Growth and stability of bubbles in a yield stress fluid

Abstract

Experiments are reported that explore the onset of motion of bubbles in a model yield stress fluid, Carbopol gel. Starting from a trapped spherical bubble in a gel, the yielding limit for the bubble motion is obtained by gradually expanding the bubble via a stepwise decrease in pressure. Our results show that at the yielding limit bubbles are longer and thinner when they are in a higher concentrated gel. This is suggestive of a link between the shape and size of the bubbles at the onset of motion and the rheology of the material, in particular elastic behaviour below the yielding point. Particular attention has been paid to investigating the dynamic response of gel during the bubble growth. Subjecting the bubble to a periodic change in the pressure confirms the irreversibility of the gel deformation and its hysteresis, which are hallmarks of nonlinear viscoelastic behaviour of the gel before yielding. In this context, the periodic expansion and contraction of the bubbles leave residual deformation (stresses) in the gel which facilitates the liberation of bubbles.

Bubble-induced entrainment at viscoplastic–Newtonian interfaces

“…During the last few decades, many theoretical and computational studies have been performed focused at determining the yield surfaces around moving objects in viscoplastic fluids (Tsamopoulos et al 2008;Sikorski, Tabuteau & de Bruyn 2009;Dimakopoulos, Pavlidis & Tsamopoulos 2013;Lopez, Naccache & de Souza Mendes 2018;Chaparian & Frigaard 2021;Pourzahedi et al 2022;Daneshi & Frigaard 2023;Kordalis et al 2023). Theoretical and computational studies amongst these are often based upon a model of ideal (or simple) viscoplastic fluids, as defined in Frigaard (2019).…”

“…Experimentally, deviation from ideal viscoplastic behaviour is always present. Experimental observations find fore-and-aft asymmetries in moving bubbles, even at low Reynolds numbers, characterised by an inverted teardrop shape of the bubble as it rises and a negative wake at the rear of the bubble (Sikorski et al 2009;Mougin, Magnin & Piau 2012;Lopez et al 2018;Zare & Frigaard 2018;Pourzahedi, Zare & Frigaard 2021;Daneshi & Frigaard 2023).…”

“…2008; Sikorski, Tabuteau & de Bruyn 2009; Dimakopoulos, Pavlidis & Tsamopoulos 2013; Lopez, Naccache & de Souza Mendes 2018; Chaparian & Frigaard 2021; Pourzahedi et al. 2022; Daneshi & Frigaard 2023; Kordalis et al. 2023).…”

“…2009; Mougin, Magnin & Piau 2012; Lopez et al. 2018; Zare & Frigaard 2018; Pourzahedi, Zare & Frigaard 2021; Daneshi & Frigaard 2023). These features are attributed to viscoelastic behaviour of the fluid around the bubble (Moschopoulos et al.…”

From yield stress to elastic instabilities: Tuning the extensional behavior of elastoviscoplastic fluids

“…The inherent elasticity of EVP fluids extends beyond their solid state, shaping their flow characteristics, enabling energy storage, and recovery postdeformation ( 8 ). This characteristic plays a crucial role in diverse phenomena, such as the loss of fore–aft symmetry and the formation of negative wakes behind sedimenting particles ( 9 , 10 ), and the inverted teardrop shape of bubbles rising through EVP fluids ( 11 , 12 ). In practical applications, such as 3D printing, the extensional behavior of EVP fluids can enhance process efficiency ( 13–15 ), yet it is often accompanied by challenges like the formation of secondary droplets and elongated capillary tails that compromise precision ( 16 ).…”