Adding carbon nanotubes to plastics and other polymers has potential to make automobile and airplane bodies stronger and lighter, and textiles more tear-resistant. And because of their electrical properties, carbon nanotubes also may be used to embed sensors in clothing for military and medical applications. By one estimate, the carbon nanotube market valued at approximately $12 million in 2002 could grow to $700 million by 2005.
One problem, however, is the nanotubes tend to clump together in certain applications. Just as an oil and water salad dressing must be shaken thoroughly to mix well, carbon nanotube formulations must be thoroughly blended to perform their best.
In a set of experiments reported in the Jan. 30 issue of Physical Review Letters, researchers at the National Institute of Standards and Technology (NIST) have started to quantify both the problem and the solution. The scientists used a microscope and an "optical flow cell" to measure the force needed to mix different concentrations of nanotubes. Their findings suggest that flow conditions often encountered in the processing of carbon nanotube suspensions can actually have the opposite effect, leading to demixing. The effect is related directly to the long fiber-like structure of the nanotubes. Although this work only sets the stage for resolving what will be an important technological issue, the findings give researchers insight into how to process nanotubes more efficiently.