Two-Stage Assembly of Mesocrystal Fibers with Tunable Diameters in Weak Magnetic Fields

Abstract

Controlling the morphology and crystallographic coherence of assemblies of magnetic nanoparticles is a promising route to functional materials. Time-resolved small-angle X-ray scattering (SAXS) was combined with microscopy and scaling analysis to probe and analyze evaporation-induced assembly in levitating drops and thin films of superparamagnetic iron oxide nanocubes in weak magnetic fields. We show that assembly of micrometer-sized mesocrystals with a cubic shape preceded the formation of fibers with a high degree of crystallographic coherence and tunable diameters. The second-stage assembly of aligned cuboidal mesocrystals into fibers was driven by the magnetic field, but the first-stage assembly of the oleate-capped nanocubes was unaffected by weak magnetic fields. The transition from 3D growth of the primary mesocrystals to the second stage 1D assembly of the elongated fibers was related to the size and field dependence of isotropic van der Waals and directional dipolar interactions between the interacting mesocrystals.

Recent Notable Approaches to Study Self‐Assembly of Nanoparticles with X‐Ray Scattering and Electron Microscopy

“…In combination with a magnetic field, mesocrystalline fibers built from magnetite nanocubes have been achieved. [ 277 ] Before the fibers grew, driven by the magnetic field, micrometer‐sized mesocrystals with a cubic shape were formed. The transition from the 3D to 1D growth could be connected to the size and field dependence of interactions between the interacting mesocrystals.…”

Using small-angle scattering to guide functional magnetic nanoparticle design

“…The particles cluster in intermediate, dense, but disordered precursors that rapidly transform into large mesocrystals. 194,274 Given the well-progressed application of GISAXS to the structural characterization of MNP assemblies, the next important step will be applying grazing-incidence scattering techniques to the understanding of the magnetic morphology in nanoparticle arrangements. Schlage et al 275 combined the structural analysis of in situ grown magnetic antidot arrays using GISAXS with magnetic characterization using nuclear resonance X-ray scattering, revealing the magnetization of the growing iron nanostructure and the impact of an iron oxide capping layer.…”

Controlling the rotation modes of hematite nanospindles by dynamic magnetic fields

“…Field-driven actuation on magnetic particles builds the foundation of various intriguing applications, including self-propelling particles in active matter, 1,2 mixers in microfluidics, 3 and viscosity probes in nanorheology, 4 but also aspects based on structure formation, such as field-induced self-organization [5][6][7] and smart fluids. 8,9 Biological microorganisms such as magnetotactic bacteria are inspiring model systems for magnetic microswimmers 10 operating at low Reynolds numbers, but also large enough so that their movement and dynamics can be tracked by optical techniques.…”