Collective Transport of Magnetic Microparticles at a Fluid Interface through Dynamic Self‐Assembled Lattices

Abstract

The transport of confined micron-sized particles plays an important role in a range of phenomena in biology, colloidal science, and solid-state physics. Here, an easily implementable strategy that allows for the collective and monitored transport of magnetic colloidal particles along fluid-fluid interfaces is introduced. Adsorbed microparticles are carried on time-dependent magnetic potentials, generated by dynamic self-assembled lattices of different-sized particles confined onto a parallel plane. In such binary system, the synchronized inversion of the precessing applied field allows for the ballistic and directional transport of the motile components along prescribed directions. The transportation mode can be tuned through the stoichiometry or the strength and orientation of the applied field. The described methodology can be used in the capture and manipulation of drugs or pollutants adsorbed on liquid surfaces, the segregation of colloidal mixtures or the assisted mixture of surface active molecules.

Static and Dynamic Self‐Assembly of Pearl‐Like‐Chains of Magnetic Colloids Confined at Fluid Interfaces

“…[7,37,41] Finally, we have devised a new way for the steering of non-magnetic micron-sized particles along the parallel pearllike-chains of rotating magnetic colloids, all of them adsorbed onto the fluid interface. Unlike previous strategies developed for transporting objects trapped at fluid interfaces, which use interfacial physical effects such as Marangoni effects, [44] gradients in concentration, [45] the self-generation of standing waves, [16c] magnetocapillary effects [46] or the modulation of the potential generated by asymmetrically adsorbed magnetic particles, [17] in this work the passive particles are dragged by the hydrodynamic conveyor belt generated by the rolling species, through a strategy that can be monitored via the application of suitable magnetic manipulation techniques and does not need of direct contact with the cargo. The chain structures created by such actuations demarcate lanes along which adsorbed cargos can be transported.…”

“…[21] As a result of the strong confinement, magnetic particles self-assemble in a set of unique arrangements, determined by the contact angle at the particle's surface, the actuation of the applied field and the anisotropic character of the magnetic interactions. [17,22] Under a constant field normal to the interface, the confined particles interact via a soft centrosymmetric dipole−dipole repulsion, which induces spatial ordering in relatively dense monolayers of monodisperse particles. In crowded conditions, such systems were shown to gradually pass through the three phases predicted by the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory -liquid, hexatic and hexagonal solid-as the ratio between the pair interaction and the kinetic energy of each bead increases, as a result of the progressive increase of the external field.…”

“…In this regard, magnetic colloids adsorbed at liquid-liquid interphases have been proven to be suitable model systems to investigate the formation of static and dynamic arrangements of particles, and promising candidates to engineer novel functional planar structures unfeasible in bulk dipolar systems. [15,16,17] Grzybowski et al studied disparate dynamic structures formed by rotating millimeter-sized magnetic disks, in processes ruled by the equilibrium between…”

Cooperative Self-Assembled Magnetic Micropaddles at Liquid Surfaces

“…The cooperation of these microswimmers becomes essential for more complicated manipulation tasks. Some self-assembled microswimmers and swarms cooperate as partners to enhance interaction forces that they apply on targets during the delivery of objects, − and they could also accomplish parallel cargo transportation to promote efficiency . However, the majority of these partners transport only one object between them or they all deliver their own loads along similar paths.…”

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

“…Rapid advancements in microfabrication favored the elaboration of artificial micro- and nanomotors , capable of moving autonomously and performing various complex tasks. − Such systems are of special interest for biomedical applications, − chemical processes, , environmental remediation, − fighting against pathogenic bacteria, and (bio)­sensing. , Nowadays, a large variety of micro- and nanomotors are elaborated or under research, namely, nanowires, , tubular micromotors, , smart polymers, active patchy colloids, Janus micro- and nanomotors, − porous micromotors, liquid crystalline elastomer particles, Janus micromotors with nanotails, micro- and nanomotors based on inorganic oxides, helical micromotors, and micromotors based on the asymmetry in crystalline phases . Micro- and nanomotor motion is induced by external energy sources (light, ultrasound, and magnetic or electric fields) or via transformation of chemical energy into kinetic energy and is defined by mechanisms such as interfacial tension gradient, electrowetting, self-diffusiophoresis, bubble propulsion, and self-electrophoresis. − …”