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Light-driven artificial muscle made with nanomaterials

Posted By Graphene Council, The Graphene Council, Monday, April 22, 2019
Updated: Saturday, April 20, 2019

Reporting their findings in Advanced Materials ("Plasmonic-Assisted Graphene Oxide Artificial Muscles"), researchers in China have developed a plasmonic-assisted holistic artificial muscle that can independently act as a fully functional motor system without assembling or joints.

The artificial muscle's low-cost integrated design consists of a composite layer uniform bilayer configuration made of gold nanorods embedded in graphene oxide or reduced graphene oxide and a thermally expansive polymer layer (PMMA).

The gold nanorods of varying aspect ratios endow the graphene nanocomposites with tunable wavelength response. This enables the fabrication of a light-sensitive artificial muscle that can perform complex limb-like motions without joints.

Combining the synergistic effect of the gold nanorods' high plasmonic property and wavelength selectivity with graphene's good flexibility and thermal conductivity, the artificial muscle can implement full-function motility without further integration, which is reconfigurable through wavelength-sensitive light activation.

Upon photothermal heating, the mismatch between the deformations of two layers leads to significant bending, replicating the muscle-like contraction from one layer and expansion from the other.

To demonstrate the light-addressable manipulation of complicated multiped robot, the team developed a holistic spider robot.

They patterned each leg of the spider with three nodes (see figure g above). Despite that the spider has been patterned on 2D film, it can deform into 3D structures under light irradiation due to the bending of its legs.

When the laser beam irradiates the legs one by one, the legs bend one after another, which induced the displacement of the gravity center of the spider accordingly. In this way, the researchers could control the spider robot to lean forward and move toward the right direction at an average speed of 2.5 mm per second.

The authors conclude that their work bridges the gap between ideal request and realistic restrictions of biomimetic motor systems, and decreases the amount of discrete parts, the number of postprocessing steps, and the fabrication time, and thereby offers new opportunities for biological aid and for biomimetic mini robots to be remotely operated.

Tags:  artificial muscle  Graphene  graphene oxide  nanocomposites 

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Graphene Lays Foundation for Fast Charging High Capacity Li-ion Batteries

Posted By Dexter Johnson, IEEE Spectrum, Thursday, June 14, 2018

Prof. Dina Fattakhova-Rohlfing. (Image: FZ Juelich)

Graphene has been earmarked for energy storage applications for years. The fact that graphene is just surface area is very appealing to battery applications in which anodes and electrodes store energy in the material that covers them.

With lithium ion (Li-ion) batteries representing the most ubiquitous battery technology, with uses ranging from our smart phones to electric cars, increasing their storage capacity and shortening their charging times with graphene has been a big research push. 

Unfortunately, the prospects for graphene in energy storage have been stalled for years. This is in part due to the fact that while graphene is all surface area, in order to get anywhere near the kind of storage capacity of today’s activated carbon you need to layer graphene. The result after enough layering is you end up back with graphite, defeating the purpose of using graphene in the first place.

Now a team of German researchers has developed an approach for improving the anodes of Li-ion batteries that uses graphene in support of tin oxide nanoparticles.

"In principle, anodes based on tin dioxide can achieve much higher specific capacities, and therefore store more energy, than the carbon anodes currently being used. They have the ability to absorb more lithium ions," said Dian Fattakhova-Rohlfing, a researcher at Forschungszentrum Jülich research institute in Germain, in a press release. "Pure tin oxide, however, exhibits very weak cycle stability – the storage capability of the batteries steadily decreases and they can only be recharged a few times. The volume of the anode changes with each charging and discharging cycle, which leads to it crumbling."

The research described in the Wiley journal Advanced Functional Materials, uses graphene as a base layer in a hybrid nanocomposite in which the tin oxide nanoparticles enriched with antimony are layered on top of the graphene. The graphene provides structural stability to the nanocomposite material.

The combination of the tin oxide nanoparticle being enriched with antimony makes them extremely conductive, according to Fattakhova-Rohlfing. "This makes the anode much quicker, meaning that it can store one-and-a-half times more energy in just one minute than would be possible with conventional graphite anodes. It can even store three times more energy for the usual charging time of one hour."

The scientists found that in contrast to most batteries the high energy density did not have to come with very slow charging rates. Anybody who has a smartphone knows how long it takes to charge it to 100 percent.

"Such high energy densities were only previously achieved with low charging rates," says Fattakhova-Rohlfing. "Faster charging cycles always led to a quick reduction in capacity."

In contrast, the research found that their antimony-doped anodes retain 77 percent of their original capacity even after 1,000 cycles.

Because tin oxide is abundant and cheap, the scientists claim that the nanocomposite anodes can be produced in an easy and cost-effective way.

Fattakhova-Rohlfing added: "We hope that our development will pave the way for lithium-ion batteries with a significantly increased energy density and very short charging time."

Tags:  energy storage  Li-ion batteries  nanocomposites  nanoparticles 

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