In-situ investigation of temperature induced agglomeration in non-polar magnetic nanoparticle dispersions by small angle X-ray scattering

TL;DR

This study uses in-situ small angle X-ray scattering to analyze how temperature-induced agglomeration occurs in non-polar magnetic nanoparticle dispersions, revealing size-dependent structural differences.

Contribution

It provides new insights into the size-dependent structural evolution of magnetic nanoparticle agglomerates during cooling, highlighting the roles of magnetic and van der Waals interactions.

Findings

Small and large nanoparticles form similar local packings.

Small particles create compact superstructures; large particles form chain-like agglomerates.

Magnetic dipole interactions influence larger particles, while van der Waals forces dominate smaller ones.

Abstract

Non-polar magnetic nanoparticles agglomerate upon cooling. This process is followed by in-situ small angle X-ray scattering to assess structural properties of the emerging agglomerates. On the length scale of a few particle diameters, no differences are found between the agglomerates of small (d = 12nm) and large (d = 22nm) nanoparticles. Hard-sphere like random packing with a local packing fraction of $\eta$ = 0.4 is seen. On larger length scales, small particle form compact superstructures, while large particles arrange into agglomerates that resemble chain-like structure in SAXS. This can be explained by directed magnetic dipole interactions that dominate larger particles, while isotropic van der Waals interaction governs the agglomeration of smaller particles.