Process ‘problem’ probed

(NIST) and university researchers report a significant step toward solving the nanotube "problem", namely the challenge of overcoming processing obstacles so that the properties of the cylindrical structures can be exploited in new polymer composite materials of exceptional strength.

Described in the current issue of Physical Review Letters, their analysis reveals that, during mixing, carbon nanotubes suspended in viscous fluids can be encouraged to sort themselves by length. Achieving uniform sizes of nanotubes is one of several keys to producing affordable, high-quality polymer nanocomposites.

The team found that, under common processing conditions, shorter carbon nanotubes will flow toward the walls of mixing equipment, while the longer tubes tend to congregate in the interior.

Better understanding of factors that promote this self-sorting will point the way to process adjustments and devices that achieve desired arrangements of nanotubes during bulk manufacturing of polymer nanocomposites, says NIST's Erik Hobbie, leader of the collaboration, which included scientists from the University of Kentucky and Michigan Technical University.