The researchers used multiwalled carbon nanotubes with diameters of about 50 nm and a mean length of around10 µm. They suspended the tubes in low-molecular-mass polyisobutylene (PIB) fluids at concentrations of 0.025% to 0.85% by mass.

The researchers studied the effects of shear stress on the suspensions using an optical shear cell. The sorting effect was most pronounced in the mid semidilute regime at shear rates of 5 to 15 s-1.

As well as having applications in processing nanotubes, the technique could provide an insight into the flow-induced anisotropy of rigid-rod polymers.

According to Erik Hobbie of NIST, 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.

The researchers reported their work in Physical Review Letters.