Annoying folds that give graphene new life?

Material cow note:[ Brown University] Crumple a piece of paper, it is probably destined to be thrown to the trash can; However, new research shows that repeatedly kneading graphene, a Nano material, can enhance some of its properties. In some cases, even wrinkles are better.

Engineering studies at Brown University have shown that graphene has significantly improved its hydrophobic properties after multiple folds -- a property that is helpful when making clean surfaces. Folded graphene also has enhanced electrochemical properties, which may be more advantageous for batteries and fuel cell electrodes.

The results were published in the journal Advanced Materials.

[Folding Times]

Engineering researcher at Brown University: Robert Hurt and Ian Wong, two previous works have laid a good foundation for this study. The team earlier said that by introducing creases to graphene, they could turn the substrate used to grow cells into a more complex environment in the body. For this latest result, a postdoctoral research team leader, Professor Po-YenChen, said he wanted to build complex structures that combine folds. "I wanted to see if there was any chance of creating a higher hierarchy," Chenjiaoshou said.

To do this, the researchers deposited graphene oxide onto the shrink membrane -- a property that uses the polymer membrane to contract when heated. When the film contracts, the graphene at the top is compressed, causing it to fold. In order to see what kind of fold structure would be produced, the researchers repeated compression of the same graphene. After the first contraction, the membrane is dissolved and graphene is placed in another new membrane to continue.

In several successive contractions, the researchers tested a number of different configurations. Sometimes, for example, they hold the opposite end of the film, allowing them to contract only along a single axis. The periodic graphene layer produced by the fixed film, basically parallel folds will spread over its surface. The unclamped film contracts in two dimensions, the XY direction, resulting in a random and wrinkled graphene surface.

The team also used different contraction patterns to test several successive tests. For example, they might contract the same graphene, first by clamping the film, then without clamping, and finally by clamping. Or left unclamped, clamped, unclamped. They also rotate graphene between different configurations of contraction, sometimes making it perpendicular to the original direction.

The team found that this continuous contraction could greatly compress graphene sheets, reducing them to one-fortieth of their original size. They also said that the method can create interesting patterns along the surface, for example: folds can be superimposed on each other.

When you go deeper, you see larger corrugated structures that contain the original little corrugated structures that were left behind, said Robert Hurt, a professor at Brown University's School of Engineering and one of the authors of the paper's newsletters. "

This contraction is first clamped, released, and then clamped; The other is not clip, clip, and then release. The two obviously look different. The order of operation will determine the final structure, said Professor Wang, the author of another paper. " This is not like multiplying two times three is equivalent to three times two. The material has" memory "and it will have different results when we use different contraction sequences. "

The researchers came up with a structural classification derived from different contraction configurations. They then tested several structures to see how they changed the properties of the graphene layer.

[Enhanced characteristics]

The researchers found that a crumpled graphene surface becomes super-hydrophobic -- preventing it from sticking to the surface. When water comes into contact with a hydrophobic surface, water droplets are formed and slipped(when the contact angle between these beads and the surface exceeds 160 degrees -- meaning that very few water beads can touch the material -- the material is considered to be super hydrophobic). The researchers found that they could make superhydrophobic graphene out of three loose shrinkage folds.

The team also found that folds can increase the electrochemical properties of graphene, which is beneficial to the next generation of energy storage and production equipment. Studies have shown that compared to the flat graphene layer, if the folded graphene layer is used as a battery electrode, the electrochemical current density will be increased by 400 %. Its increase in current density will create more efficient batteries.

"You don't need a new material," says Chenjiaoshou. "You just need to wrinkle the graphene." "

In addition to batteries and waterproof coatings, this compression method of graphene may also be suitable for Yuke's stretched electronic device, the wearable sensor.

The group plans to continue to make structures on graphene and other nanomaterials using different production methods.

Not only graphene, but there are many new two-dimensional nanomaterials that have some interesting properties, Wang said. " Therefore, other materials or composites can also form special structures with unexpected functions. "

The study was supported by a seed fund from Brown University. Chenbaoyan is sponsored by the Hibbit Engineering Fellows Program. They support outstanding postdoctoral researchers so that they can make a smooth transition to the establishment of an independent company. Jaskiranjit Sodhi, Yang Qiu, Thomas M. Valentin, RubenSpitz Steinberg and Dr. ZongyingWang are the co-authors of the paper.

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