Densely-packed particle raft at vertically vibrated air-water interface

TL;DR

This study explores the complex behaviors of a dense particle raft at a vibrated air-water interface, revealing pattern formation, elasticity changes, glassy dynamics, and cavitation phenomena influenced by vibration parameters.

Contribution

It provides new insights into the interplay between vibration-induced patterns, elasticity, and particle dynamics in dense granular rafts at fluid interfaces.

Findings

Classical standing wave instability observed at certain parameters.

Increased packing fraction enhances raft elasticity and reduces surface tension.

Cavitation occurs at high vibration amplitudes, creating coexistence of water waves and particle motion.

Abstract

We investigate the dynamics of a dense raft of millimeter-sized granular particles at a vertically vibrated air-water interface, which displays a rich set of patterns and particle dynamics as we vary the vibration amplitude, frequency, and particle packing fraction. While the classical parametric instability with standing waves still occurs over a certain parameter space, the measured wave dispersion relations indicate an increasing role in the raft's emerging elasticity at higher packing fractions, which induces a decrease in the effective surface tension and an increase in an out-of-plane bending modulus. At higher vibration frequencies and lower amplitudes, we also identified a regime without standing waves in which individual particles exhibit thermal-like motion and transition from diffusive to sub-diffusive transport as the packing fraction increases. Glassy behaviors such as spatial and temporal heterogeneity in particle dynamics occur as well, which is analogous to supercooled liquids. When the vibration amplitude is increased starting in this supercooled regime, a large cavity eventually forms inside the raft with its size and shape related to the vibration frequency and the injected vibration energy. The cavitation results in the coexistence of free surface water waves inside the cavity and thermal-like particle motion in the raft.