Issue 18, 2016

Surface waves on a soft viscoelastic layer produced by an oscillating microbubble

Abstract

Ultrasound-driven bubbles can cause significant deformation of soft viscoelastic layers, for instance in surface cleaning and biomedical applications. The effect of the viscoelastic properties of a boundary on the bubble–boundary interaction has been explored only qualitatively, and remains poorly understood. We investigate the dynamic deformation of a viscoelastic layer induced by the volumetric oscillations of an ultrasound-driven microbubble. High-speed video microscopy is used to observe the deformation produced by a bubble oscillating at 17–20 kHz in contact with the surface of a hydrogel. The localised oscillating pressure applied by the bubble generates surface elastic (Rayleigh) waves on the gel, characterised by elliptical particle trajectories. The tilt angle of the elliptical trajectories varies with increasing distance from the bubble. Unexpectedly, the direction of rotation of the surface elements on the elliptical trajectories shifts from prograde to retrograde at a distance from the bubble that depends on the viscoelastic properties of the gel. To explain these behaviours, we develop a simple three-dimensional model for the deformation of a viscoelastic solid by a localised oscillating force. By using as input for the model the values of the shear modulus obtained from the propagation velocity of the Rayleigh waves, we find good qualitative agreement with the experimental observations.

Graphical abstract: Surface waves on a soft viscoelastic layer produced by an oscillating microbubble

Article information

Article type
Paper
Submitted
21 Dec 2015
Accepted
07 Apr 2016
First published
07 Apr 2016
This article is Open Access
Creative Commons BY license

Soft Matter, 2016,12, 4247-4256

Surface waves on a soft viscoelastic layer produced by an oscillating microbubble

M. Tinguely, M. G. Hennessy, A. Pommella, O. K. Matar and V. Garbin, Soft Matter, 2016, 12, 4247 DOI: 10.1039/C5SM03084F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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