University of Massachusetts Amherst researchers have discovered a surprising “shape-changing” liquid that seems to bend the laws of thermodynamics.
The strange compound—made of oil, water, and magnetic nickel particles—was first assembled by a graduate student who was merely curious to see what might happen. To his surprise, when the liquid was shaken, the magnetic particles quickly reformed into a shape resembling a Greek urn.
Emulsion and Thermodynamics
“Imagine your favorite Italian salad dressing,” says Thomas Russell, Silvio O. Conte Distinguished Professor of Polymer Science and Engineering at UMass Amherst and one of the paper’s senior authors. “It’s made up of oil, water and spices, and before you pour it onto your salad, you shake it up so that all the ingredients mix.”
While water and oil normally separate, they can combine through a process called emulsion, where small bits of a third material enter the mix, reducing surface tension between the two normally incompatible substances. The emulsion process works as described by the laws of thermodynamics.
Playing Around in the Lab
A wide range of technologies and applications make use of emulsification. While experimenting with emulsions in the lab, UMass Amherst graduate student Anthony Raykh mixed magnetized nickel with oil and water just to see what might happen.
“Because you can engineer all sorts of interesting materials with useful properties when a fluid contains magnetic particles,” says Raykh. “And, in a complete surprise, the mixture formed this beautiful, pristine urn-shape.”
Despite repeated, vigorous shaking, the mixture consistently returned to a shape resembling an urn. Even altering the size of the magnetic particles did not change the effect.
“I thought ‘what is this thing?’ So, I walked up and down the halls of the Polymer Science and Engineering Department, knocking on my professors’ doors, asking them if they knew what was going on,” Raykh continued.
None of the UMass Amherst researchers could immediately explain the phenomenon. Two of Raykh’s professors, David Hoagland and Thomas Russell, took an interest and joined the investigation.
Investigating a Perplexing Liquid
As the small team began conducting experiments, they expanded their collaboration to include researchers from Tufts and Syracuse universities for help with simulations. The growing team of experts across the Northeast ultimately concluded that strong magnetism was behind the liquid’s unusual behavior.
“When you look very closely at the individual nanoparticles of magnetized nickel that form the boundary between the water and oil,” says Hoagland, “you can get extremely detailed information on how different forms assemble. In this case, the particles are magnetized strongly enough that their assembly interferes with the process of emulsification, which the laws of thermodynamics describe.”
The liquid’s magnetic action reverses the normal emulsion process. Instead of decreasing the tension between oil and water, as normally occurs when introducing a third particle, the magnets increase the surface tension. As a result, the boundary separating the oil and water forms a curve.
Hellbound and Down 