Nanotubes continue to capture the imagination of researchers.
Since the features of carbon nanotubes were first identified more than 25 years ago, high expectations have accompanied these single-walled structures. They offer exceptional tensile strength, useful optical properties and thermal and electrical properties that should make them suitable for all manner of novel applications, such as durable, flexible transistors, photovoltaics or biosensors.
Unfortunately, these expectations have not been met because there has been no efficient method of separating semiconducting nanotubes — those suitable for use in transistors — from metallic nanotubes, which have a distinctively different set of characteristics. McMaster University chemistry professor Alex Adronov has been examining various aspects of this problem over the past decade, during which time he has been assembling the expertise and equipment for a closer look at the fundamental interactions that take place between these two types of nanotubes. “We came up with a hypothesis where opposites attract,” Adronov says. “A lot of polymers had already been shown to interact very selectively with semiconducting carbon nanotubes. We hypothesized that the polymers people were looking at were electron-rich, having a lot of electron density on them. If all the electron-rich polymers that have been looked at so far are selective for semiconducting carbon nanotubes, what would happen if we took an electron-poor conjugated polymer and looked at its interactions with carbon nanotubes?”
The answer became the cover story of Chemistry – A European Journal, where Adronov’s group showed that these electron-poor polymers have a tendency to disperse metallic nanotubes, leaving behind mixtures of semiconducting nanotubes. This approach could lay the foundation for the first industrially viable means of refining the raw material necessary to construct some of those long awaited devices, like foldable display screens or biological-electronic interfaces. “We believe we’re on the right track and we’re working to improve these polymers by making them more and more electron-poor, which is not easy to do,” says Adronov. “Fortunately, we are a synthetic group that likes the challenge of making something that’s difficult.”
Adronov adds that part of his group’s incentive is knowing that other researchers are exploring some of the same ideas about carbon nanotubes. Fierce international competition in this area requires his group to constantly monitor the work of others and continually advance innovative ideas. Keeping up with the competition also means that his laboratory must maintain cutting-edge equipment, such as recent upgrades to a fluorescence spectrometer as well as a laser used for Raman spectroscopy, both thanks to NSERC. Adronov also points to the ready access they have had to the Canada Centre for Electron Microscopy, located on the McMaster campus. “We use it routinely to analyze our material,” he says. “There’s no better place to do microscopy on nanomaterials.”