Scientists develop durable materials for flexible artificial muscles
4×5 inch film made of 10 layers of high performance dielectric elastomer (PHDE) which can be processed and stacked together with 20 actuators. Credit: Software Research Lab/UCLA
UCLA materials scientists and colleagues at the non-profit scientific research institute SRI International have developed new materials and manufacturing processes to create artificial muscles that are stronger and more flexible than their biological counterparts.
“Creating artificial muscles to allow work and detect force and touch has been one of the great challenges of science and engineering,” said Qibing Pei, professor of materials science and engineering at the UCLA Samueli School of Engineering and correspondent author of a recently published study in Science.
For a soft material to be considered for use as an artificial muscle, it must be capable of generating mechanical energy and still be able to withstand high strain conditions—meaning that it does not easily lose its shape and strength after repeated cycles of work. While many materials have been considered competitors for making artificial muscles, dielectric elastomers (DE)—lightweight materials with a high elastic energy density—have received particular attention for their optimal flexibility and toughness.
Dielectric elastomers are electroactive polymers, which are natural or synthetic substances consisting of large molecules that can change size or shape when stimulated by an electric field. They can be used as actuators, enabling machines to operate by converting electrical energy into mechanical work.
Most dielectric elastomers are made of acrylic or silicone, but both have their drawbacks. While traditional acrylic DEs can achieve high actuation strains, they require pre-stretching and are less flexible. Silicone is easier to manufacture, but does not withstand high pressure.
Utilizing commercially available chemicals and using an ultraviolet (UV) light curing process, the UCLA-led research team created an improved acrylic-based material that is more flexible, adjustable, and simpler to scale without losing its strength and durability. While acrylic acid allows more hydrogen bonds to form, thereby making the material more mobile, the researchers also adjusted the cross-links between the polymer chains, allowing the elastomer to be softer and more flexible. A thin, high-performance dielectric elastomer, processable, or PHDE film is then sandwiched between two electrodes to convert electrical energy into motion as an actuator.
Each PHDE film is as thin and light as a human hair, about 35 micrometers thick, and when several layers are stacked together, they become miniature electric motors that can act like muscle tissue and generate enough energy to drive tiny movements. robots or sensors. Researchers have made stacks of PHDE films varying from four to 50 layers.
“These flexible, versatile and efficient actuators could open the gates to artificial muscles in a new generation of robots, or in wearable sensors and technologies that can mimic or even enhance human-like movements and abilities more accurately,” Pei said.
The jumping robot, about 1.2 centimeters in diameter, is equipped with a PHDE actuator. Credit: Software Research Lab/UCLA
Artificial muscles equipped with PHDE actuators can generate more megapascal forces than biological muscles and they also exhibit three to 10 times more flexibility than natural muscles.
Multilayer soft films are usually produced through a “wet” process which involves the deposition and curing of a liquid resin. But that process can result in uneven coating, which makes the actuator underperform. For this reason, to date, many actuators have only had success with single-layer DE films.
UCLA’s research involves a “dry” process in which the film is coated using a knife and then UV-dried to harden, creating a uniform coating. This increases the energy output of the actuator so the device can support more complex movements.
The simplified process, together with the flexible and durable nature of PHDE, has allowed the creation of new soft actuators capable of bending to jump, like spider legs, or winding and turning. The researchers also demonstrated the ability of the PHDE actuator to throw a pea-sized ball 20 times heavier than PHDE film. The actuator can also expand and contract like a diaphragm when voltage is turned on and off, providing a glimpse into how artificial muscles might be used in the future.
These advances could result in soft robots with greater mobility and durability, as well as new wearable and tactile haptic technologies. The manufacturing process can also be applied to other soft thin film materials for applications including microfluidic technology, tissue engineering or microfabrication.
Unimorph nanocomposite dielectric elastomer for large-scale actuation
Ye Shi et al, Processable high performance dielectric elastomers and multilayering processes, Science (2022). DOI: 10.1126/science.abn0099. www.science.org/doi/10.1126/science.abn0099
Provided by the University of California, Los Angeles
Quote: Scientists develop durable materials for flexible artificial muscles (2022, 7 July) retrieved 7 July 2022 from https://phys.org/news/2022-07-scientists-durable-material-flexible-artificial.html
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