Magnetic field-induced self-assembly of iron oxide nanocubes.

Gurvinder Singh,Artem Baskin,Petr Král,Henry Chan,Davide Peddis,Gregory Leitus,T Udayabhaskararao,Rafal Klajn,Elijah Gelman

doi:10.1039/c4fd00265b

Abstract

Self-assembly of inorganic nanoparticles has been studied extensively for particles having different sizes and compositions. However, relatively little attention has been devoted to how the shape and surface chemistry of magnetic nanoparticles affects their self-assembly properties. Here, we undertook a combined experiment-theory study aimed at better understanding of the self-assembly of cubic magnetite (Fe3O4) particles. We demonstrated that, depending on the experimental parameters, such as the direction of the magnetic field and nanoparticle density, a variety of superstructures can be obtained, including one-dimensional filaments and helices, as well as C-shaped assemblies described here for the first time. Furthermore, we functionalized the surfaces of the magnetic nanocubes with light-sensitive ligands. Using these modified nanoparticles, we were able to achieve orthogonal control of self-assembly using a magnetic field and light.

Highlights

Inorganic nanoparticles (NPs) can be self-assembled[1,2] into nanostructured materials with emergent properties that differ from those of isolated NPs, or of the corresponding bulk phases.[3,4,5,6,7,8,9,10] The characteristics of such self-assembled materials are determined by nanoscale interactions between NPs arranged in a speci c fashion, giving rise to, for example, unique electrical,[3] optical,[4] or magnetic[5] properties
Magnetic dipole moments of these nanoparticles are randomized unless an external magnetic eld is applied, in which case the dipoles tend to align themselves along the lines of the eld, so that magnetic dipole–dipole interactions between the NCs can be controlled
We found that the nature of these assemblies strongly depends on the concentration of the NC building blocks: whereas simple one-dimensional laments were obtained at low NC densities and laments featuring a “diamond-type” arrangement of the NCs were observed at intermediate densities, high NC loadings resulted in the formation of helical assemblies (Fig. 2).[15]

Summary

Introduction

Inorganic nanoparticles (NPs) can be self-assembled[1,2] into nanostructured materials with emergent properties that differ from those of isolated NPs, or of the corresponding bulk phases.[3,4,5,6,7,8,9,10] The characteristics of such self-assembled materials are determined by nanoscale interactions between NPs arranged in a speci c fashion, giving rise to, for example, unique electrical,[3] optical,[4] or magnetic[5] properties. Magnetic dipole–dipole interactions have been studied extensively as the driving force for NP self-assembly,[11,12] with the advantage that aDepartment of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel. E-mail: rafal.klajn@ weizmann.ac.il bDepartment of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway cDepartment of Chemistry, University of Illinois, Chicago, IL 60607, USA dInstitute of Structure of Matter, National Research Council (CNR), 00016 Monterotondo Scalo, Roma, Italy eChemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel fDepartment of Physics, University of Illinois, Chicago, IL 60607, USA. The vast majority of the previous studies have focused on NPs free of any functional ligands that could actively in uence the self-assembly process

Methods

Results

Conclusion