Electropumping of water in functionalized carbon nanotubes using rotating electric fields

The development of new methods for the effective pumping of water at the nanoscale is an important building block in the development of nanotechnologies due to the limitations of current approaches, such as electro-osmotic flow. In this paper we present the first nonequilbrium molecular dynamics results that demonstrate an effective net positive flow of water molecules within a functionalized carbon nanotube without the use of an effective pressure gradient. We have applied a spatially uniform rotating electric field that couples with the permanent dipole moment of the water molecules. Breaking the symmetry of the nanotube walls by asymmetrically functionalizing the carbon nanotube with carboxyl groups, we then take advantage of the coupling of spin angular momentum of the water molecules to their linear momentum to induce a positive net flow. Surprisingly our results show that a net flow can be achieved with only a small amount of functionalization. The net flow resulting from only a small amount of functionalization can be attributed to a combination of the strongly hydrophilic nature of the carboxyl group combined with the small diameter of the carbon nanotubes. These two factors mean that the symmetry between the upper and lower halves of the carbon nanotube is easily broken with a small number of carboxyl groups.