Monday, December 4th, 11h30, Room 454 A, Condorcet Building.

Brice Saint-Michel

 Laboratoire Navier, Université Gustave Eiffel/CNRS/ENPC, Champs sur Marne, France

Bubble dynamics in yield-stress fluids

Brice Saint-Michel¹ and Valeria Garbin²

¹ Laboratoire Navier, Université Gustave Eiffel/CNRS/ENPC, Champs sur Marne, France
² Transport Phenomena, Department of Chemical Engineering, Delft University of Technology, the Netherlands

Bubbles are intentionally added or naturally present in many complex fluids and soft materials, notably yield-stress fluids, in which they remain trapped [1]. Bubbles reduce the carbon footprint and improve the thermal insulation performances of concrete and confer ice-creams and doughs a smooth, light texture, and their rise is a critical issue in anaerobic digestion. They are not passive in their environment: small individual bubbles (100 µm) dissolve in fluids, whereas they undergo volumetric oscillations under an acoustic field [2]. Complex bubbly media are subject to Ostwald ripening and possess remarkable acoustic properties [3]. All of these phenomena are influenced by the mechanical properties of the matrix surrounding the bubbles ; yet, bubble dynamics has been mostly investigated in Newtonian fluids and hydrogels (agar, gelatin) in the biomedical field [4]. 

Despite potentially rich physics, bubble dynamics studies in yield-stress fluids is mostly limited to bubble rise [1]. In this presentation, we examine in experiments  the dynamics of individual – or pairs of – bubbles in this class of fluids, for the case of bubble dissolution, quasistatic inflation and volumetric oscillations under ultrasound [5,6]. We question whether we can use these processes to probe the mechanical properties of the matrix; we also discuss whether dissolution [7] and activated release under ultrasound [6] are possible. 

Left: Successive snapshots of bubble dissolution in a transparent yield-stress fluid. Centre: Two superposed snapshots of bubble inflation in the same yield-stress fluid using a needle. Right: Successive snapshots of bubbles in a yield stress fluid undergoing parametric shape instability under the application of ultrasound. Scale bars are respectively 200 µm, 4 mm and 300 µm.

References : 
[1] J. Tsamopoulos et al., J. Fluid Mech. 601, 123-164 (2008)
[2] T. J. Leighton, The Acoustic Bubble, Academic Press (1997) 
[3] V. Leroy et al., Phys. Rev. B. 91, 020301 (2015)
[4] C. Barney et al., Proc. Natl. Acad. Sci. U. S. A. 117, 9157-9165 (2020)
[5] M. de Corato et al., Phys. Rev. Fluids 4, 073301 (2019)
[6] B. Saint-Michel and V. Garbin, Soft Matt. 18, 10405-10418 (2020)
[7] D. Venerus, J. NonNewton. Fluid Mech., 215, 53-59 (2015)

À lire aussi