, a more complex Maxwell fluid, or even a colloidal glass. By examining the thermal motion of a freely moving colloid we can uncover both the local structure of the material and the global state properties. We report on the verification of the Clercx-Schram law for dense fluids, a violation of the expected behavior of Maxwell fluids, and new results in the micro-scale behavior of colloidal glasses.