Liquid–solid-like transition in quasi-one-dimensional driven granular media

Abstract

The theory of non-ideal gases at thermodynamic equilibrium, for instance the van der Waals gas model, has played a central role in our understanding of coexisting phases, as well as the transitions between them. In contrast, the theory fails with granular matter because collisions between the grains dissipate energy, and their macroscopic size renders thermal fluctuations negligible. When a mass of grains is subjected to mechanical vibration, it can make a transition to a fluid state. In this state, granular matter exhibits patterns and instabilities that resemble those of molecular fluids. Here, we report a granular solid–liquid phase transition in a vibrating granular monolayer. Unexpectedly, the transition is mediated by waves and is triggered by a negative compressibility, as for van der Waals phase coexistence, although the system does not satisfy the hypotheses used to understand atomic systems. The dynamic behaviour that we observe—coalescence, coagulation and wave propagation—is common to a wide class of phase transitions. We have combined experimental, numerical and theoretical studies to build a theoretical framework for this transition. Our tools for understanding phase transitions at thermal equilibrium do not usually apply to granular matter. However, a vibrating quasi-one-dimensional system displays dynamic behaviour common to classic phase transitions.