Self-assembly into ordered, energy-minimizing configurations underlies crystallization, block-copolymer microphase separation, and protein folding, and is being pursued for bottom-up fabrication of nanostructures. But many systems, most notably in biology, are not in equilibrium; instead, they organize themselves in a dissipative state that’s sustained through a continuous supply of energy. Such dynamic systems have proven challenging to understand and engineer. But researchers at Finland’s Aalto University and at ESPCI in Paris have now presented a model system for visualizing and studying self-assembly and complexity over a broad range of conditions.
The system consists of droplets of magnetic ferrofluid on a superhydrophobic surface. The extremely low friction frees the droplets to respond to an external magnetic field. To create this seven-droplet arrangement, for example, the researchers place a single 20-µL drop of ferrofluid on the surface and slowly raise a cylindrical magnet under the substrate. As the fluid experiences increasingly stronger fields...
