Professor Irmgard Bischofberger

Why is there so much structure, order and texture to life and nature, rather than a featureless expanse? From microscopic snowflakes to dried mud and large-scale river networks, pattern formation leads to systems of extraordinary intricacy and beauty. Understanding how a system spontaneously selects its overall structure remains an ongoing engineering and scientific challenge. In this talk, I will briefly outline my lab’s recent successes in identifying the underlying mechanisms of pattern selection in a large range of complex fluids, which has allowed us to developed strategies to control unstable growth. I will then discuss two examples of how intricate structuring emerges. In evaporating drops of aqueous nanoparticle suspensions, we report the dynamics of crack formation and the fracture morphology. We show that in the final stage of drying, the remaining stresses in the nanoparticle deposit can be released in two distinct ways: by bending out of plane or by forming a second generation of orthoradial cracks. In a second example, we report the surprising emergence of chiral domains in a flowing nematic liquid crystal despite the achiral nature of the material. The chirality results from a periodic double-twist deformation of the liquid crystal and leads to striking stripe patterns vertical to the flow direction. Finally, I will discuss how understanding pattern selection allows us to tune the mechanical properties of soft composite materials.