Controlled disassembly of colloidal aggregates confined at fluid interfaces using magnetic dipolar interactions.

HYPOTHESIS

Field induced assembling/disassembling of paramagnetic colloids is strongly influenced by the configuration of the applied field, the surface chemistry of the particles, the nearby presence of an external boundary or the particle density. The trapping of the particles at fluid-fluid interface is expected to promote different assembling/disassembling routes together with new approaches for controlled manipulation of self-assembled structures and the fabrication of new functional patterned surfaces.

EXPERIMENTS

We study the reversible disassembly itineraries that emerge in linear aggregates of micrometer-sized magnetic particles adsorbed onto a fluid interface when the applied field is abruptly tilted out of the confining surface: the unzipping of chains laterally aggregated, the partial fragmentation of the chains, the gradual separation of the monomers and the abrupt colloidal explosion.

FINDINGS

By combining experiments, simulations and theoretical arguments, we elucidate different dissociation mechanisms strongly influenced by subtle changes in the orientation of the applied field, the particle's position relative to the confining interface and the mutual induction of the particles. Moreover, we show that the understanding of the mechanisms can be applied to pinpoint exactly particle detachments in two-dimensional binary mixtures.