Geometry-controlled phase transition in vibrated granular media

TL;DR

This study investigates how modifying container geometry influences phase transitions and agitation in vibrated granular media, revealing geometry-induced effects on solid-fluid coexistence and melting behavior.

Contribution

It demonstrates that container asymmetry controls phase coexistence and defect formation, linking geometry to granular melting transitions in vibrated systems.

Findings

Container geometry affects solid-fluid volume ratio.

Defect density correlates with granular temperature.

Geometry influences melting transition via topological defects.

Abstract

We report experiments on the dynamics of vibrated particles constrained in a two-dimensional vertical container, motivated by the following question: how to get the most out of a given external vibration to maximize internal disorder (e.g. to blend particles) and agitation (e.g. to absorb vibrations)? Granular media are analogs to classical thermodynamic systems, where the injection of energy can be achieved by shaking them: fluidization arises by tuning either the amplitude or the frequency of the oscillations. Alternatively, we explore what happens when another feature, the container geometry, is modified while keeping constant the energy injection. Our method consists in modifying the container base into a V-shape to break the symmetries of the inner particulate arrangement. The lattice contains a compact hexagonal solid-like crystalline phase coexisting with a loose amorphous fluid-like phase, at any thermal agitation. We show that both the solid-to-fluid volume fraction and the granular temperature depend not only on the external vibration but also on the number of topological defects triggered by the asymmetry of the container. The former relies on the statistics of the energy fluctuations and the latter is consistent with a two-dimensional melting transition described by the KTHNY theory.