Nonspherical armoured bubble vibration

Abstract

In this paper, we study the dynamics of cylindrical armoured bubbles excited by mechanical vibrations. A step by step transition from cylindrical to spherical shape is reported as the intensity of the vibration is increased, leading to a reduction of the bubble surface and a dissemination of the excess particles. We demonstrate through energy balance that nonspherical armoured bubbles constitute a metastable state. The vibration instills the activation energy necessary for the bubble to return to its least energetic stable state: a spherical armoured bubble. At this point, particle desorption can only be achieved through higher amplitude of excitation required to overcome capillary retention forces. Nonspherical armoured bubbles open perspectives for tailored localized particle dissemination with limited excitation power.

Buckling vs. particle desorption in a particle-covered drop subject to compressive surface stresses: a simulation study

“…The results of the current work are valid for quasi-static situations. Experiments report buckling and particle expulsion in highly-dynamic situations in which time-dependent pressure fields change the shape of particle-covered bubbles 1,44 . In these situations both the particle and the fluid inertia are important.…”

Capillary interactions between dynamically forced particles adsorbed at a planar interface and on a bubble

“…At small inter-particle separations, the lateral force can be repulsive, and therefore the critical separation distance for particle aggregation on a bubble is significantly decreased by dynamic effects. Dynamic capillary interactions between colloidal particles oscillating at an interface have not yet been observed, likely because of the high surface coverage in typical experiments, resulting in small inter-particle distances such that this theory is not applicable (Poulichet & Garbin 2015; Prabhudesai et al 2017). This work therefore motivates future controlled experiments with sufficiently large inter-particle distances.…”

“…Protière et al (2006, 2005) and Moláček & Bush (2013) found that the interactions between drops bouncing on an interface and the capillary waves generated during each impact are responsible for a range of drop dynamics such as inter-drop attraction, repulsion and orbiting. Dynamic capillary interactions could be relevant for the self-assembly of colloids on the interface bubbles and drops deformed by unsteady and dynamic stresses (Mulligan & Rothstein 2011; Poulichet & Garbin 2015; Prabhudesai et al 2017).…”

Collapse mechanisms and extreme deformation of particle-laden interfaces

“…Interestingly, upon highly dynamic deformation, particle expulsion occurs even for initially cohesive monolayers, because the mechanical energy input to the monolayer is sufficient to re-disperse the particles on the interface [74]. On a larger scale, millimetric particle-coated bubbles with initial anisotropic shapes were found to relax to their equilibrium spherical shape when vibrated, with the excess particles expelled in the surrounding liquid [76].…”