Realtime 3D microscopy of colloidal glasses under shear
- Event time: 1:00pm
- Event date: 7th November 2005
- Speaker: Rut Besseling (Formerly School of Physics & Astronomy, University of Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
Colloidal glasses exhibit a range of interesting phenomena when submitted to shear. Like molecular glasses, despite the liquid-like microstructure, they respond elastically and reversibly when submitted to small stress or strain. For larger stress, yielding and plastic flow occur, associated with breaking of the neighbor cages, recently discussed by K. Pham in relation to rheological measurements. Other phenomena include coexistence of plastically moving and solid regions (shearbanding) and the restoring of ergodicity in the glass by shear flow. In this talk I will discuss recent results of realtime 3D imaging and tracking of colloidal glasses under slow oscillatory and steady shear. After an explanation of the experimental and analysis techniques involved, I will first illustrate the occurrence of shearbanding in hard sphere glasses. Next, I will discuss measurements under oscillatory shear. Ensemble average quantities (e.g. mean squared displacements) show a crossover from subdiffusive, quasi-reversible behavior to diffusive, irreversible behavior (yielding) when the strain amplitude is increased from ~5% to 20%. However, on the microscopic level we find that the local distortions and their reversibility show pronounced spatial variations, associated with the heterogeneity of the cages. Finally, I will discuss the decay of correlation functions under steady shear, showing that the effect of shear is similar to melting the glass by lowering the volume fraction.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..