Perfectly hydrophobic surfaces with patterned nanoneedles of controllable features

In this Letter, we present a simple and reproducible method for generating polystyrene (PS) nanoneedle arrays by utilizing the trapping of inorganic silica particles at the polystyrene/air interface via capillary wetting of a thermoplastic polystyrene polymer and SF(6) reactive-ion etching. A monolayer of silica microspheres was directly formed and trapped on the smooth PS film, and subsequent wet etching with HF and reactive-ion etching with SF(6) left behind hexagonal arrays of protruding tips with tip diameters around 20 nm. The patterned PS surface possessed a well-defined nanoneedle array with the pattern density as high as 2.5 x 10(8)/cm(2) and exhibited advancing and receding water contact angles of 180 degrees. The surface showed no affinity for water as confirmed by a series of contact, compression, and release tests. Finally, the perfect hydrophobicity of the fabricated surface is explained in terms of its surface morphology and chemical composition.