Metafluids: we had heard about them, but no one had yet managed to make them truly programmable and adaptable like their solid "cousins", the metamaterials. At least until today. A team at Harvard SEAS has developed the first metafluid capable of changing its key physical properties on command, paving the way for countless revolutionary applications in fields such as robotics and optics.
A liquid with “super-powers”
Researchers led by Adel Djellouli e Katia Bertoldi created this innovative metafluid by suspending hundreds of thousands of tiny elastomeric capsules, filled with air, inside silicone oil. When the pressure in the liquid increases, these spheres, ranging in size from 50 to 500 microns, collapse on themselves, taking on a half-lens shape. By removing the pressure, the capsules return to their original spherical shape.
It is precisely this transition that gives the liquid surprising properties. By varying the number, thickness and size of the capsules, parameters such as viscosity, compressibility and even opacity of the fluid can be “tuned”. A real "switch" to transform the metafluid as desired.
Programmable metafluid: intelligent, sensorless liquid robotics
To demonstrate the potential of their programmable metafluid, the researchers tested it on a hydraulic robotic gripper, making it grasp objects very different in shape and resistance: a glass bottle, an egg and a blueberry. Normally, to adapt the grip to such different objects without breaking them, a hydraulic system would require external sensors or controls.
With this “intelligent” liquid, none of this is needed. The liquid itself responds autonomously to the different pressures, varying its compliance to regulate the gripping force based on the object. A first step towards more versatile and adaptable robots, without the need for additional programming.
Transparency on command and other wonders
The surprises don't end there. The Harvard team found that the metafluid also changes its optical properties in response to pressure. When the capsules are spherical, they scatter light, making the liquid opaque, just like air bubbles in sparkling water. But if they are squeezed, they act like micro-lenses, focusing light and making the fluid transparent.
Not only that: at rest the metafluid behaves like a Newtonian fluid, with viscosity influenced only by temperature. However, when the spheres collapse, it becomes non-Newtonian: the more it is subjected to "shear" forces, the more it slides. It is the first metafluid capable of passing from one state to another.
Metafluido, a future full of promises
We are only at the beginning of a fascinating journey. After this research (that I link to you here) the Harvard team is already exploring other properties of their metafluid, such as acoustic and thermodynamic ones. And the potential applications are vast: from hydraulic actuators to programmable robots, from intelligent shock absorbers capable of dissipating energy based on the intensity of the impact, up to optical devices with variable transparency.
A fluid material that combines the advantages of metamaterials with the ability to adapt to the shape of the container. A revolution made possible by an approach as simple as it is ingenious: suspending a myriad of "accordion" capsules in a liquid.
The key to bringing to life a fluid with superpowers, ready to transform the world of robotics, optics and much more.
