Scientists at US Rice University have demonstrated that laser-induced graphene can be applied to a number of substances in air. This is a development with applications for issues such as food security.
A Rice University laboratory uses a laser to burn graphene in the form of a Rice Owl into a piece of cloth pre-treated with fire retardant that turns the surface into amorphous carbon.
The technique created at Rice allows conductive laser-induced graphene to be created on many surfaces. The scientists who have introduced laser-induced graphene (LIG) have developed their technique to produce. "This is not ink," chemist James Tour of Rice University said. "This is taking the material itself and converting it into graphene."
This process is an extension of the Tour's laboratory's argument that anything with the proper carbon content can be converted into graphene. The laboratory has developed and expanded on its method to make graphene foam by using a commercial laser to change the top layer of a not-costly polymer film in the recent years
The foam is made up of microscopic, cross-linked flakes of graphene, the two-dimensional form of carbon. LIG can be written into target materials in patterns.
Potential for biological sensors
Its potential applications include being used as a supercapacitor, an electrocatalyst for fuel cells, radio-frequency identification (RFID) antennas and biological sensors. The new work was reported in the American Chemical Society journal, ACS Nano. It showed that laser-induced graphene can be burned into paper, cardboard, cloth, coal and certain foods, even toast.
"Very often, we don't see the advantage of something until we make it available," Tour said. "Perhaps all food will have a tiny RFID tag that gives you information about where it's been, how long it's been stored, its country and city of origin and the path it took to get to your table."
He said LIG tags could also be sensors that detect E. coli or other microorganisms on food.
"They could light up and give you a signal that you don't want to eat this. All that could be placed not on a separate tag on the food, but on the food itself." Tour said. The researchers could write LIG patterns into cloth, paper, potatoes, coconut shells and cork, as well as toast. (The bread has to be toasted first to carbonize the surface.) using multiple laser passes with a defocused beam.
Defocusing the laser necessary
"In some cases, multiple lasing creates a two-step reaction," Tour said. "First, the laser photothermally converts the target surface into amorphous carbon. Then on subsequent passes of the laser, the selective absorption of infrared light turns the amorphous carbon into LIG. We discovered that the wavelength clearly matters."
The researchers had to use multiple lasing and defocusing when they discovered that increasing the laser's power didn't make better graphene on a coconut or other organic materials. Defocusing the laser accelerated the process for many materials as the wider beam allowed each spot on a target to be lased many times in a single scan.
That also allowed for fine control over the product, Tour said. Defocusing allowed them to turn previously unsuitable polyetherimide into LIG. Flexible, wearable electronics may be an early market for the technique. "This has applications to put conductive traces on clothing, whether you want to heat the clothing or add a sensor or conductive pattern," he said.