The Elasticity of Soap Bubbles Containing Wormlike Micelles

Abstract

Slow-motion imaging of the rupture of soap bubbles generally shows the edges of liquid films retracting at a constant speed (known as the Taylor−Culick velocity). Here we investigate soap bubbles formed from simple solutions of a cationic surfactant (cetyltrimethylammonium bromide -CTAB) and sodium salicylate. The interaction of salicylate ions with CTAB leads to the formation of wormlike micelles (WLM), which yield a viscoelastic behavior to the liquid film of the bubble. We demonstrate that these elastic bubbles collapse at a velocity up to 30 times higher than the Taylor−Culick limit, which has never been surpassed. This is because during the bubble inflation, the entangled WLM chains stretch, storing elastic energy. This extra energy is then released during the rupture of the bubble, yielding an additional driving force for film retraction (besides surface tension). This new mechanism for the bursting of elastic bubbles may have important implications to the breakup of viscoelastic sprays in industrial applications.

Single bubble and drop techniques for characterizing foams and emulsions

“…Notably, Debrégeas et al [187] have shown that during rupture, buckling instabilities can occur on the surface of bubbles in polymer melts. Sabadini et al, [186] on the other hand, have interestingly reported a complete absence of a rim (the tip of the expanding hole where liquid accumulates) in bubbles rupturing in viscoelastic wormlike micellar solutions. The reason for this is currently unknown.…”

“…Firstly, recent studies have revealed the influence of bulk elasticity in the hole opening kinetics of bubbles in a number of systems such as Boger fluids [185], wormlike micelles [186], and polymer melts [187]. In all cases, at short times, bulk elasticity was revealed to increase the hole opening velocity by as much as 10 4 times as compared to a Newtonian fluid of similar viscosity.…”

Ageing and burst of surface bubbles

“…These thickness measurements are consistent with a highly efficient localized Marangoni-driven thinning (T cap < T needle ) or thickening (T cap > T needle ) the cap. It should be noted how such needle localized perturbations affect the measurement of thickness h. Hence, care is needed when interpreting the relationship between the thickness of a film and its rupturing speed when the film is pierced using surface-active perturbations such as heat (Petit, Le Merrer & Biance 2015) or ethanol (Sabadini, Ungarato & Miranda 2014). For h ∼ 0.5-1 µm, the bubbles are thin enough that even less efficient mechanisms such as non-Marangoni-driven intrinsic intrusions (microbubbles or particles) can locally thin the film further for van der Waals forces and thermal fluctuations to be able to act.…”

Bubble impingement in the presence of a solid particle: A computational study

“…In any kind of liquid matrix, bubble walls may also break because of the presence of impurities like solid particles [20,21,22]. Bubble rupture, in turn, can open the way to liquid film retraction, whose extent and velocity depend on the interplay among inertial, surface, viscous, and elastic forces (in case the liquid phase is viscoelastic) [23,24,25,26,27]. The presence of solid objects suspended in the liquid matrix, then, can play a crucial role, since it can anticipate bubble rupture and affect the final morphology of the material [27].…”