Binary colloidal structures assembled through Ising interactions

• Published in: Nature communications Vol. 3; no. 1; p. 794
• Main Authors: Khalil, Karim S., Sagastegui, Amanda, Li, Yu, Tahir, Mukarram A., Socolar, Joshua E. S., Wiley, Benjamin J., Yellen, Benjamin B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.04.2012; Nature Publishing Group
• Subjects: 639/301/119/997; 639/301/923/966; 639/638/563/982; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms1798

New methods for inducing microscopic particles to assemble into useful macroscopic structures could open pathways for fabricating complex materials that cannot be produced by lithographic methods. Here we demonstrate a colloidal assembly technique that uses two parameters to tune the assembly of over 20 different pre-programmed structures, including kagome, honeycomb and square lattices, as well as various chain and ring configurations. We programme the assembled structures by controlling the relative concentrations and interaction strengths between spherical magnetic and non-magnetic beads, which behave as paramagnetic or diamagnetic dipoles when immersed in a ferrofluid. A comparison of our experimental observations with potential energy calculations suggests that the lowest energy configuration within binary mixtures is determined entirely by the relative dipole strengths and their relative concentrations. The assembly of microscopic particles into macroscopic structures may allow the fabrication of complex materials, but general strategies to provide a wide variety of structures are lacking. Khalil et al . develop a colloidal assembly system, which can be tuned to provide over 20 different pre-programmed structures.