blair lab at georgetown

Stress propagation in silica glasses

colloid image raw How do forces propagate and how are they distributed within soft materials?  In granular materials the answer to this questions is well known.  However, for the case of colloidal hard spheres, an answer remains ellusive.

The objective of this project is to understand how colloidal glasses distribute and bear external stress. We seek to measure the distribution of forces at the boundaries of “glassy” colloidal silica, using confocal rheology.  Our method is based on the application of a controlled shear stress to a “glassy” colloidal silica sample. The sample is composed of bidisperse silica colloids in a dyed index matching solvent.   The shear force is applied using a rheometer (Anton Paar MCR 301) with cone and plate geometry. Using a technique similar to traction force microscopy, we observe the local force distribution at the boundary of the glass.