Agglomeration and chain formation in ferrofluids: Two-dimensional x-ray scattering

Abstract

We present a comprehensive study of field-induced anisotropy in ferrofluids using two-dimensional smallangle x-ray scattering. On application of a homogeneous magnetic field, magnetite particles form anisotropic clusters with preferred orientation parallel to the field. The orientation of single nonspherical particles contributes little to structural anisotropy, since their effective axis ratio is only about 1.05. We determine the average radius of particles in clusters to be of the order of the mean particle radius in the ferrofluid, i.e., 4-5 nm. Therefore, particles of all sizes contribute to cluster formation. Since the thermal energy exceeds the magnetic dipole-dipole interaction of small particles, thermally stable clusters cannot form without an additional interaction energy. We show that van der Waals interaction yields a significant contribution that cannot be neglected in polydisperse systems.

Self organization in oleic acid-coated CoFe2O4 colloids: a SAXS study

“…The present analysis in terms of an aggregation parameter supports previous studies that indicate that van der Waals interaction yields a significant contribution and cannot be neglected (Kruse et al 2003a). Furthermore, our work showed that the steric interaction, determined by coating molecules arranging and their entropy and mobility, is also relevant.…”

Magnetic and optical response of tuning the magnetocrystalline anisotropy in Fe3O4 nanoparticle ferrofluids by Co doping

“…2 of Ref. [20] was used. We performed measurements using both unpolarized and linearly polarized light having various orientations relative to the applied magnetic field.…”

“…We discuss the field-induced relaxation and optical anisotropic behavior of the two samples within the framework proposed by Kruse et al [20], extended to two-dimensional light scattering. In this framework, the measured intensity of the transmitted light in ferrofluids depends both on scattering from individual nanoparticles and from collections of nanoparticles.…”

“…It has been shown that the magnetic nanoparticles in ferrofluids have dipole-dipole and van der Waal-type interactions, which may lead to chain and cluster formation [19][20][21]. In order to more completely investigate ferrofluid magnetohydrodynamics, it is desirable to control the magnetic properties of nanoparticles independent of their size.…”

Study of low concentrated ionic ferrrofluid stability in magnetic field by ultrasound spectroscopy

“…Steric repulsion prevents particle agglomeration in surfactant-containing MF while coulombic repulsion accounts for the stability in ionic MF [8]. The structure of MF is changed under the influence of magnetic field, magnetic particles form aggregates (clusters) which tend to join into a chain-like clusters of micrometer size [9][10][11][12][13][14]. The field induces changes in the percentage of solid colloidal particles included in aggregates and the packing factor of these particles within the aggregates.…”