Harvard Scientists Have Developed an “Intelligent” Liquid



Harvard researchers have created a programmable and versatile metafluid that can change its properties, including viscosity and optical transparency, in response to pressure. This new class of fluid has potential applications in robotics, optical devices and energy dissipation, representing a significant advancement in metamaterials technology. (Artist’s concept). Credit:

Scientists have developed a metafluid with programmable response.

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

The first metafluid of its kind uses a suspension of small elastomer spheres – between 50 and 500 microns – which deform under pressure, radically changing the characteristics of the fluid. Metafluid could be used in everything from hydraulic actuators to programmed robots, to smart shock absorbers that can dissipate energy based on impact intensity, to optical devices that can switch from clear to dark. opaque.

The research is published in Nature.

“We are only scratching the surface of what is possible with this new class of fluid,” said Adel Djellouli, research associate in materials science and mechanical engineering at SEAS and first author of the paper. “With this one platform, you could do so many different things in so many different areas. »

Metafluids vs solid metamaterials

Metamaterials – artificially made materials whose properties are determined by their structure rather than their composition – have been widely used for years in a variety of applications. But most materials — such as the metal lenses developed in the lab of Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Researcher in Electrical Engineering at SEAS — are strong.

Tunable optics with a Harvard logo displayed below the metafluid. Credit: Harvard SEAS

“Unlike solid

Metamaterials are engineering materials that possess properties not typically found in nature.

” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>metamaterials, metafluids have the unique ability to flow and adapt to the shape of their container,” said Katia Bertoldi, the William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS and senior author of the paper. “Our goal was to create a metafluid that not only possesses these remarkable attributes, but also provides a platform for programmable viscosity, compressibility and optical properties.”

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

Properties and applications of metafluid

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

The researchers demonstrated the liquid’s programmability by loading the metafluid into a hydraulic robotic gripper and having the gripper pick up a glass bottle, an egg, and a blueberry. In a traditional hydraulic system powered simply by air or water, the robot would need some sort of external sensing or control to be able to adjust its grip and pick up all three objects without crushing them.

But with metafluid, no detection is necessary. The liquid itself responds to different pressures, changing its flexibility to adjust the force of the gripper so it can grip a heavy bottle, a delicate egg, and a small blueberry, without additional programming.

“We show that we can use this fluid to endow a simple robot with intelligence,” Djellouli said.

The team also demonstrated a fluidic logic gate that can be reprogrammed by changing the metafluid.

Optical properties and fluid states

The metafluid also changes its optical properties when exposed to changing pressures.

When the capsules are round, they diffuse light, making the liquid opaque, much like air bubbles make aerated water appear white. But when pressure is applied and the capsules collapse, they act like microlenses, focusing the light and making the liquid transparent. These optical properties could be used for various 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, that is, its viscosity only changes in response to temperature. However, when the capsules collapse, the suspension transforms into a non-Newtonian fluid, meaning that its viscosity will change in response to the shear force: the greater the shear force, the more fluid it becomes. It is the first metafluid shown to transition between Newtonian and non-Newtonian states.

The researchers then aim to explore the acoustic and thermodynamic properties of the metafluid.

“The application space for these scalable and easy-to-produce metafluids is enormous,” Bertoldi said.

Reference: “Shell buckling for programmable metafluids” by Adel Djellouli, Bert Van Raemdonck, Yang Wang, Yi Yang, Anthony Caillaud, David Weitz, Shmuel Rubinstein, Benjamin Gorissen and Katia Bertoldi, April 3, 2024, Nature.
DOI: 10.1038/s41586-024-07163-z

Harvard’s Office of Technology Development has protected the intellectual property associated with this research and is exploring commercialization opportunities.

The research was funded in part by the NSF through grant number DMR-2011754 from the Harvard University Materials Research Science and Engineering Center.

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