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Physics of Packing : From Hard Spheres to Hydrogels

The spatial arrangement of particles in ordered and disordered arrays play a key role in a large number of areas including coding theory, glass and jamming transition and the intriguing phenomena of shear thickening.  In the first part of the talk I will present recent work on the phenomenon of shear thickening (including the interesting effect of running on cornstarch suspensions) and how impacting a shear thickening suspension has similarities to rapid quenching in a conventional condensed matter system. Impacting a shear thickening system creates a transient solid which then relaxes back to a liquid state. I will then present some recent techniques we have developed using quantum dots allowing us to probe the internal dynamics in a hard sphere system. The second part of the talk will go beyond hard sphere systems and present work on hydrogel systems to show how deformability of the particles changes the conventional paradigm of hard sphere systems and opens up an entirely new area in soft matter physics. Complete three dimensional imaging in hydrogel systems allow us to probe, for the first time, internal stresses and flow fields which are of great importance in areas like fracking, carbon sequestration and instabilities in porous media flows.