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Séminaire LMFA (présentiel - INSA) : Bubble dynamics in Yield-Stress Fluids

Le 14 octobre 2022

INSA, Bât. J. Ferrand, Amphi Royer

Langue / language: the presentation will be in English

Présenté par : Brice Saint-Michel - Université Gustave Eiffel

Brice Saint-Michel - Université Gustave Eiffel

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Bubbles inclusions are intentionally added or naturally present in many complex fluids and soft materials. They reduce the carbon footprint and improve the thermal insulation performances of concrete, they grow and rise in anaerobic digestion sludges and confer ice-creams and doughs a smooth, light texture. In contrast with solid particles, bubbles are not entirely passive in their environment : small individual bubbles (100 µm) dissolve and also react to an acoustic excitation by undergoing volumetric oscillations. The resonance parameters of these oscillations depend on the bubble environment. In return, bubbles in fluid matrices confer remarkable acoustic properties.

Bubble dynamics has been mostly investigated in Newtonian fluids and hydrogels (agar, gelatin) in the biomedical field, e.g. to understand the role of cavitation in traumatic brain injury. In contrast, it has only been marginally studied in yield-stress fluids despite the ease with which bubbles are injected and retained in such materials and its biological and industrial relevance. In addition, the interplay between bubble dynamics and the yield stress leads – in theory – to rich physics : dissolution may or may not be arrested depending on the matrix properties ; bubble oscillation dynamics could be used as high-frequency rheological probes across the yielding transition ; and oscillations could trigger bubble release. Acoustic radiation forces might also be used to directly move bubbles in these materials.

In this presentation, we examine bubble dynamics in yield-stress fluids chiefly through experiments. We compare theoretical predictions for dissolution and oscillations with experiments conducted in a standard Carbopol microgel. I examine the potential of using single bubbles as rheological probes in yield-stress fluids. I finally discuss the possibility of using bubble pairs to further examine the high-frequency, non-linear rheology of these materials.