Generation of Amphiphilic Janus Bubbles and Their Behavior at an Air–Water Interface

Abstract

This paper presents the generation of amphiphilic Janus bubbles and their behavior at an air–water interface. Janus bubbles are generated by selectively depositing gold onto one side of dried nanoparticle‐shelled bubbles. To generate nanoparticle‐shelled bubbles that can withstand drying without significant changes in their structure, it is critical to control the ratio of bubble radius to shell thickness using a microfluidic technique. It is observed that the behavior of Janus bubbles at an air–water interface is very different from that of unmodified nanoparticle‐shelled bubbles. Interfacial assembly of amphiphilic Janus bubbles shows that they interact with one another via long‐ranged attractions. The origin of this long‐ranged attraction is quadrupolar capillary interactions due to the undulation of the three‐phase contact line around the Janus boundary. The interparticle forces between interface‐trapped Janus bubbles are determined using a particle tracking method. The shape of the deformed air–water interface around Janus bubbles is directly observed as well as the orientation of Janus bubbles using a gel‐trapping technique. These observations verify that the air–water interface is pinned around the boundary between the two hemispheres and that the chemical heterogeneity of this boundary leads to irregular contact line around Janus bubbles.

One-step microfluidic production of gas-in-water-in-oil multi-cores double emulsions

“…In the steady flow pattern, the average pressure and flow rate can be controlled. 24 . The images of the two flow patterns can be seen in Fig.…”

“…Upon evaporation of the organic solvent, the nanoparticles in the oil layer form a stiff shell at the air-water interface, which enhances the stability of the microbubbles against dissolution and coarsening. Teresa et al 24 also used the same device to prepare gas-in-oil-in-water double emulsions. Stride et al 25 reported a one-step approach to produce hollow microspheres with single holes in the shells by coaxial electrohydrodynamic atomization(CEHDA).…”

Formation of Polymeric Hollow Microcapsules and Microlenses Using Gas-in-Organic-in-Water Droplets

“…However, it was essential to match the generation rate and pitch of the droplets and the method often produced relatively thick shells. In contrast, Luo et al [28][29][30] and Lee et al [31][32][33] reported droplet formation methods using three-dimensional glass capillaries. They used a separated serial or simultaneous droplet generation structure to form core and shell layers.…”

“…Highly uniform microcapsules have been formed in miniaturized devices, and the functionality of these microcapsules has expanded as a result of new developments in microcapsule synthesis [22][23][24]. Formation of hollow microcapsules by direct injection of a gas into the capsule core is of particular interest [25][26][27][28][29][30][31][32][33][34]. Since the inner cavity and shell layer are formed directly in this technique, the number of materials available for capsule synthesis was significantly increased compared with single emulsion techniques using self-assembly or interfacial polymerization of the shell layer [35][36][37].…”

Thermodynamically Stable Emulsions Using Janus Dumbbells as Colloid Surfactants

“…We also assume that the Janus boundary does not cause undulation in the fluid interface, thus does not induce lateral capillary attractions between Janus dumbbells. [45][46][47][48][49] Results and Discussion…”