Boron nitride nanotube films grown from boron ink painting

The growth of nanotube films can have important applications in building nanoscale functional devices or solving interfacial and heat problems. We report that high-density boron nitride nanotube (BNNT) films with any desired pattern can be grown on complicated surfaces using a boron (B) ink process. The special B ink, a mixture of nanosized B particles, metal nitrate and ethanol, is first painted, sprayed or inkjet printed at the desired location with required pattern, and then the ink layer is annealed in a nitrogen-containing atmosphere to form BNNT film. This is the first method capable of growing BNNTs on complex non-flat surfaces, which greatly broadens the potential application of BNNTs. For example, it is demonstrated here that a BNNT coated steel mesh can separate water and oil on a microlitre scale; a needle given an internal BNNT coating could greatly enhance microfluidic transport; and a coated screw could be used to minimize wear at the interface.