Researchers in the US have discovered a novel method of improving the solubility of carbon nanotubes, which could lead to new types of packaging with improved functionality.
Somenath Mitra, professor of chemistry and environmental sciences and Zafar Iqbal, also a professor of chemistry and environmental sciences at the New Jersey Institute of Technology (NJIT), found that by heating nanotubes in a closed vessel microwave oven, they can be chemically modified without damaging their essential structure.
"A carbon nanotube is just carbon," said Mitra. "The surprise for us is that it's difficult to make nanotubes react with anything. They are like diamonds - very, very inert. They don't react and they don't dissolve in water. But, if you can change their chemical characteristics as we have done using our method, we see them transform right before our eyes."
Once the tiny, microscopic tubes are chemically altered, they become soluble in common solvents like water and alcohol, and new kinds of films or coatings can be produced. The functionalised nanotubes become more useful than the pristine ones because the functionalised groups can be tailored for specific applications.
In the pharmaceutical arena, there is a growing demand for improved packaging materials that protect compounds from environmental assaults as new medicines - often now biological proteins such as antibodies - become more complex and less stable.
For these molecules, conventional pharmaceutical packaging - which is already fairly sophisticated with regards to strength, clarity, durability, moisture protection, weight and processability - may not be enough.
For example, potential applications for the modified nanotubes could include the attachment of oxygen-scavenging compounds that inhibit the breakdown of the active ingredient in drugs, or indeed active sensor compounds that give a visual warning when a pack is exposed to biological, chemical or other environmental factors, or if the drug it contains is broken down. Similar 'active packaging' approaches are being developed using polymers.
And away from the external packaging arena, the discovery could also facilitate research into other applications of carbon nanotubes, including filter applications for pharmaceutical processing and using them as vehicles for drug delivery.
For their part, Mitra and Iqbal also believe that their discovery could lead to cheaper and more environmentally friendly production.
"We understand ourselves to be the first in the world to have discovered this method," said Mitra. "The beauty is that our method is green and clean. We use no toxic material and reduce the reaction times from hours - on occasion even days - to three minutes."
Iqbal noted that the method costs much less than others currently used. "Plus, the solubility of our carbon nanotubes are several times higher than any other researcher has yet reported in this short amount of time."
Solubility is the most essential characteristic of carbon nanotubes since researchers must be able to dissolve them to see how they work.
"Nanotubes are opening new vistas for products and design," said Mitra.
The pair, aided by doctoral student Yubing Wang, have written "Microwave-Induced, Green and Rapid Chemical Functionalisation of Single-Walled Carbon Nanotubes," to be published in a forthcoming issue of the journal Carbon.