Buckling of a colloid-armored bubble (original) (raw)
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Tailoring and understanding the mechanical properties of nanoparticle-shelled bubbles
ACS applied materials & interfaces, 2014
One common approach to generate lightweight materials with high specific strength and stiffness is the incorporation of stiff hollow microparticles (also known as bubbles or microballoons) into a polymeric matrix. The mechanical properties of these composites, also known as syntactic foams, greatly depend on those of the hollow microparticles. It is critical to precisely control the properties of these bubbles to fabricate lightweight materials that are suitable for specific applications. In this paper, we present a method to tailor the mechanical properties and response of highly monodisperse nanoparticle-shelled bubbles using thermal treatment. We characterize the mechanical properties of individual as-assembled bubbles as well as those of thermally treated ones using nanoindentation and quantitative in situ compression tests. As-assembled bubbles display inelastic response, whereas thermally treated bubbles behave elastically. We also show that the stiffness and strength of bubbl...
Microbubbles: Stabilization by monolayers of adsorbed particles
Journal of Geophysical Research, 1987
Stable microbubbles are a ubiquitous feature of natural waters, acting az sites for mechanical and acoustical cavitation and nudeii for bubble growth at low gaz super-saturations. Stable microbubble populations that have been determined acoustically in the pazt are not well explained by existing models of bubble stabilization, i.e., stabilization in particle crevices or stabilization by molecular monolayers. Bazed upon the observation that bubbles rising in sea water rapidly become coated with particles, a model is developed in which bubbles are stabilized mechanically by monolayers of adsorbed nonpolar particles. Long-term bubble stability is demonstrated in laboratory experiments. Predictions bazed on the experiments and the model are, in order of magnitude, consistent with observation. 14,641 149-156, 1986. Yount, D.E., and C.M. Yeung, Bubble formation in supersaturated gelatin:
Langmuir, 2003
By using a classical photo camera and a high-speed video camera, snapshots and time sequences of the dynamics of champagne bubbles collapsing close to each other in a bubble raft composed of quite monodisperse millimetric bubbles were made, thus completing two recent works (Liger-Belair et al. in C. R. Acad. Sci. Paris Série 4 2001, 2, 775-780 and Liger-Belair in Ann. Phys. Fr. 2002, 27 (4), 1-106). Bubble caps of bubbles adjacent to a collapsing one were found to be strikingly stretched toward the lowest part of the cavity left by the central bursting bubble. Orders of magnitude of shear stresses developed in the adjacent deformed bubble caps were indirectly estimated. Our results strongly suggest, in the thin film of adjacent bubble caps, stresses higher than those observed around a single millimetric collapsing bubble. High-speed time sequences also proved that bubble caps in touch with collapsing bubbles were never found to rupture, thus causing in turn a chain reaction. As in the case of single collapsing cavities, it was also observed that a tiny daughter bubble, approximately 10 times smaller than the initial central bursting bubble, was entrapped during the collapsing process of the central cavity.
Stability analysis of an encapsulated microbubble against gas diffusion
Journal of Colloid and Interface Science, 2010
Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein-Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although, bubbles, containing gases other than air is considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided.
Stabilization of liquid foams through the synergistic action of particles and an immiscible liquid
Angewandte Chemie (International ed. in English), 2014
Liquid foams are familiar from beer, frothed milk, or bubble baths; foams in general also play important roles in oil recovery, lightweight packaging, and insulation. Here a new class of foams is reported, obtained by frothing a suspension of colloidal particles in the presence of a small amount of an immiscible secondary liquid. A unique aspect of these foams, termed capillary foams, is the particle-mediated spreading of the minority liquid around the gas bubbles. The resulting mixed particle/liquid coating can stabilize bubbles against coalescence even when the particles alone cannot. The coated bubbles are further immobilized by entrapment in a network of excess particles connected by bridges of the minority liquid. Capillary foams were prepared with a diverse set of particle/liquid combinations to demonstrate the generality of the phenomenon. The observed foam stability correlates with the particle affinity for the liquid interface formed by spreading the minority liquid at the ...
