A nano-device that can repeatedly lifting 165 times its weight easily has been devised by Rutgers University-New Brunswick engineers. The lighter than featherweight device weighs in at 1.6 milligrams but can lift 265 milligrams repeatedly hundreds of times, pointing the way to re-usable actuators for a wide range of nano and micro electromechanical applications, the research suggests.
The device's strength is derived from a process that involves the insertion and removal of ions from in between very thin sheets of crystalline molybdenum disulfide (MoS2). The device parallels the way in which muscles work but represents a new class of actuator that converts electrical into mechanical energy. The team calls it an "inverted-series-connected (ISC) biomorph actuation device" and revealed details in September. [Chhowalla et al., Nature (2017; DOI: XXXXX]
"We found that by applying a small voltage, the device can lift something that's far heavier than itself," explains Manish Chhowalla. "This is an important finding in the field of electrochemical actuators," he adds. "The simple restacking of atomically thin sheets of metallic molybdenum disulfide leads to actuators that can withstand stresses and strains comparable to or greater than other actuator materials."
Actuators are widely used in electromechanical systems and robotics commonly on the macroscale in steerable surgical instruments, in controllers for aircraft wings and even on wind turbines to modulate drag depending on weather conditions. The Rutgers device, just 3 micrometers thick 5 millimeters wide and 60 mm long, rolls up when a voltage is applied. The research was undertaken by Muharrem Acerce and Koray Akdogan.
Naturally occurring molybdenum disulfide is commonly used as a solid-state lubricant in engines because it is a layered material not unlike graphite, but with several advantages over the carbon allotrope for particular applications. There is strong chemical bonding within the thin layers but the layers themselves are only weakly bonded to each other. The team could restack individual "nanosheets" of the material to build their device whereby ion movement between the restacked layers causes the requisite mechanical changes.
The team has demonstrated that their electromechanical system based on molybdenum disulfide has quite extraordinary properties in terms of stress, strain and work capacity way beyond what has been achieved through simpler stacking to form electrodes with only weakly interacting nanosheets.
"The next step is to scale up and try to make actuators that can move bigger things," Chhowalla explains.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.