The Shear Excitement of Confined Colloidal Suspensions Itai Cohen Weitz Group Gordon Mckay Lab Harvard University We have built a shear cell which can be loaded onto a confocal microscope thus allowing us to image the microstructure of a dense colloidal suspension when it is subjected to an imposed oscillatory strain. When the gap between the shearing plates accommodates less than 11 particle layers, the suspension forms a beautiful buckled pattern which is not observed in bulk. The particles in the shear zone are in contact with a reservoir of unsheared particles. In this talk I will show that the osmotic pressure of the particles in the reservoir plays a fundamental role in the formation of the buckled pattern adopted by the particles in the shear zone. I will then discuss how to use the lessons learned from such observations more generally in studying colloidal suspensions under shear.