  The growth of nanotube films on various substrates and surfaces is vital for
applications in nanoscale functional devices. We report a simple and versatile
boron (B) ink painting method that enables high-density boron nitride nanotube
(BNNT) films with any desired pattern to be grown on, and firmly attached to,
different surfaces. In the method, special B ink is first painted, sprayed or
inkjet printed at desired location with required pattern, and then the ink
layer is annealed in a nitrogen-containing atmosphere to form BNNT film. The B
ink is a liquid mixture of ball-milled B particles, metal nitrate and ethanol.
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 that a BNNT coated steel mesh can separate water and oil on a
microliter 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.
