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

Abstract

Micromotors are fascinating objects that are able to move autonomously and perform various complex tasks related to drug delivery, chemical processes, and environmental remediation. Among the types of micromotors, droplet-based micromotors are characterized by a wide range of functional properties related to the capability of encapsulation and deformation and the possibility of using them as microreactors. Relevant problems of micromotor utilization in the chemical processes include intensification of mixing and locomotion of passive objects. In this paper, the technique for preparation of superfast active droplets, which can be used as micromotors for effective locomotion of passive droplets in the oil-in-water emulsion, is demonstrated. The possibility of passive droplet locomotion in the emulsion is determined by a relation between the diameters of active and passive droplets. If the diameter of active droplets is larger than the diameter of passive droplets, the agglomerates form spontaneously in the emulsion and move in a straight line. In the case of the opposite relation between diameters, the agglomerates consisting of active and passive droplets rotate intensively. This makes it impossible to move the passive droplets to a given distance. Such micromotors can achieve unprecedentedly high velocities of motion and can be used to intensify mixing on the microscales.

Motion of a self-propelled particle with rotational inertia

“…2a. Such motion was experimentally observed for active emulsion droplets in a bulk liquid (V 0 /V T c 1, o/n fr { 1) 35,36 and vibrobots (V 0 /V T B 10, o/n fr o 0.5) 67 with overdamped random rotation, as well as for synthetic surfers (o/n fr B 40) and crawlers (o/n fr B 5) with underdamped rotation. 58 An increase in the effective kinetic temperature was also realized by a rapid rotation of the driving force acting on a nanoparticle (o/n fr t 10 3 ) optically trapped in a vacuum chamber.…”

“…Artificial microswimmers can be driven, for instance, by diffusiophoresis, 26,27 thermophoresis, 28 electrophoresis (electroosmosis), [29][30][31] bubble thrust 32,33 or interfacial tension gradient. [34][35][36] The dynamics of a solitary microswimmer in a normal liquid is significantly overdamped and represents a combination of translational Brownian motion and propulsive motion coupled with random rotation (reorientation). For example, the runand-tumble particle (RTP) 7,8,11,16,18 is proposed as a model for a swimming bacterium that reorients itself due to sudden turns, and minimal models of the active Brownian particle (ABP) 4,6,11,15,[17][18][19]23 and active Ornstein-Uhlenbeck particle (AOUP) [19][20][21][37][38][39][40][41][42][43][44][45] are often used to describe the translational motion of an artificial microswimmer with slow angular diffusion caused by thermal fluctuations.…”

“…Artificial microswimmers can be driven, for instance, by diffusiophoresis, 26,27 thermophoresis, 28 electrophoresis (electroosmosis), 29–31 bubble thrust 32,33 or interfacial tension gradient. 34–36…”

Magnetic Manganese‐Based Micromotors MnFe2O4@Fe3O4/graphite and Mn2O3@Fe2O3@Fe3O4/graphite for Organic Pollutant Degradation

“…Micro/nanomotors are devices that are able to convert the environmental energy into the kinetic energy of its motion. [7][8][9][10] A great variety of micro/nanomotors, which differ in both their structure and composition as well as the motion principles, has been developed. [11][12][13][14][15] The motion of micro/nanomotors can be caused by the action of light, [16] magnetic [17] and electric fields, [18] and chemical reactions.…”

Magnetic Nanomotors in Emulsions for Locomotion of Microdroplets

“…The world of micro-/nanomotors is extremely diverse. − The wide research interest in such systems is due to a variety of applied problems, which can be solved with their use in fields such as medicine, − ecology, − elaboration of sensors, − degradation of antibiotics, and antibiotic therapy. , Nowadays, many micro-/nanomotors are under study: Janus micro- and nanomotors, − helical micromotors, tubular micromotors, self-propelled droplets, − biohybrid robotics, and micromotors on the base of metal oxides. − The motion of micro-/nanomotors can be due to different factors such as light, − chemical reactions, − and effects of acoustic, electric, or magnetic fields. − In the case of using a magnetic field, micro-/nanomotors can convert the energy of magnetic field into mechanical energy. Significant research interest to this method of micro-/nanomotor locomotion is because a low-intensity magnetic field is harmless for living organisms.…”