Crystallization of Active Emulsion

Abstract

Active matter contains self-propelled units able to convert stored or ambient free energy into motion. Such systems demonstrate amazing features related to the phenomenon of self-organization and phase transitions and can be used for the development of artificial materials and machines that operate away from equilibrium. Significant advances in the fabrication of active matter were achieved when studying low-density gas and small crystallites. However, the technique of preparation of active matter, where one can observe the formation of stable crystals, is extremely challenging. Here, we describe the novel method to obtain a stable 2D crystal in the active octane-in-water emulsion during the process of heterogeneous crystallization. Active motion is driven by the Marangoni flow emerging at the interface of the droplet. It is established that the crystal volume increases linearly in time in the process of crystallization. Moreover, the dependence of the crystal growth rate on the average velocity of droplets motion in the emulsion has a maximum. The kinetics of crystal growth is defined by a competition between the processes of attachment and detachment of droplets from the crystal surface. Crystallization proceeds via condensation of droplets from the gas phase through the formation of liquid as an intermediate phase, which covers the crystal surface with a thin layer. Inside the liquid layer the bond-orientational order of droplets decreases from the crystal surface toward the gas phase. We anticipate our study to be a starting point for the development of new materials and technologies on the basis of nonequilibrium droplet systems.

Self-Propelled Motion of an Oil Droplet Containing a Phospholipid and its Stability in Collectivity

“…The observed polygonal morphology is similar to the cell morphologies of confluent cells, such as epithelial cells. In most previous studies that examined the collective motion of self-collective droplets, each droplet had a relatively small specific surface area, thus maintaining a small contact area and a spherical shape [34,57]. Therefore, our results are superior to those of previous studies because the droplets could stably adopt a characteristic polygonal shape.…”

“…This oil droplet shows selfpropelled motion driven by Marangoni convection on a glass substrate due to symmetry breaking of interfacial tension owing to the competition between the adsorption of TSA + onto the glass surface and its uptake by the droplet. Although other selfpropelled oil droplets have been reported, some of them move at the air-water interface [34]. In contrast, self-propelled oil droplets developed in this study can move on a glass substrate in a manner similar to the two-dimensional movement of cells on the extracellular matrix.…”

Oscillating Motion of Oil Droplets in the Emulsion Near the Air–Water Interface

“…The dynamics of the ensemble of active objects shows a variety of collective behaviors reminiscent of living organisms. Such systems demonstrate new types of materials organization: self-organized vortices, active turbulence, clusters, crystallization, and vitrification. ,− Active particles can move either in the bulk or near the fluid–fluid interfaces. − In the latter case, the dynamics of active objects is characterized by a set of features related to dimensionality, curvature, and symmetry.…”

Superfast Active Droplets as Micromotors for Locomotion of Passive Droplets and Intensification of Mixing

“…While there is a relatively good understanding of the motion of carrier–cargo systems for solid particles, the same questions for systems of droplets are still unresolved. One of the open questions in the field of soft micromotors is related to the problem of the preparation of the emulsions ,− where the active droplets could effectively transport the passive droplets to the given distance.…”