Coalescence of droplets on micro-structure patterned hydrophobic planar solid surfaces

Abstract

The motion and coalescence of sessile liquid droplets on patterned solid surfaces are investigated systematically in terms of the liquid and substrate surface properties. A patterned silicon surface is decorated with circular pillars. The fabrication of the substrate is carried out by following standard photolithography. A thin photoresist layer of AZ-9260 on the pillars makes the surface exhibit superhydrophobic properties. The pillars are obtained using a deep reactive-ion etching process. Due to the deposited material and the increment of surface roughness, the liquid wetting behavior varies dramatically. The wetting properties of deionized water droplets on the patterned surface are examined to improve the understanding of the coalescence process. The coalescence of droplets is realized using capillary force on one of the droplets sitting at the boundary of surfaces with and without micro-patterns.