Nanotechnology  

A team researchers in Korea has synthesized carbon nanosheets similar to graphene, using a plastic. The new material is free of the defects and complexity involved in producing graphene, and can substitute for graphene as transparent electrodes for organic solar cells and in semiconductor chips, they say.

Graphene has been dubbed a “wonder material,” and has potential for numerous applications because of the material's great conductivity, flexibility and durability. However, graphene is hard to come by due to the fact that its manufacturing process is complicated and mass production not yet fully achievable.

Now, a Korean research team has developed a carbon material without artificial defects commonly found during the production process of graphene while maintaining thea material's original characteristics. The newly developed material can be used as a substitute for graphene in solar cells and semiconductor chips. Further, the developed process is based on the continuous and mass-produced process of carbon fiber, making it much easier for full-scale commercialization.

The carbon nanosheet can be mass-produced in a simpler process while having high quality since the new process bypasses the steps that are prone to formation of defects such as elimination of the metal substrate or transfer of graphene to another board. The final product is as effective as graphene.

In recognition of the innovative approach, the research was introduced on the cover of Nanoscale, a high impacting peer-reviewed journal in the field of nano science.

The research team led by Dr. Han-Ik Joh at the Korea Institute of Science and Technolgy (KIST) along with Dr. Seok-In Na at Chonbuk National University and Dr. Byoung Gak Kim at KRICT synthesized carbon nanosheets similar to graphene using polymer, and directly used the transparent electrodes for organic solar cells.

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To manufacture high quality graphene in large volume, the CVD (chemical vapor deposition) method is widely used. The technique for manufacturing graphene on the board of metal film that serves as a catalyst. It manufactures the material by blowing out gas called the source gas onto the board. After it is done the metal has to be removed and graphene has to be transported to another board. However, this method requires intensive post-processing (transfer process) as it has to remove used metal after the manufacturing process and move the manufactured graphene to another board such as a solar cell substrate. In this process the quality quickly degrades as it is prone to wrinkles or cracks.

The research team developed “carbon nanosheet” in a two-step process, which consists of coating the substrate with a polymer solution and heating. Considering that the existing process consists of eight steps to manufacture graphene, the new method makes it much simpler. In addition, the new method can be directly used as solar cell without any additional process.

The research team synthesized a polymer with a rigid ladder structure, namely PIM-1(Polymer of intrinsic microporosity-1) to form the CNS through the simpole process, which is spin-coated on the quarts substrates using PIM-1 solution with light green color and then heat-treated at 1,200 °C, leading to transparent and conductive CNS.

The carbon nanosheet can be mass-produced in a simpler process while having high quality since the new process bypasses the steps that are prone to formation of defects such as elimination of the metal substrate or transfer of graphene to another board. The final product is as effective as graphene.

Dr. Han Ik Joh at KIST said, “It is expected to be applied for commercialization of transparent and conductive 2D carbon materials without difficulty since this process is based on the continuous and mass-produced process of carbon fiber.”

This is a follow-up research from the team that recently released its findings on the carbon nanosheet manufacturing based on polyacrylonitrile. The new findings are even more meaningful as it offers deeper understanding on the growth mechanism of carbon nanosheet and much simpler manufacturing process.


SOURCE  KIST

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 Artificial Muscle

MIT researchers at the David H. Koch Institute for Integrative Cancer Research have developed a new material that changes its shape after absorbing water vapor. The film could be used in artificial muscle and to power micro- and nanoelectronic devices.

Researchers at MIT polymer film is expanding and contracting like a muscle, and looks pretty alive doing it, but the energy is coming from water vapor, not black magic. 

The research engineers hope to use the material's continuous motion to generate electricity for nanoelectronic devices, like tiny sensors, or as muscles in robots.

The material is made of two interlocking polymers. One lends structure, while the other swells like a sponge as it absorbs water. In a humid environment, water droplets on a surface under the material cause the film to begin curling. As it moves, air dries the film making it stretch and flip, which exposes it to the moist surface again.

“With a sensor powered by a battery, you have to replace it periodically. If you have this device, you can harvest energy from the environment so you don't have to replace it very often,” says Mingming Ma, a postdoc at MIT’s David H. Koch Institute for Integrative Cancer Research and lead author of a paper describing the new material in the Jan. 11 issue of Science.

Drawing power from humidity is advantageous because water vapor is ubiquitous and relatively easy to control in most environments, at least compared to pH or temperature which have been used in similar experiments.

To generate electricity, the novel film would be combined with a special material that converts the mechanical energy in its movement to electric charge.

It's not a coincidence that the film was developed at MIT's Institute for Integrative Cancer Research. The material, which is very early in development, shows possibilities for biomedical work like targeted drug delivery or physiological monitoring.

SOURCE  MIT

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Duke University engineers have demonstrated for the first time that they can alter the texture of plastics on demand, for example, switching back and forth between a rough surface and a smooth one.

By applying specific voltages, the team has also shown that it can achieve this control over large and curved surface areas.

"By changing the voltage applied to the polymer, we can alter the surface from bumpy to smooth and back again," said Xuanhe Zhao, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering. "There are many instances, for example, when you'd want to be able to change at will a surface from one that is rough to slippery and back again."

Scientists have long been able to create different patterns or textures on plastics through a process known as electrostatic lithography, in which patterns are "etched" onto a surface from an electrode located above the polymer. However, once the patterns have been created by this method, they are set permanently.

"We invented a method which is capable of dynamically generating a rich variety of patterns with various shapes and sizes on large areas of soft plastics or polymers," Zhao said. The results were published online in the journal Advanced Materials.

"This new approach can dynamically switch polymer surfaces among various patterns ranging from dots, segments, lines to circles," said Qiming Wang, a student in Zhao's laboratory and the first author of the paper. "The switching is also very fast, within milliseconds, and the pattern sizes can be tuned from millimeter to sub-micrometer."

The findings follow Zhao's earlier studies, which for the first time captured on videotape how polymers react to changing voltages. Those experiments showed that as the voltage increases, polymers tend to start creasing, finally leading to large craters. This explained in physical terms, for example, why polymers used to insulate electric wires tend to fail over time. The new lithography strategy takes useful insights from this failure mechanism.

On a more fanciful note, Zhao described the possibility of creating rubber gloves whose fingerprints could be changed on demand.

"The changeable patterns we have created in the laboratory include circles and straight and curved lines, which are basic elements of fingerprints," Zhao said. "These elements can be dynamically patterned and changed on a glove surface that covers fingertips.

"A spy's glove may be cool, but probably not for everyone," Zhao said. "However, the same technology can produce gloves with on-demand textures and smoothness tuned for various applications, such as climbing and gripping. Furthermore, surfaces capable of dynamically changing patterns are also useful for many technologies, such as microfluidics and camouflage."

Other potential usages of the new method include creating surfaces that are self-cleaning and water-repellant, or even as platforms for controlled-release drug-eluting devices.




Duke University