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

Abstract

Understanding the aggregation of magnetic particles is also essential for their use in the fabrication of metamaterials, [8] as magnetic separation agents in, e.g., protein purification protocols, [9] as contrast agents in magnetic resonance imaging, [10] or as cell manipulation operators [11] among others.Floating magnetic particles have also been extensively used in the bottom-up fabrication of different dynamic selfassemblies, which develop order at the same time as dissipate energy. The strong confinement of a system of particles can dramatically influence both the nature of their interactions and the long-range order possible, permitting the existence of new structures and phases both in equilibrium [12,13] and out of equilibrium. [12,14] Besides, the quasi 2D nature of these systems facilitates the experimental analysis of the structure and dynamics. 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

Microrobot collectives with reconfigurable morphologies, behaviors, and functions

“…Other systems, like the one used in this study, use capillary interactions by patterning edge corrugations on micro-disks so that the micro-disk collectives self-organize into square lattices 24 and rotating collectives 35 , 36 . Other microrobotic systems have demonstrated ribbon, chain or vortex formations 25 – 27 , 47 – 49 , locomotion 42 , 50 , and object manipulation 51 , 52 . One study shows impressive locomotion of two microrobotic swarms that can navigate through various mediums and complex environments; however, each swarm demonstrates a single mode, one creates ribbon-like formations while the other creates vortex-like formations 53 .…”

Field-Pulse-Induced Annealing of 2D Colloidal Polycrystals

“…At low frequencies, this time-dependent field forces the formation of elongated structures that vibrate or rotate, synchronously or asynchronously, with the applied field [ 43 ]. If the frequency of the field is higher than 10 Hz, however, an averaged attractive potential promotes the formation of circular assemblies or chains composed of rotating particles, which, in turn, rotate or vibrate in the plane of the field [ 37 , 44 ]. When and are similar, the application of the high-frequency rotating field induces an isotropic effective attractive dipolar potential at the interface plane, , where is the vacuum magnetic permeability and is the induced magnetic moment in the particles, and promotes the formation of two-dimensional colloidal polycrystals.…”

“…The use of magnetic colloids in the study of the annealing of 2D colloidal polycrystals is justified since they allow the induction of interparticle interactions with different characteristics—range, anisotropy and intensity—easily tunable by the action of an externally applied magnetic field of moderate intensity. In the explored configuration, in which the particles are forced to reside in the plane of the interface, the particles have easily tunable attractive and repulsive interactions, isotropic or anisotropic, through modulation of the external magnetic field so they can be assembled or disassembled in a controlled manner [ 4 , 36 , 37 ]. Concretely, the adjustment of the angle between the confining interface and the precessing applied field, which here plays the role of temperature in molecular systems, allows for accelerating or decelerating both the melting and the freezing rates [ 38 , 39 , 40 ].…”

Chain Assembly Kinetics from Magnetic Colloidal Spheres

“…Analogous to molecular subunits within polymers, colloidal particles can also be used as the self-repeating monomeric precursors, linking into 1D colloidal chains. To achieve this, various strategies have been proposed for the fabrication of colloidal chains with distinct architectures, lengths, and compositions including chemical bonding, , electrostatic interactions, ,, hydrogen bonding, directional interaction patches, ,, coordination chemistry, heat, optical traps, UV light, and external fields. ,,− We have recently demonstrated the fabrication of chains that were chemically linked from beads assembled under a 1D magnetic field and have also shown that these colloidal chains can be actuated via different mechanisms upon magnetic field application. , …”