AI News, Moisture-responsive 'robots' crawl with no external power source

Moisture-responsive 'robots' crawl with no external power source

'The development of smart materials such as moisture-responsive graphene oxide is of great importance to automation and robotics,' said Yong-Lai Zhang of Jilin University, China, and leader of the research team.

In the journal Optical Materials Express, from The Optical Society (OSA), the researchers reported that graphene oxide sheets treated with brief exposure to bright light in the form of a camera flash exhibited reversible bending at angles from zero to 85 degrees in response to switching the relative humidity between 33 and 86 percent.

Although other materials can change shape in response to moisture, the researchers experimented with graphene-based materials because they are incredibly thin and have unique properties such as flexibility, conductivity, mechanical strength and biocompatibility.

For example, the material's excellent biocompatibility could allow moisture-responsive graphene oxide to be used in organ-on-a-chip systems that simulate the mechanics and physiological response of entire organs and are used for drug discovery and other biomedical research.

When moisture is present, the reduced side of the graphene oxide absorbs fewer water molecules, causing the non-reduced side to expand and the sheet to bend toward the reduced side.

Jiaxing Huang Group

Graphite oxide sheets, now called graphene oxide (GO), are typically made from chemical exfoliation of graphite by reactions that have been known for 150 years.

We first entered this research area with a curiosity-driven hypothesis to study GO as an unconventional type of soft material, such as a 2D polymer, highly anisotropic colloid, membrane, liquid crystal, and amphiphile.

To mitigate the fire risk of GO, especially during large scale production, we developed a procedure to suppress its gelation during washing and thus greatly increased the throughput of sample purification.

This can be done using the Xenon flash lamp on a camera, which has sufficient energy to trigger the exothermic deoxygenation reaction of GO, and photothermally heat up the reduced GO to weld it with polymer particles.

Such metal contaminants can be introduced unintentionally during the synthesis and processing of GO, most notably on filtration with anodized aluminium oxide (AAO) filter discs that corrode to release significant amounts of Al3+.

This finally solves the puzzle of the stability of GO films in water. This finding also helps to better understand the mechanical properties of GO thin films and some other puzzles about ionic cross-linking of GO films.

It was also discovered that the amphiphilicity of GO is dependent on its size and pH, which allows the microstructures (e.g., wrinkles and overlaps) of such GO monolayers to be tuned to optimize the optoelectrical properties of the resulting graphene monolayers.

The size-dependent amphiphilicity of GO motivated us to synthesized its nanocolloids by chemically exfoliating commercial graphite nanofibers, in which the graphene sheets are coin-stacked along the fiber length. In this way, the upper size limit of the resulting GO nanocolloids (c.a. tens of nanometers) is predetermined by the fiber diameters, leading to much more uniform and controllable later dimensions than fracturing-based size-reduction process.

GO/SWCNTs thin films can replace the corrosive conducting polymer based interfacial layers used in organic solar cells for both single layer and tandem architectures.

In the presence of minute amount of GO (e.g., 0.1 wt%), carbonization proceeds much faster and yields more conductive carbon materials with high electrochemical specific capacitance comparable to graphene-based materials themselves.

Ultra Highly Concentrated Single-Layer Graphene Oxide, 60 ml

Ultra Highly Concentrated formula of Single-Layer Graphene Oxide Flakes Properties: Centrifugation has been used to prepare extra-large flakes and get an ultra-high concentration of Graphene Oxide.

The ultra-highly concentrated graphene oxide forms paper-like substances and will coat virtually any surface, including the bottle itself.

Production of Graphene Oxide: Graphene Oxide is the oxidized form of graphene produced by oxidizing crystal graphite with a mixture of sulfuric acid, sodium nitrate, and potassium permanganate (the Hummers method).

Brown University

[Brown University] — Crumple a piece of paper and it’s probably destined for the trash can, but new research shows that repeatedly crumpling sheets of the nanomaterial graphene can actually enhance some of its properties.

The research by engineers from Brown University shows that graphene, wrinkled and crumpled in a multi-step process, becomes significantly better at repelling water—a property that could be useful in making self-cleaning surfaces.

The team had previously showed that by introducing wrinkles into graphene, they could make substrates for culturing cells that were more similar to the complex environments in which cells grow in the body.

“As you go deeper into the generations you tend to get larger wavelength structures with the original, smaller wavelength structure from earlier generations built into them,” said Robert Hurt, a professor of engineering at Brown and one of the paper’s corresponding authors.

The material has a ‘memory’ and we get different results when we wrinkle or crumple in a different order.” The researchers generated a kind of taxonomy of structures born from different shrinking configurations.

When the contact angle of those water beads with an underlying surface exceeds 160 degrees—meaning very little of the water bead’s surface touches the material—the material is said to be superhydrophobic.

The research showed that crumpled graphene used as a battery electrode had as much as a 400 percent increase in electrochemical current density over flat graphene sheets.

“You just need to crumple the graphene.” In additional to batteries and water resistant coatings, graphene compressed in this manner might also be useful in stretchable electronics—a wearable sensor, for example.

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