Translational and rotational dynamics in suspensions of magnetic nanorods

Abstract

Using computer simulations we investigate the translational and rotational diffusion of dilute suspensions of magnetic nanorods with and without a (homogeneous) external magnetic field. The magnetic rods are represented as spherocylinders with a longitudinal point dipole at their center and length-to-breadth ratiosIn the absence of a field, the rods tend to form compact clusters with antiparallel ordering and thus behave very differently to dipolar spheres (L/D ¼ 0), which tend to form head-to-tail chains. Furthermore, for rod-like particles the external field tends to destabilize rather than to support cluster formation. We show that these differences in the aggregation behavior have profound consequences not only in static material properties such as the field-induced magnetization and the zero-frequency susceptibility, but also in the dynamics. In particular, for magnetic rods the translational diffusion constant parallel to the field is larger than the perpendicular one, in contrast to the behavior observed for magnetic spheres. Moreover, the rod-like character greatly affects the shape and the density dependence of the single-particle and collective dipole-dipole time correlation functions and their counterparts in the frequency domain.

Steady states of non-axial dipolar rods driven by rotating fields

“…For β = 1, the exponential decay is characteristic of Debyelike relaxation, however, the behavior of the autocorrelation deviates from the Debye-decay, since we obtained, for all cases , β < 1. Similar non-Debye behaviour was also obtained for a 3D systems of magnetic spherocylinders [47].…”

Revealing the signature of dipolar interactions in dynamic spectra of polydisperse magnetic nanoparticles

“…The latter is known to differ significantly from the so-called Langevin law, even for the systems where the dipolar interactions have the same order as thermal fluctuations. 29 Stronger interparticle or intermolecular interactions can lead to a broad range of structuring 30,31 and selfassembly 11,[32][33][34][35] in soft matter, which cannot but affect the dynamics of these systems. Several attempts to incorporate the dipole-dipole interaction into the theoretical description of dynamic spectra are known.…”

Fission and fusion scenarios for magnetic microswimmer clusters

“…An important example for the former are magnetic dipole moments which enable to actuate and control the swimming path by an external magnetic field [13][14][15][16][17][18][19][20][21]. In the absence of swimming, the structure of two-dimensional [22,23] and three-dimensional [24,25] dipole clusters has been explored recently, but the impact of activity on a swimmer cluster has been rarely studied [19,26]. Recent simulation studies [27,28] have revealed that the mean cluster size crucially depends on the strength of the selfpropulsion speed.…”