Nanotube inks are inching closer to real-world applications

Nanotube inks have captured the imagination of inventors and scientists worldwide. For years, researchers have been working on methods and materials that turn nanotube inks from lab projects into viable ingredients used in printed circuitry.

Now Chinese scientists from Tsinghua University in Beijing have developed a method to draw nanotube fibers with a pen. Nanotube fiber drawing has been accomplished before, but the nanotubes were comparatively short in earlier attempts – just a fraction of an inch – limiting their use in electronic devices. With the new method, fibers up to 50 centimeters have been shown to be possible, according to the scientists.

The carbon nanotube fibers are put in a solution of polyethylene oxide (PEO), a viscous polymer. The electrically conductive tubes are drawn through the pen by the PEO, a material with significant chemical strength. The ink may be used in flexible electronic devices, including solar cells and touch displays. The scientists hope to develop the fibers further so that they can be used in a variety of commercial applications.

Meanwhile, at the University of Wisconsin at Madison, a multidisciplinary research team headed by Associate Professor Michael Arnold and Professor of Material Science and Engineering Padma Gopalan discovered nanotubes as a possible replacement for silicon-based semiconductors. Carbon nanotubes consist of graphene, a single layer of carbon atoms, rolled into a tube. Graphene is hailed as the new wonder material because of its strength and conductivity. However, working with graphene has its challenges. Due to the way they are formed, using nanoparticles as a starting point, there can be variations in conductivity between nanotubes.

Or, as the scientists from the Tsinghua University Beijing discovered, there may be a change in conductivity under stress. The researchers wanted to confirm that the ultra-long nanotubes maintained their conductivity after bending and twisting. They did. But what they observed surprised the scientists: Instead of a decrease in conductivity, they actually saw a 30 % increase after 1000 bending cycles. The researchers thought it likely that the physical stress improved the nanotube alignment but said that further research is necessary.

The researchers Arnold and Gopalan experimented with ways to separate the desired nanotubes from metallic nanotubes, which also formed during the process. They used an organic solvent and discovered that the semiconducting nanotubes in fact stuck to the solvent, leaving their less desirable metallic counterparts behind. They also devised a way to align the nanotubes on the desired substrate. “By aligning the nanotubes and getting rid of the metallic ones, we have been able to make very efficient nanotubes. And we feel that this technology that we invented could be scaled industrially and it could be the way to start using nanotubes,” said Arnold in an interview.

Linde Electronics has already made great progress in this area. In 2013, the company launched a new carbon nanotube ink to speed up the development of next generation displays and electronic devices. Possible applications include a roll-up-screen for a smartphone or a transparent GPS embedded in the windshield of a car. Linde made the ink available to developers so that they can perfect the processes and methods and develop new applications.

The possibilities are clearly there, as the nanomaterials for printing market is expected to grow from 710 million USD in 2013 to 1.9 billion USD by 2019, according to predictions by Markets and Markets. The report includes not only carbon nanotube inks, a still emerging market, but also more mature markets and includes nanosilver ink, nanogold ink, carbon nanotube ink, copper nanoparticle ink, copper oxide nanoparticle ink, iron oxide nanoparticle ink and a variety of applications ranging from sensors to RFID tags to printed circuit boards.