Self-assembly of magnetic colloids under unsteady fields

Abstract

The use of magnetic fields offers an external, versatile way of controlling self-assembly of colloids. This review provides an exhaustive overview of unsteady fields that can vary in one, two, or three dimensions of space, as a powerful tool to direct the self-assembly of magnetic colloids into structures with tunable properties. Unlike steady fields, unsteady (nonstationary) fields can overcome the limitations of classical dipolar interactions, leading to a much wider range of structures, ranging from dense crystalline aggregates to 3D spanning networks, or dynamic clusters. The ability to precisely control the amplitude, frequency, and field direction allows for fine-tuning the interplay of interparticle forces, resulting in controllable assembly pathways. This review analyzes how different types of unsteady fields influence the morphology and dynamics of the self-assembled structures. Key parameters, such as the Mason number, are discussed to characterize the governing driving forces, and potential applications are highlighted.