Tailoring Anisotropic Wettability Using Micro-pillar Geometry

Anisotropic surfaces have great potential in important applications like microfluidic devices, lab-on-chip systems, micro-reactors, coatings and printings. Anisotropic wetting behavior on micro-pillars is of particular interest since micro-scale morphology on many natural anisotropic wetting surfaces are pillar-like structures. It is found that the micro-pillars show anisotropic wettability at Wenzel state and isotropic wettability at Cassie state. Increasing the micro-pillar height will lead to the result that anisotropic wettability switches to isotropic wettability. Increasing space ratio may amplify the anisotropy. The relationship between anisotropic wettability and wetting state is interpreted by a thermodynamic model. The anisotropic-isotropic wettability switch can be attributed to the wetting state transition due to the intruding height change. Our findings may improve the understanding of the anisotropic wetting behavior on micro-pillars and provide an easy way to tailor the anisotropic wettability by simply changing the micro-pillar geometry. (C) 2014 The Authors. Published by Elsevier B.V.