Langmuir, 2005
A novel design of apparatus is described that allows observation of the coalescence stability of bubbles at a planar interface when the planar interface and the bubble surface both expand. Bubbles are introduced beneath the planar air-water interface contained within a square barrier made of perfluorocarbon rubber. The bubbles are then expanded by reducing the air pressure above the interface, while at the same time the rubber barrier is mechanically expanded, maintaining its square shape, to give the same rate and extent of expansion of the planar interface. The area can typically be increased by a factor of three over time scales as short as 0.2 s. This arrangement has been designed to mimic the behavior of aerated products when they exit from a pressurized aeration unit or product dispenser. Compared to results obtained via a previous technique, where it was only possible to expand the bubbles but not the planar interface, the bubbles are less stable. The apparatus has been used to compare the stabilizing effects of ovalbumin,-lactoglobulin, whey protein isolate, and sodium caseinate, in a model aqueous food system thickened with 40% invert sugar. Stability improved with increasing concentration of all the proteins and with a decrease in expansion rate, but considerable instability remained even at protein concentrations as high as 4 to 6 wt % and also at very low expansion rates, though the systems were stable in the absence of expansion. However, the stability was greatly improved by the replacement of the above proteins by the hydrocolloids gelatine or polypropylene glycol alginate. Detailed analysis revealed that the coalescence of individual bubbles in clusters of bubbles were not strongly correlated in distance or time, but larger bubbles and bubbles toward the outside of a cluster were found to be, on average, less stable than smaller bubbles and bubbles located more toward the interior of a cluster. The different degrees of stability are discussed in terms of local deformation, fracture behavior, and time-dependent composition of the adsorbed layers.
Effects of encapsulation elasticity on the stability of an encapsulated microbubble
Journal of Colloid and Interface Science, 2009
A model for gas transport from an encapsulated microbubble into the surrounding medium is developed and investigated incorporating the effects of encapsulation elasticity. Encapsulation elasticity stabilizes microbubbles against dissolution and explains the long shelf life of microbubble contrast agent. We consider air bubbles as well as bubbles containing perfluorocarbon gas. Analytical conditions between saturation level, surface tension and interfacial dilatational elasticity are determined for attaining non-zero equilibrium radius for these microbubbles. Numerical solution of the equation verifies the stability of the equilibrium radii. In an undersaturated medium all encapsulated bubbles dissolve. In a saturated medium, an encapsulated bubble is found to achieve a long-time stable radius when interfacial dilatational elasticity is larger than equilibrium surface tension. For bubbles with interfacial dilatational elasticity smaller than the equilibrium surface tension, stable bubble of non-zero radius can be achieved only when the saturation level is greater than a critical value. Even if they initially contain a gas other than air, bubbles that reach a stable radius finally become air bubbles. The model is applied to an octafluoropropane filled lipid-coated 2.5 lm bubble, which displayed a transient swelling due to air intake before reaching an equilibrium size. Effects of elasticity, shell permeability, initial mole fraction, initial radius and saturation level are investigated and discussed. Shell permeability and mole fraction do not affect the final equilibrium radius of the microbubble but affect the time scale and the transient dynamics. Similarly, the ratio of equilibrium radius to initial radius remains unaffected by the variation in initial radius.
Current Opinion in Colloid & Interface Science, 2020
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A model for large amplitude oscillations of coated bubbles accounting for buckling and rupture
The Journal of the Acoustical Society of America, 2005
We present a model applicable to ultrasound contrast agent bubbles that takes into account the physical properties of a lipid monolayer coating on a gas microbubble. Three parameters describe the properties of the shell: a buckling radius, the compressibility of the shell, and a break-up shell tension. The model presents an original non-linear behavior at large amplitude oscillations, termed compression-only, induced by the buckling of the lipid monolayer. This prediction is validated by experimental recordings with the high-speed camera Brandaris 128, operated at several millions of frames per second. The effect of aging, or the resultant of repeated acoustic pressure pulses on bubbles, is predicted by the model. It corrects a flaw in the shell elasticity term previously used in the dynamical equation for coated bubbles. The break-up is modeled by a critical shell tension above which gas is directly exposed to water.