The transition strength from solid to liquid colloidal dipolar clusters in precessing magnetic fields

Abstract

Abstract. We report on the rotation of colloidal clusters of diamagnetic beads and of mixtures of paramagnetic and diamagnetic beads in a ferrofluid in a precessing external magnetic field. The precession angle of the external field is a control parameter determining the stability of the cluster. Clusters become locally unstable when the local precession angle reaches the magic angle. Cluster shape dependent depolarization fields lead to a deviation of the local from the external precession angle such that close to the external magic angle different cluster shapes might coexist. For this reason cluster transitions are weakly or strongly first-order transitions. If the transition is weakly first order a critical speeding up of the cluster rotation is observed. No speeding up occurs for strongly first-order cluster transitions with hysteresis. The strength of the first-order transition is controlled by the size of the core of the cluster.

Structural variations ahead of crack tip during monotonic and cyclic fracture tests of AISI 304LN stainless steel

“…The cross sections of the specimens, cut with an abrasive cutting machine, were ground and polished with SiC emery paper up to a roughness of 1200 grit and were then polished in cloth with 1 mm diamond paste. To reveal the a 0 -martensite phase, ferrofluid (Ferrotech Corporation EMG 707) was used [27]. A ferrofluid is a water based liquid that contains small magnetic particles with an average diameter of 10 nm.…”

Rotation dynamics and internal structure of self-assembled binary paramagnetic colloidal clusters

“…27 Structural transitions have been investigated in binary mixtures of paramagnetic and diamagnetic colloids under a time-dependent field. 28,29 However, to the best of our knowledge, the dynamics of magnetic colloidal binary clusters in dissipative nonequilibrium conditions have not been previously investigated. Such a study may yield fundamental insights into the assembly of binary systems in biology and bioengineering, such as particle-bacteria biocomposites 30 or hybrid particle-cell aggregates.…”

On demand manipulation of ferrofluid droplets by magnetic fields

“…Dispersions of ferrimagnetic or ferromagnetic particles in the nano/micron-size range have been studied [24][25][26] and water-based ferrofluid droplet systems have been investigated [27][28][29][30]. Ferrofluids are colloidal suspensions of magnetic nanoparticles, coated with a surfactant, in either a water based or oil based carrier fluid.…”