Editorial Feature

Graphene in 2017: Weekly Research Update, April 18th

This article is the latest in a series summarizing the most current news from the world of graphene - including the latest research into novel applications, commercial developments, and new insights into the material's fundamental physics and chemistry.

Image credit: Shutterstock / OliveTree

Reducing Graphene's Flammability for Safety in Mass Production

The mechanical and physical strength of graphene in each of its applications, in addition to its impressive ability to conduct heat and electricity, continues to generate an enormous amount of excitement from prospective industries.

While the properties of this material have proven so useful in countless applications, its high flammability potential limits its ability to be commercialized at a large-scale level. In an effort to address this limitation, researchers from the University of Arkansas have discovered a method on how to convert graphene oxide into a non-flammable and paper-like graphene membrane that is safe for mass production purposes.

In their study, the group of researchers found that a cross-link between the potentially explosive material, graphene oxide (GO), and aluminum cations (Al3+), forms a highly flexible, nontoxic, mechanically strong and non-flammable carbon-polymer membrane.1

To test its potential to ignite, the researchers exposed the transparent membrane to an open flame, which showed GO to burn out within approximately 5 seconds following this exposure, while the cross-linked membrane was resistant to any in-air burning.2 It is suggested that reactions involving the opening of the epoxy rings within the newly developed membrane occurred on the surface of the GO membrane, allowing for the successful inorganic polymerization of this material to prevent ignition following exposure to a flame.

Researchers are hopeful that this type of membrane with such extraordinary thermal and water stabilities could advance fuel cells that are exposed to particularly high temperatures2, as well as other electronic graphene products that require such a resistant property.

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Graphene FETs for Optical Devices

A wide variety of graphene-based optical devices have recently emerged - however, the sensitivity of this material, particularly when used for the photodetectors in these devices, is becoming a critical aspect of this technology.

Within the optical device, photodetectors are used as a receiver to convert light signals to a voltage, or current, that is able to conduct electricity. Some examples of photodetectors include photodiodes and phototransistors that can be applied to a device, such as a solar cell, to elicit readily available energy. While some graphene-based detectors are available on the market today, their sensitivity to light greatly limits their ability to adequately perform its function.

In an effort to solve this problem, a research team led by Yong Chen at the Purdue University, have combined graphene with silicon carbide substrate in order to create what they termed as graphene field-effect transistors (GFETs), that can exhibit a high performance conversion of light to energy.3

In their model device, a small piece of graphene is placed on a large wafer of silicon carbide in order to achieve a photodetection that is present on a very large surface area. As light enters the device, the phototransistor is “position-sensitive,” which means that it is capable of determining the exact location in which the light is coming.

As this light penetrates the photo carriers present within the un-doped silicon carbide part of the semiconductor, the light therefore becomes partially conductive which changes the electric field of the graphene present in the device.4 The graphene part of the material detects this change in the electric field, which is caused by light photons, that then initiates the interaction between the electric current and the silicon carbide substrate.4

The results of this experiment showed that sensitivity could be achieved in such photo detectors following the application of graphene into these devices, which could advance future projects involving imaging technologies and sensors for high-energy radiation purposes.    

Graphene Coating Can Detect Microcracks to Predict Structural Failure

One of the most challenging tasks that researchers face in the material science world is accurately predicting when structural failure will occur in a given material. It is well understood that mechanical deformations within a material, such as microcracks, has the potential to cause catastrophic failures of many engineered materials.5

Such deleterious effects have been shown to cause airplane wings to fall off and bridges to collapse, and these types of events are often attributed to failures occurring at the nanoscale within the material. Researchers have been diligently working towards developing methods capable of detecting the warning signs of possible structural defects prior to the actual failure of the material.

A group of researchers from Leibniz Institute of Polymer Research in Germany recently hypothesized that the structural correlation in composite interphases can allow for a visualization of microcracks within a material when coated with a specific optical reflector. This optical reflector is comprised of fine and overlapping parallel layers of graphene nanoplatelets (GNPs) that are placed on a single glass fiber surface.5

The native state of this graphene coating exhibits a red color, however, any alteration in the material causing it to bend in or out will cause the material to change yellow. Similarly, any crack within the material, which is apparent when cleaves between the flakes are shown, will cause the material to exhibit a green color. This highly visible change in the coloration of the material makes it relatively easy for any individual, trained or not, to visualize any damage present within the material.5

While further testing is necessary to determine the complete effectiveness of such an application, this graphene coating has a promising future in ensuring the safety of many industrial materials.

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References

  1. Non-flammable Graphene Membrane Developed for Safe Mass Production - University of Arkansas News
  2. “Multivalent Cation Cross-Linking Suppresses Highly Energetic Graphene Oxide’s Flammability”, Hulusi Turgut, Z. Ryan Tian, Fengjiao Yu, and Wuzong Zhou, J. Phys. Chem. 2017, DOI:10.1021/acs.jpcc.6b13043
  3. Graphene 'Phototransistor' Promising for Optical Technologies - Purdue University Newsroom
  4. "Position-dependent and millimetre-range photodetection in phototransistors with micrometre-scale graphene on SiC", Biddut K. Sarker et al, Nature Nanotechnology, 2017, DOI:10.1038/nnano.2017.46
  5. "Variable Structural Colouration of Composite Interphases",  Y. Deng et al, Mater. Horiz. 2017, DOI:10.1039/C6MH00559D

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