Paramagnetic colloidal ribbons in a precessing magnetic field

We investigate the dynamics of a kink in a damped parametrically driven nonlinear Klein-Gordon equation.We show by using a method of averaging that, in the high-frequency limit, the kinkmoves in an effective potential and is driven by an effective constant force. We demonstrate that the shape of the solitary wave can be controlled via the frequency and the eccentricity of the modulation. This is in accordance with the experimental results reported in a recent paper [Casic et al., Phys. Rev. Lett. 110, 168302 (2013)], where the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a time-dependent magnetic field has been studied.Ministerio de Economía y Competitividad MTM2012-36732-C03-03 (R.A.N.)Ministerio de Economía y Competitividad FIS2011-24540 (N.R.Q.)Junta de Andalucía FQM262 (R.A.N.)Junta de Andalucía FQM207 (N.R.Q.)Junta de Andalucía FQM-7276Junta de Andalucía P09-FQM-4643 (N.R.Q., R.A.N.)Alexander von Humboldt Foundation (Germany) through Research Fellowship for Experienced Researchers SPA 1146358 STP (N.R.Q.)

Friction-controlled bending solitons as folding pathway toward colloidal clusters

We study the conformational transition of an ensemble of magnetic particles from a linear chain to a compact cluster when subjected to an external magnetic field modulation. We show that the transient dynamics induced by switching the field from static to rotating is governed by the relative friction of adjacent particles in the chain. Solid particles show bending solitons counter-propagating along the chain while buckling of the chain is the mechanism preferred by ferrofluid droplets. By combining real-space experiments with numerical simulations we unveil the underlying mechanism of folding pathways in driven colloidal systems