Imaging and rheology of colloidal glasses under steady shear
- Event time: 1:00pm
- Event date: 20th November 2006
- 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
Steady shear of a colloidal hard sphere glass can be considered one of the simplest examples of nonlinear rheology of soft glassy materials. In this talk I will discuss the results of two series of experiments on sheared hard sphere glasses. In the first, we measure the steady state flow curve of the suspension using a rheometer while simultaneously imaging the flow profile via a coupled-in confocal microscope. The results show that measured flow curves do not represent a uniform shear rate in the system but instead the glassy samples exhibit marked shear localization with the size of un-sheared regions growing on reducing shear rate or increasing volume fraction. The second experiment focuses on microscopic particle dynamics in regions of linear shear. With particle tracking, both local shear rate and structural relaxation time in these regions are measured directly, which allows inferring a microscopic stress-strainrate relation. The apparent difference between the macroscopic and microscopic flow-curve is discussed, along with scenarios to reconcile the two measurements.
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..