When carbon nanotubes are produced, they come in a mix of “chiralities” (or handedness), but the nanotubes need to be rich in one chirality if they are to be used in applications as diverse as drug delivery, biosensors, transistors and in high-performance electronics which is difficult to achieve.

However, to make such devices, the tubes need to be rich in one chirality. Researchers at the University of Oklahoma in the US now suggest that certain surfactants could effectively separate out bundles of nanotubes in which the carbon atoms are then all arranged in the same way.

A single-walled carbon nanotube (SWCNT) is a sheet of carbon just one atom thick rolled up into a tube that has a diameter of about 1 nm with the atoms in the sheet arranged in a hexagonal lattice. The relative orientation of the lattice to the axis of the tube, or its chirality, determines whether the tube is a metal or a semiconductor and so what type of electronic properties it has.

Researchers say using molecular dynamics simulations that surfactants, such as sodium cholate and flavin mononucleotide (FMN) could efficiently separate out SWCNTs based on diameter and chirality. They suggest that increasing the repulsion between individual nanotubes yields more stable dispersions of single-chiral tubes.

The researchers say that the aqueous surfactant aggregates should be rigid and that the hydrophilic parts of the surfactants (the parts that like to remain in contact with water) should be as far away as possible from the nanotubes. Such a recipe should produce nanotubes of the desired diameter and chirality.