Pattern Formation
We are currently investigating pattern formation in a vertically vibrated monolayer of magnetic spheres. The spheres, of diameter D, encase cylindrical magnetic cores of length, l. For large D/l, we find that the particles form a hexagonal-close-packed pattern in which the particles' dipole vectors assume a macroscopic circulating vortical pattern. For smaller D/l, the particles form concentric rings. The static configurational magnetic energy (which depends on D/l) appears to be a determining factor in pattern selection even though the experimental system is driven and dissipative.
Above: Macrovortex Pattern formed by particles with short magnetic cores
Above: Concentric Ring Pattern formed by particles with long magnetic cores.
See our publications page for a Postscript paper about our pattern formation work (to be published)
Polymerization Dynamics
We are also investigating the dynamics of low-density systems of vertically vibrated magnetized spheres in relation to equilibrium polymerization. A wide variety of systems exhibit both ring and chain polymerization under appropriate conditions. Such systems include the polymerization of sulfur and carbon, and the polymerization of tubulin in biological systems. Our vertically vibrated magnetized spheres also show both ring and chain polymerization at appropriate accelerations. We are studying the formation of ring and chain polymers in our system at various driving amplitudes and the transition from a monomeric, gaseous system at high acceleration to a completely connected, polymerized system at low acceleration.
Movie - 16 Particles in a Horizontal 2D System
Segregation
Segregation and pattern formation phenomena in vertically vibrated 2D systems of bidisperse magnetized spheres is currently being investigated. We have observed that particles of equal mass and size, but differing magnetic field strength segregate when driven at appropriate accelerations. We also see segregation in systems of particles of equal mass and equal magnetic strength, but differing magnetic field shape. The segregation rate and pattern formation in the bidisperse mixtures depends upon the vibration amplitude and the number density of each type of particle.
Above: A picture of the initial state of a vertically vibrated 2D system of mixed magnetic spheres. There are 32 yellow and green particles (which have long cylindrical magnetic cores), and 16 blue and green particles (which have short cylindrical magnetic cores). All particles have identical mass and magnetic strength at the pole.
Below: A picture of the final state of a vertically vibrated 2D system of mixed magnetic spheres, after 300 seconds of vibration at 30Hz and 8.9g of acceleration amplitude. The yellow/green particles are almost completely segregated from the blue/green particles (which have short cylindrical magnetic cores). This segregation phenomena is due solely to the shape of the magnetic core.
TO BE CONTINUED - for further information please contact
wlosert@glue.umd.edu.