Abstract
<jats:p>Competition between short-range attractive (SA) and long-range repulsive (LR) interactions is predicted to stabilize a variety of structured colloidal mesophases, but kinetic arrest limits experimental access to the fully equilibrated states. Here, we use computer simulations and experiments to study how external fields drive structure formation arising from competitive interactions in quasi-two-dimensional colloidal mixtures of large and small microspheres immersed in a magnetized ferrofluid. Application of a magnetic field normal to the colloidal monolayer induces dynamic, competitive (d- SALR) interactions between colloids that are asymmetric and highly tunable. The equilibrium states stabilized by these interactions, as predicted by Monte Carlo simulations, are dominated by phase-separated, species-enriched solids or cluster fluids. In sharp contrast, Brownian dynamics simulations reveal long-lived, mixed-species clusters with static and dynamic properties that mimic those observed in optical microscopy experiments. Force-weighted graph characteristics and triplet-angular analyses establish how microsphere mixing ratio and magnetic field strength modulate the size distribution and dynamic persistence of the colloidal clusters. These findings highlight new opportunities for using particle size asymmetry in magnetized ferrofluids to design dynamically tunable and structurally complex, out-of-equilibrium colloidal materials.</jats:p>