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Issue 12, 2019
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A mesoscale study of creep in a microgel using the acoustic radiation force

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Abstract

We study the motion of a sphere of diameter 330 μm embedded in a Carbopol microgel under the effect of the acoustic radiation pressure exerted by a focused ultrasonic field. The sphere motion within the microgel is tracked using videomicroscopy and compared to conventional creep and recovery measurements performed with a rheometer. We find that under moderate ultrasonic intensities, the sphere creeps as a power law of time with an exponent α ≃ 0.2 that is significantly smaller than the one inferred from global creep measurements below the yield stress of the microgel (α ≃ 0.4). Moreover, the sphere relaxation motion after creep and the global recovery are respectively consistent with these two different exponents. By allowing a rheological characterization at the scale of the sphere with forces of the order of micronewtons, the present experiments pave the way for acoustic “mesorheology” which probes volumes and forces an intermediate between standard macroscopic rheology and classical microrheology. They also open new questions about the effects of the geometry of the deformation field and of the sphere size and surface properties on the creep behaviour of soft materials.

Graphical abstract: A mesoscale study of creep in a microgel using the acoustic radiation force

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Article information


Submitted
09 Nov 2018
Accepted
19 Feb 2019
First published
25 Feb 2019

Soft Matter, 2019,15, 2688-2702
Article type
Paper

A mesoscale study of creep in a microgel using the acoustic radiation force

P. Lidon, L. Villa and S. Manneville, Soft Matter, 2019, 15, 2688
DOI: 10.1039/C8SM02294A

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