Magnetic-field-induced optical transmittance in colloidal suspensions

Abstract

Through simulation and experiment we demonstrate that when a magnetic field is applied to a suspension of magnetic particles, the optical attenuation length along the direction of the field increases dramatically, due to the formation of chainlike structures that allow the transmission of light between the strongly absorbing particles. This phenomenon is interesting for two reasons; first, there might be practical applications for this effect, such as optical-fiber-based magnetic field sensors, and second, measuring the time evolution of the optical attenuation length enables us to determine the kinetics of structure formation, which can be compared to the predictions of simulation and theory. In agreement with both simulation and theory, the optical attenuation length increases as a power of time, but much less light is actually transmitted than expected, especially at higher particle concentrations. We conclude that particle roughness, which is not included in either theory or simulation, plays a significant role in structural development, by pinning structures into local minima.

Aggregation of paramagnetic particles in the presence of a hydrodynamic shear

“…Furthermore, such forces can be monitored easily by changing the externally applied field. Experiments dealing with magnetic and dielectric aggregation in the case of perikinetic aggregation (i.e., in a fluid at rest) have been undertaken by several investigators [11][12][13][14][15]. These experiments resulted in consistent well-controlled data and, as a whole, confirmed Smoluchovski theory to a good degree of accuracy as long as the delicate hydrodynamic interaction between clusters is properly taken into account.…”

Physical Properties of Magnetic Fluids and Nanoparticles from Magnetic and Magneto-rheological Measurements

“…Chain-like clusters are supposed to form (which usually have up to tens of particles per aggregate (2)). Thick chains which can form according to (27) are not excluded, but have a low probability. The magnetoviscous effect (Fig.…”

In SituImaging of Field-Induced Hexagonal Columns in Magnetite Ferrofluids

“…Thermal fluctuations [15], defective chains [17], or chain bending in general [18] can induce variations in the dipole moment density and, consequently, long-range coupling between one-dimensional structures in colloidal dispersions. In system A, fluctuations in the dipole moment density must be important, particularly in view of the initial particle configuration in zero field (Fig.…”