Dual nature of magnetic nanoparticle dispersions enables control over short-range attraction and long-range repulsion interactions

Abstract

Competition between attractive and repulsive interactions drives the formation of complex phases in colloidal suspensions. A major experimental challenge lies in decoupling independent roles of attractive and repulsive forces in governing the equilibrium morphology and long-range spatial distribution of assemblies. Here, we uncover the ‘dual nature’ of magnetic nanoparticle dispersions, particulate and continuous, enabling control of the short-range attraction and long-range repulsion (SALR) between suspended microparticles. We show that non-magnetic microparticles suspended in an aqueous magnetic nanoparticle dispersion simultaneously experience a short-range depletion attraction due to the particulate nature of the fluid in competition with an in situ tunable long-range magnetic dipolar repulsion attributed to the continuous nature of the fluid. The study presents an experimental platform for achieving in situ control over SALR between colloids leading to the formation of reconfigurable structures of unusual morphologies, which are not obtained using external fields or depletion interactions alone.

Abstract

Competition between attractive and repulsive interactions between colloidal particles drives the formation of complex assemblies. Here, the authors exploit the dual functionality of magnetic nanoparticle dispersions to simultaneously drive attraction and repulsion between suspended non-magnetic microspheres, allowing for precise tuning of the interaction energy landscape of colloidal particles.