Assembly of jammed colloidal shells onto micron-sized bubbles by ultrasound

Abstract

Stabilization of gas bubbles in water by applying solid particles is a promising technique to ensure long-term stability of the dispersion against coarsening. However, the production of large quantities of particle stabilized bubbles is challenging. The delivery of particles to the interface must occur rapidly compared to the typical time scale of coarsening during production. Furthermore, the production route must be able to overcome the energy barriers for interfacial adsorption of particles. Here we demonstrate that ultrasound can be applied to agitate a colloidal dispersion and supply sufficient energy to ensure particle adsorption onto the air-water interface. With this technique we are able to produce micron-sized bubbles, solely stabilized by particles. The interface of these bubbles is characterized by a colloidal shell, a monolayer of particles which adopt a hexagonal packing. The particles are anchored to the interface owing to partial wetting and experience lateral compression due to bubble shrinkage. The combination of both effects stops coarsening once the interface is jammed with particles. As a result, stable bubbles are formed. Individual particles can desorb from the interface upon surfactant addition, though. The latter fact confirms that the particle shell is not covalently linked due to thermal sintering, but is solely held together by capillary interaction. In summary, we show that our ultrasound approach allows for the straightforward creation of micron-sized particle stabilized bubbles with high stability towards coarsening.

Harnessing the advantages of hard and soft colloids by the use of core–shell particles as interfacial stabilizers

“…We also observed that initially spherical emulsion droplets attain pronounced non-spherical shapes (Fig. 6b), a property which is known for bubbles 15 and emulsion droplets 36 stabilized by hard particles. Thus, core-shell particles at the oil-water interface seem to Fig.…”

“…We would like to note that electrolyte addition, a well-known way to promote interfacial adsorption of particles, 15 did not seem to help interfacial adsorption of hard particles. We ascertained that for electrolyte concentrations up to 500 mM sodium chloride the very long timescales for surface pressure development by hard particles remain unchanged (data not shown).…”

“…1a. The value t theoretical * is calculated according to eqn (3) with the area number densities G* and the diffusion coefficients D and fixed volume number density c N = 9.25 Â 10 15 1.09 Â 10 11 5.77 Â 10 À13 410 000 187 Core 1.18 Â 10 11 5.96 Â 10 À13 -213 Fig. 2 Microscopy picture of the air-water interface (a) and decane-water interface (b) after interfacial adsorption of core-shell particles CS530.…”

“…14 Promoting particle adsorption thus requires high energy input processing methods such as turbulent mixing or sonication. 15 In the context of applications, it is not always possible to modify the sign of the particle charge or use high energy processing methods. Therefore, an alternative should be welcome.…”

Structure–property relationships of cell clusters in biotissues: 2D analysis

“…Soft stacking system which is composed by cells [1], particles [2] as well as other soft units [3][4][5] often presents particular arrangement. Comparing the soft stacking system with the atom stacking system in solid state physics, the former has more complex structures.…”