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

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2021-06, Vol.17 (25), p.e2101188-n/a
• Main Authors: Martínez‐Pedrero, Fernando, González‐Banciella, Andrés, Camino, Alba, Mateos‐Maroto, Ana, Ortega, Francisco, Rubio, Ramón G., Pagonabarraga, Ignacio, Calero, Carles
• Format: Article
• Language: English
• Subjects: 2D confined systems; Acceleration; Actuation; Assembly; Chains; Chemical reactions; colloidal transport; Colloids; Computational fluid dynamics; Confined spaces; dynamic self‐assembly; Fluid flow; fluid interface; Gravity conveyors; Hydrodynamics; Interfaces; Nanotechnology; superparamagnetic particles; Viscous flow
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202101188

Magnetic colloids adsorbed at a fluid interface are unique model systems to understand self‐assembly in confined environments, both in equilibrium and out of equilibrium, with important potential applications. In this work the pearl‐chain‐like self‐assembled structures of superparamagnetic colloids confined to a fluid–fluid interface under static and time‐dependent actuations are investigated. On the one hand, it is found that the structures generated by static fields transform as the tilt angle of the field with the interface is increased, from 2D crystals to separated pearl‐chains in a process that occurs through a controllable and reversible zip‐like thermally activated mechanism. On the other hand, the actuation with precessing fields about the axis perpendicular to the interface induces dynamic self‐assembled structures with no counterpart in non‐confined systems, generated by the interplay of averaged magnetic interactions, interfacial forces, and hydrodynamics. Finally, how these dynamic structures can be used as remotely activated roller conveyors, able to transport passive colloidal cargos at fluid interfaces and generate parallel viscous flows is shown. The latter can be used in the mixture of adsorbed molecules and the acceleration of surface‐chemical reactions, overcoming diffusion limitations. The study of static and dynamic self‐assembly in driven and confined systems has displayed a crucial role in the development of new swimming and micromanipulation techniques. This work shows and explains the emergence of parallel buoy lane markers composing by rotating spheres, which can be used to mix and transport colloids and molecules adsorbed at a fluid interface.