Their properties are so peculiar that we hear of metamaterials being created that combine properties that are incompatible in nature, from hardness and flexibility to invisibility, sound insulation, and more. US scientists have done something similar in the field of liquids. Metafluidics created at Harvard can be programmed for specific qualities: change viscosity, transparency, compressive strength, even convert from Newtonian to non-Newtonian and vice versa.

Metamaterials are simple, if you can call it that. Its properties are defined by a well-thought-out structure consisting of smaller components. The shape, size and arrangement of these components allow the propagation of electromagnetic or sound waves to be manipulated, creating force at certain points and relaxation at others. If we take into account the fact that liquids flow and take the shape of a container, metafluids can manifest themselves in places where solid metamaterials have not yet manifested themselves or cannot manifest themselves in principle.

“Unlike solid metamaterials, metafluids have a unique ability to flow and conform to the shape of the container in which they reside. – says the first author of the study, Katia Bertoldi, a scientist from the Harvard School of Engineering and Applied Sciences (SEAS). “Our goal was to create a metafluid that not only has these extraordinary properties but also provides a platform for programmable viscosity, compressibility, and optical properties.”

The metal liquid proposed by the scientists is a suspension of air-filled elastomer balls with diameters between 50 and 500 microns. Tiny balls are placed in a silicone oil solution. If pressure is added to the container containing the balls, when the pressure is released the balls will shrink and return to a round shape. Each of these two states gives the metal fluid its unique properties.

For example, when there is no pressure, the balls remain round and scatter the light falling on them. With the application of pressure, the balls take a flat lenticular shape and begin to transfer the background image. This effect can be used to imagine the operation of colored electronic ink. Or another example is a robotic brush with feedback that allows gentle grasping of fragile objects. The metafluid automatically regulates the compression force, without pressure sensors, thanks only to its ability to react to external pressure: one when picking berries, another when collecting eggs, and the third when lifting weights.

Additionally, the metafluidity proposed by the scientists could switch between Newtonian and non-Newtonian fluids. When the capsules are spherical they are Newtonian, meaning their viscosity changes only with temperature like water, but when they are compressed the liquid becomes non-Newtonian which forces their viscosity to behave according to other laws.

In addition to the above examples, metafluidics can be used to play a logic role in shock absorbers and even water computers that will have the ability to dissipate impact energy. Finally, even the properties of the fictional metafluid can be drastically changed simply by changing the size of the beads inside it, the scientists report in a paper published in the journal Science. Nature.