Micrometric magnetic swimmers: Phenomenology and dynamic characterization

C. E. CHILIOTTE; G. A. JORGE; M. LLERA; V. BEKERIS

La Plata

Workshop; Workshop on Statistical Mechanics of Swarming Behaviour; 2019

Recently, the phenomenology of magnetic particles in aqueous media subject to external excitations has drawn strong attention. The way in which these systems move and self-organize, particularly under time-dependent excitations, has been studied in several works, and the results are of great interest both from the point of view of basic physics and of technological applications. Time-dependent magnetic fields have been used to assemble magnetic non active material in a variety of structures and to propel microscopic matter in a fluid medium in motile structures. Arrays might yield highly desired additional degree of control over their properties and satisfy the rising demand for the design of artificial externally controlled structures. We address in this work different arrangements of magnetic particles dispersed in a fluid where they sediment due to reduced surface tension and density mismatch. We use three Helmholtz coils to generate variable magnetic fields in time and space. Differents magnetic field configurations are applied to move micrometer nickel particles located at the bottom of the container. We study the time dependent displacement of these particles through the analysis of video-microscopy images. Depending on the different configurations of the magnetic field, a variety of mobile structures are obtained, from individual particles, rotating columns, rollers, to jointed structures, which interact with each other and with the container?s bottom by means of hydrodynamic and magnetic interactions. The system of magnetic swimmers is registered, and studied through the analysis of the microscopy images, from which different dynamic indicators are obtained.