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Acoustic bubble dynamics in a yield-stress fluid

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Abstract

Yield-stress fluids naturally trap small bubbles when their buoyancy applies an insufficient stress to induce local yielding of the material. Under acoustic excitation, trapped bubbles can be driven into volumetric oscillations and apply an additional local strain and stress that can trigger yielding and assist their release. In this paper we explore different regimes of microbubble oscillation and translation driven by an ultrasound field in a model yield-stress fluid, a Carbopol microgel. We first analyse the linear bubble oscillation dynamics to measure the local, high-frequency viscosity of the material. We then use acoustic pressure gradients to induce bubble translation and examine the elastic part of the response of the material below yielding. We find that, at moderate pressure amplitude, the additional stresses applied by volumetric oscillations and acoustic radiation forces do not lead to any detectable irreversible bubble motion. At high pressure amplitude, we observe non-spherical shape oscillations that result in erratic bubble motion. The critical pressures we observe differ from the predictions of a recent model of shape oscillations in soft solids. Based on our findings, we discuss possible reasons for the lack of bubble release in Carbopol and suggest other systems in which ultrasound-assisted bubble rise may be observed.

Graphical abstract: Acoustic bubble dynamics in a yield-stress fluid

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Article information


Submitted
04 Jun 2020
Accepted
30 Sep 2020
First published
13 Oct 2020

This article is Open Access

Soft Matter, 2020, Advance Article
Article type
Paper

Acoustic bubble dynamics in a yield-stress fluid

B. Saint-Michel and V. Garbin, Soft Matter, 2020, Advance Article , DOI: 10.1039/D0SM01044H

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