Apparatus for controlling the movement of a liquid on a nanostructured or microstructure surface

An apparatus comprising:

• a surface having a pattern of features, said surface including:
• a pattern of nanoposts or microposts capable of supporting a droplet of liquid over said surface and having an intra-pattern characteristic adapted to produce a controlled motion of said droplet in a predetermined direction along the surface, wherein:
• at least a portion of said pattern of nanoposts or microposts is configured to cause a contact angle of a leading edge of said droplet to be lower than a contact angle of a trailing edge of said droplet in said predetermined direction,
• either a spatial density of said nanoposts or microposts increases along said predetermined direction, or, said nanoposts or microposts have asymmetric shapes and form a sawtooth pattern along said predetermined direction, and
• said predetermined direction leads to a location on said substrate having a different portion of said nanostructures or microstructures with a highest spatial density of said nanostructures or microstructures.