Biomorph Actuator Lifts 165 Times its Own Weight
The Engineer posted on August 30, 2017 |
This tiny device--3-micrometer thick and 0.5 centimeters wide and 6 centimeters (about 2.4 inches) long -- rolls up when voltage is applied. Created by materials scientists at Rutgers University-New Brunswick, it gains strength from the insertion and removal of ions between atomically thin nanosheets of a crystalline compound. (Image courtesy of Muharrem Acerce/Rutgers University-New Brunswick.)

This tiny device—3-micrometer thick, 0.5 centimeters wide and 6 centimeters long—

rolls up when voltage is applied. (Image courtesy of Muharrem Acerce/Rutgers University-New Brunswick.)
Imagine repeatedly lifting 165 times your weight without breaking a sweat—a feat normally reserved for superheroes like Spider-Man.

Rutgers University-New Brunswick engineers have discovered a simple, economical way to make a device that can match your friendly neighborhood webslinger, only on a much smaller scale. Their creation weighs 1.6 milligrams but can lift 265 milligrams hundreds of times in a row.

Its strength comes from a process of inserting and removing ions between very thin sheets of molybdenum disulfide (MoS2), an inorganic crystalline mineral compound to create a new type of actuator.

The Rutgers discovery—called an "inverted-series-connected (ISC) biomorph actuation device"—is described in a study published online in the journal Nature.

"We found that by applying a small amount of voltage, the device can lift something that's far heavier than itself," said Manish Chhowalla, professor and associate chair of the department of materials science and engineering. "This is an important finding in the field of electrochemical actuators. The simple restacking of atomically thin sheets of metallic MoS2 leads to actuators that can withstand stresses and strains comparable to or greater than other actuator materials."

Nanosheets of molybdenum disulfide (a) and schematics and photos of working biomorph actuators. (Image courtesy of Muharrem Acerce/Rutgers University-New Brunswick.)
Nanosheets of molybdenum disulfide (a) and schematics and photos of working biomorph actuators. (Image courtesy of Muharrem Acerce/Rutgers University-New Brunswick.)
Actuators are used in a wide variety of electromechanical systems, with applications such as steerable catheters, aircraft wings that adapt to changing conditions and wind turbines that reduce drag.

Molybdenum disulfide is commonly used as a solid-state lubricant in engines. It's a layered material like graphite, with strong chemical bonding within thin layers but weak bonding between the layers. Thus, individual layers of MoS2 can be easily separated into individual thin sheets via chemistry.

These nanosheets remain suspended in solvents such as water and can be assembled into stacks by putting the solution onto a flexible material and allowing the solvent to evaporate. The restacked sheets can then be used as electrodes with high electrical conductivity to insert and remove ions.

Inserting and removing ions leads to the expansion and contraction of nanosheets, resulting in force on the surface. This force triggers the actuation of the flexible material.

Chhowalla and his team report that their MoS2-based electrochemical device has extraordinary mechanical properties such as stress, strain and work capacity, especially considering the electrodes are made by simply stacking weakly interacting nanosheets.

"The next step is to scale up and try to make actuators that can move bigger things," Chhowalla said.

For another amazing application of MoS2, find out how the Smallest Transistor Ever Ditches Silicon to Achieve 1-Nanometer Gate.

Source: Rutgers University

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