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

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 35; no. 3; pp. 1 - 6
• Main Authors: Ray, A., Fischer, Th. M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-03-2012; EDP Sciences
• Subjects: Biological and Medical Physics; Biophysics; Chemistry; Colloidal state and disperse state; Complex Fluids and Microfluidics; Complex Systems; Exact sciences and technology; General and physical chemistry; Nanotechnology; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Soft and Granular Matter; Surfaces and Interfaces; Thin Films; Soft Matter: Colloids and Nanoparticles; Magic angle; Magnetic field effect; External field; Liquid; Shape; Stability; Aggregate; Rotation; Colloid; Hysteresis; Colloid particle; Solid
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2012-12017-x

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.