Investigation and application of an ultrahydrophobic hybrid-structured surface with anti-sticking character

Hybrid-structured surfaces consisting of microgrooves and nanocrystals have been modified with a self-assembled monolayer (CF3(CF)(7)CH2CH2SiCl3) via low-cost, mass-production and highly integrated nano/microfabrication. The microgrooves decorated with nanocrystals were patterned and fabricated on a silicon substrate to yield an ultrahydrophobic surface with an anti-sticking property. The nanocrystals were etched by means of oxidation of the silicon surface. Contours of nanostructured surfaces were inspected with a SEM and an AFM; the surface roughness and level of hydrophobicity depended on the duration of etching. Comparison of contact angles for microliter droplets on those designed surfaces showed that the hydrophobicity of the solid surfaces became amplified with nanocrystals and accurately modulated with a pattern density (f(1)), ranging from 112 degrees to 173.1 degrees, to generate a much increased gradient of Gibbs surface energy that served to transport the droplet. To characterize the anti-sticking capability of those hybrid-structured surfaces in quantity, we measured the heights and frequencies of rebounding droplets on those test surfaces with varied roughnesses. Similar to the interfacial characteristics of a lotus leaf, our designed surfaces feature superior aqueous repellence, little hysteresis and slight adhesion, such that droplets hence roll off effortlessly and bounce off repeatedly.