Field induced anisotropic cooperativity in a magnetic colloidal glass

Abstract

The translational dynamics of a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. This powerful control parameter finely tunes the anisotropy of the intricate energy landscape in the colloidal glass-former, which is seen here as a new tunable model-system to probe the dynamical heterogeneities at the approach of the glass transition. Both structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

SAXS Analysis of Magnetic Field Influence on Magnetic Nanoparticle Clusters

“…These properties have aroused the interest of researchers in the field of chemistry and physics of condensed matter and in the development of nanotechnologies [4], in biomedical [5] and industrial applications. Recent studies have intensified the local colloidal structure in ferrofluids, and have mainly used the technique of small angle scattering; Fu et al (2016) [6] investigated the self-assembly of supercrystals field-induced colloidal structure of core-shell NPs of core-shell iron oxide dispersed in toluene by small angle neutron scattering (SANS); Rozynek et al (2011) [7] the effect of magnetic field on the structure formation in an oil-based magnetic fluid with various concentrations of magnetite particles by SAXS; Campi et al (2019) [8] analyzed nanoparticles clusters of nickelate perovskite by SµXRD (Scanning X-ray micro-Diffraction); Campi et al (2019) [9] investigated hybrid nanoparticles diffusion and nanoscale aggregation, and observed how fractal dimensional changes leading to a mass surface fractal transition (SAXS); and Wandersman et al (2015) [10] field induced anisotropic cooperativity in a magnetic colloidal glass. We can emphasize the study of the local colloidal structure with the objective of improving in the applications in the field of medicine, with specific use in hyperthermia in the treatment of cancer.…”

Anomalous Dynamics of Magnetic Anisotropic Colloids Studied by XPCS

“…Though the basic principle of XPCS is analogous to that of DLS, the use of X‐rays instead of visible light makes it more suitable to circumvent problems related to multiple scattering and absorption that are often encountered in DLS when opaque systems like magnetic colloids are being investigated. Most of the experimental studies with XPCS involving dynamics of magnetic colloids dealt with spherical particles barring a few that involved the dynamics of anisotropic magnetic particles . Here, it is important to point out that the application of an external magnetic field not only influences the orientation of the particles, but also the overall interparticle interaction potential as it induces or alters an additional magnetic dipolar contribution.…”

Ferrofluids and bio-ferrofluids: looking back and stepping forward

“…Under an external magnetic field, the structure-factor becomes anisotropic. 119,333,334 The presence of such anisotropy (Fig. 17c) shows that there is a preferable positioning of the particles along the field direction around a reference particle, the effect of interaction of the oriented magnetic dipoles.…”

“…Time resolved X-ray photon correlation spectroscopy evidenced highly anisotropic cooperativity on interparticle length scales induced by the applied magnetic field. 119…”