TY - JOUR

T1 - Anisotropic dynamics of magnetic colloidal cubes studied by X-ray photon correlation spectroscopy

AU - Pal, Antara

AU - Kamal, Md Arif

AU - Zinn, Thomas

AU - Dhont, Jan K.G.

AU - Schurtenberger, Peter

PY - 2021

Y1 - 2021

N2 - Herein we present our results on the investigation of the influence of external magnetic fields on the anisotropic collective dynamics of core/shell colloidal cubes having a hematite core and silica shell. Owing to the hematite cores, these micrometer-sized particles possess permanent dipole moments, which are at an angle with respect to the long diagonal of the cubes. As a result, they self-assemble into chains, which subsequently sediment to form higher-order structures. Using multispeckle ultrasmall-angle X-ray photon correlation spectroscopy, the anisotropic dynamics within these structures at the nearest-neighbor length scale was probed. The relaxation of the intermediate scattering function follows a compressed exponential behavior along all the different directions with respect to the external field-parallel, perpendicular, and at an angle ≈45a-indicating hyperdiffusive behavior. We believe that the inhomogeneous distribution of stress points originating from the interplay of external field-induced (both gravitational and magnetic) alignment of the chains are responsible for the anomalous dynamics. The effective diffusion coefficients along and at ≈45a angle exhibit mild de Gennes narrowing, which is not very common for hyperdiffusive dynamics. We rationalize our observations by considering a superposition of diffusive and stress-induced ballistic processes and argue that depending on the azimuthal direction the relative contribution from these two processes changes.

AB - Herein we present our results on the investigation of the influence of external magnetic fields on the anisotropic collective dynamics of core/shell colloidal cubes having a hematite core and silica shell. Owing to the hematite cores, these micrometer-sized particles possess permanent dipole moments, which are at an angle with respect to the long diagonal of the cubes. As a result, they self-assemble into chains, which subsequently sediment to form higher-order structures. Using multispeckle ultrasmall-angle X-ray photon correlation spectroscopy, the anisotropic dynamics within these structures at the nearest-neighbor length scale was probed. The relaxation of the intermediate scattering function follows a compressed exponential behavior along all the different directions with respect to the external field-parallel, perpendicular, and at an angle ≈45a-indicating hyperdiffusive behavior. We believe that the inhomogeneous distribution of stress points originating from the interplay of external field-induced (both gravitational and magnetic) alignment of the chains are responsible for the anomalous dynamics. The effective diffusion coefficients along and at ≈45a angle exhibit mild de Gennes narrowing, which is not very common for hyperdiffusive dynamics. We rationalize our observations by considering a superposition of diffusive and stress-induced ballistic processes and argue that depending on the azimuthal direction the relative contribution from these two processes changes.

U2 - 10.1103/PhysRevMaterials.5.035603

DO - 10.1103/PhysRevMaterials.5.035603

M3 - Article

AN - SCOPUS:85104334912

SN - 2475-9953

VL - 5

JO - Physical Review Materials

JF - Physical Review Materials

IS - 3

M1 - 035603

ER -