Scientists have developed a metafluid with programmable response. Scientists at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a programmable metafluid with tunable elasticity, optical properties, viscosity, and even the ability to switch between Newtonian and non-Newtonian fluids.

The first of its kind, the metafluid uses a suspension of tiny elastomeric spheres between 50 and 500 microns in size that bend under pressure, radically changing the properties of the fluid. Metafluid can be used in everything from hydraulic actuators to software robots, to smart shock absorbers that can dissipate energy depending on the intensity of the impact, to optical devices that can go from transparent to opaque. The study was published on: Nature.

“We are just scratching the surface of what is possible with this new class of liquids,” said Adel Jelluli, a research assistant in the department of materials science and engineering at SEAS and first author of the paper. “You can do a lot of different things in a lot of different areas with this one platform.”

Metafluids and solid metamaterials

Metamaterials, artificially engineered materials whose properties are determined by their structure rather than their composition, have been widely used in many applications over the years. But most materials are solid, such as the metal lenses first created in the laboratory of Wynton Hayes, the Federico Capasso Robert L. Wallace Professor of Applied Physics and SEAS Senior Scientist in Electrical Engineering.

“Unlike solid metamaterials, metafluids have a unique ability to flow and conform to the shape of the container they are in,” said Katia Bertholdi, the William and Ami Quan Danoff Professor of Applied Mechanics at SEAS and senior author of the paper. “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.”

Using a scalable manufacturing technology developed in the laboratory of David A. Weitz, the Mallinckrodt Professor of Physics and Applied Physics at SEAS, the research team produced hundreds of thousands of these highly deformed spherical capsules filled with air and suspended in silicone oil. When the pressure inside the liquid increases, the capsules collapse and form a lens-shaped hemisphere. When this pressure is removed, the capsules return to their spherical shape.

Properties and applications of metafluid

This transition changes many properties of the liquid, including its viscosity and opacity. These properties can be adjusted by varying the number, thickness and size of capsules in the liquid.

The researchers demonstrated that fluid programming is possible by loading the metafluid into a hydraulic robotic gripper that holds a glass vial, an egg, and a blueberry. In a traditional hydraulic system powered by simple air or water, the robot needs some sort of sensor or external control so it can adjust its grip and pick up all three objects without crushing them.

However, in metafluid no probe is needed. The fluid itself responds to different pressures and changes its conformation to adjust grip strength to pick up a heavy bottle, a delicate egg, and a small blueberry without additional programming.

“We show that we can use this liquid to give intelligence to a simple robot,” Gelluli said.

The team also demonstrated a fluid logic gate that could be reprogrammed by changing the metafluid.

Optical properties and liquid states

The metafluid also changes its optical properties under the influence of varying pressure. When the capsules are round, they scatter light and make the liquid opaque, similar to how air bubbles turn soda white. But when pressure is applied and the capsules collapse, they act like microlenses, focusing light and making the liquid transparent. These optical properties can be used for a variety of applications, such as electronic inks that change color depending on pressure.

The researchers also showed that when the capsules are spherical, the metafluid behaves like a Newtonian fluid, meaning its viscosity changes only in response to temperature. However, when the capsules collapse, the suspension becomes a non-Newtonian fluid; This means that its viscosity will change in response to shear force; The greater the shear force, the more fluid it is. It is the first metafluid shown to transition between Newtonian and non-Newtonian states.

Next, the researchers try to study the acoustic and thermodynamic properties of the metafluid.

“The scope for these scalable, easy-to-manufacture metafluids is huge,” Bertholdi said.