Shock driven jamming and periodic fracture of particulate rafts

Abstract

A tenuous monolayer of hydrophobic particles at the air-water interface often forms a scum or raft. When such a monolayer is disturbed by the localized introduction of a surfactant droplet, a radially divergent surfactant shock front emanates from the surfactant origin and packs the particles into a jammed, compact, annular band with a packing fraction that saturates at a peak packing fraction ${\varphi }^{\ast }$. As the resulting two-dimensional, disordered elastic band grows with time and is driven radially outwards by the surfactant, it fractures to form periodic triangular cracks with robust geometrical features. We find the number of cracks $N$ and the compaction band radius $R^{\ast }$ at fracture onset vary monotonically with the initial packing fraction (${\varphi }_{init}$). However, its width $W^{\ast }$ is constant for all ${\varphi }_{init}$. A simple geometric theory that treats the compaction band as an elastic annulus, and accounts for mass conservation allows us to deduce that $N\simeq 2\pi R^{\ast }/W^{\ast }\simeq 4\pi {\varphi }_{RCP}/{\varphi }_{init}$, a result we verify both experimentally and numerically. We show the essential ingredients for this phenomenon are an initially low enough particulate packing fraction that allows surfactant driven advection to cause passive jamming and eventual fracture of the hydrophobic particulate interface.

6 Pages, 4 figures. To appear in Europhysics Letters

References in corpus (5)

• Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
• Elasticity of an interfacial particle raft
• Granular Character of Particle Rafts
• Surfactant Driven Fracture of Interfacial Particle Rafts
• Instabilities in droplets spreading on gels

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• Elasto-capillary interaction of particles on the surfaces of ultra-soft gels: a novel route to study self-assembly and soft lubrication
• Strain localization and failure of disordered particle rafts with tunable ductility during tensile deformation
• Cluster Formation and Relaxation in Particle Rafts under Uniform Radial Expansion