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Roberto PIAZZA - Italie

On the footsteps of Perrin : Settled, unsettled, and unsettling issues in particle settling.

Colloid sedimentation has played a seminal role in the development of statistical physics thanks to the celebrated experiments by Perrin, which provided a concrete demonstration of molecular reality and gave strong support to Einstein’s theory of Brownian motion. My talk, which mostly focuses on particle settling in conditions where Brownian fluctuations are dominant (low Peclét number), aims to show that a lot more can be learnt both from the sedimentation equilibrium and from the particle settling dynamics of a wide class of systems, ranging from simple colloids to emulsions and foams, from colloidal gels to active particles and living organisms. In particular, equilibrium sedimentation profiles provide in a single measurement the whole equation of state and the entire phase diagram of model systems such as hard, sticky, and charged spheres, whereas a chaotic microscopic dynamics, dominated by wild hydrodynamics fluctuations results, rather surprisingly, in a slow, regular macroscopic settling kinetics. At the same time, the occurrence of unexpected and surprising effects, which may even challenge the Archimedes’ principle, arguably one of the oldest laws of physics, brings about relevant questions in statistical and fluid mechanics that make sedimentation an exciting field of research.



Roberto Piazza is Professor of Condensed Matter Physics at the Department of Chemistry & Material Science at the Politecnico di Milano in Italy. He is known for his contributions and his passion for Soft Matter Science, both of which he has recently channeled in the book “Soft Matter – the stuff that dreams are made of”. His particular interests are devoted to different aspects of colloid science, increasingly at the interface with biophysics. He is section editor for “Liquids, Soft Matter, and Biological Physics” of the Journal of Physics : Condensed Matter. Roberto’s scientific work is accompanied by an interest in the history of science and by educated glances into the star-lit sky.