Granular materials pervade our everyday life (coffee, flours, sand, etc.) and industrial processes at all technological levels (cereal storage, concrete production, extraction of minerals/oils/gases from soils, powder treatment and transport, pharmaceutical and chemical/combustion systems, etc.). Understanding granular materials also impacts the analysis and prevention of environmental and geophysical hazards.
On the side of fundamental research, granular materials represent a unique test ground for the most recent theories in the statistical physics of non-equilibrium systems. The interaction of macroscopic grains with themselves and with the environment involve dissipative processes, mainly friction along normal and sliding modes, which play a crucial role in the theoretical modelling and marks a striking difference with respect to the molecular phases of matter. In very idealised situations or clean theoretical models one can still find signatures of granular gases, liquids and solids, but in real situations (even in controlled experiments) the boundary between phases is blurred by large fluctuations, heterogeneities, strong currents and other anomalies which require new approaches and theories.
General theories for non-equilibrium statistical physics, for most of the 20th century, have been dominated by close-to-equilibrium (or linear) phenomena. Two renowned (and interrelated) examples are the Equilibrium Fluctuation-Dissipation theorem and the so-called Linear Irreversible Thermodynamics. In other fields, for instance in fluid-dynamics and turbulence or in dynamical systems, the far-from-equilibrium situation was the rule but the approach was rather specific and rarely interested to retrieve possibly universal relations. In the last 20 years a series of new results in stochastic thermodynamics has opened the way to rationalise non-equilibrium phenomena in a possibly more universal or widely applicable framework . Those result include, for instance, the generalisation of linear response theory to non-equilibrium steady states, as well as the so-called Fluctuation Relations which embrace fully non-linear aspects (large deviations) of the fluctuations of currents.
Our group based at the Sapienza unit of the Institute for Complex Systems is involved in all the aforementioned aspects of the frontier of statistical physics, with a special focus on numerical simulations and experiments in the slow and fast dynamics of granular matter and other complex fluids. This page is devoted to discuss a few representative results of our recent activity.