Magnetic snakes control fluids, gravity-defying droplets, and solving a dragonf...( Magnetic Snakes Create Water Curren...)

Magnetic Snakes Create Water Current
M. Belkin, A. Snezhko, I.S. Aranson, and W.-K. Kwok
Physical Review Letters (forthcoming)

Physicists at Argonne National Laboratory have found that magnetic particles suspended in water and subjected to an alternating magnetic field will form snake-shaped structures that can control the flow of the surrounding fluid. Current incarnations of the magnetic snake are a few centimeters long, but the team envisions much smaller versions as pumps to manipulate liquids on microscopic scales or precursors for next-generation magnetic recording media in future computers. The team's recent experiment shows that the speed of the water flowing along the snake depends on how quickly the magnetic field alternates.

To make a magnetic snake, the team put a water-filled beaker at the center of a magnetic coil. In the water, they suspended magnetic nickel spheres a little smaller than one tenth of a millimeter in diameter. These particles reacted to an alternating magnetic field created by the coil. The nickel spheres aligned themselves head-to-tail with nearby particles as though they contained tiny bar magnets.

The movements of the particle chain made waves on the surface of the water, encouraging the formation of parallel chains and causing a segmented pattern. The self-assembly of the snakes can take anywhere from a fraction of a second to several minutes. -KM

Droplets that Roll Uphill
P. Brunet, J. Eggers, and R.D. Deegan
Physical Review Letters (forthcoming)

A recent experiment conducted by physicists at University of Bristol in the United Kingdom has shown that liquid drops can defy gravity. Droplets of liquid on an inclined plate that is shaken up and down can travel uphill rather than sliding down. In fact, if the plate vibrates at the right rate, the droplets will always travel counter-intuitively up the incline.

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