Spotlight
Mark Buckley
Mark Buckley is a graduate student who studies colloidal suspensions with the Itai Cohen Group on Complex Matter Physics. "When you shear a colloidal suspension quickly its viscosity increases by orders of magnitude more than when it's being perturbed more slowly," says Buckley. "It's like cornstarch mixed with water: when you move your finger through it slowly it's thin like water, but if you move your finger though it quickly it's thick like an elastic solid. The micron-sized particles we study also behave this way."
Buckley sandwiches his test samples in a "shear cell," a mechanism with a small piezo motor on the bottom plate and a silicon chip on the top. He uses a confocal microscope to raster through a sample and reconstruct an image in three dimensions. With these tools he can look at the microstructural changes that are occurring in the shear thickening regions.
Where are these experiments leading? "We can use these same techniques to study the shear mechanical properties of articular cartilage, the substance that coats our bones and joints," says Buckley. "Cartilage is designed by nature to withstand large shear and other stresses. The microstructure of cartilage is very complex. How does the underlying microstructure of cartilage affect its macroscopic properties? By studying real tissue we may someday figure out how to make replacement tissue."