Driving self-assembly and emergent dynamics in colloidal suspensions by time-dependent magnetic fields

Abstract

In this review we discuss recent research on driving self-assembly of magnetic particle suspensions subjected to alternating magnetic fields. The variety of structures and effects that can be induced in such systems is remarkably broad due to the large number of variables involved. The alternating field can be uniaxial, biaxial or triaxial, the particles can be spherical or anisometric, and the suspension can be dispersed throughout a volume or confined to a soft interface. In the simplest case the field drives the static or quasistatic assembly of unusual particle structures, such as sheets, networks and open-cell foams. More complex, emergent collective behaviors evolve in systems that can follow the time-dependent field vector. In these cases energy is continuously injected into the system and striking flow patterns and structures can arise. In fluid volumes these include the formation of advection and vortex lattices. At air-liquid and liquid-liquid interfaces striking dynamic particle assemblies emerge due to the particle-mediated coupling of the applied field to surface excitations. These out-of-equilibrium interface assemblies exhibit a number of remarkable phenomena, including self-propulsion and surface mixing. In addition to discussing various methods of driven self-assembly in magnetic suspensions, some of the remarkable properties of these novel materials are described.

Dynamics of dissipative self-assembly of particles interacting through oscillatory forces

“…15,21,30 On the other hand, when the coupling between the system and the energy source is periodically modulated, some external or internal variable must oscillate in time, such as the strength of the interactions between particles 17,20,[31][32][33] or the magnitude and direction of an external field. 5,7,16,[34][35][36][37] In these cases, the system evolves in time toward a non-equilibrium steady-state (NESS) that is oscillatory in nature: the properties of the system in the NESS are equivalent at time t and at time t+τ (where τ is the oscillation period). Dissipative systems may have more than one NESS, 38 so an important and open question is how to control the evolution of these systems toward a specific NESS.…”

Rotating magnetic field-controlled fabrication of magnetic hydrogel with spatially disk-like microstructures

“…Fortunately, the magnetic nanoparticles have a significant advantage of remote manipulation with magnetic field so that the magnetic field-directed assembly of magnetic nanoparticles can be employed to form the ordered structures effectively [13][14][15]. For instance, the modulated magnetostatic magnetic field can direct the long-ranged order of magnetic nanoparticles in macroscopic dimension [16][17][18]. Furthermore, the common biomaterials have demonstrated exceptional magnetocontrollable performance by integration with the magnetic nanoparticles [19][20][21].…”

Transport and selective chaining of bidisperse particles in a travelling wave potential

“…In contrast to optical or electric field micromanipulation, magnetic fields have the advantages that they neither alter the fluid medium nor affect biological systems, although their use is limited to polarizable particles [9,10]. Magnetophoresis, i.e.…”