Towards Optimization of Patterned Superhydrophobic Surfaces
Bharat Bhushan, Michael Nosonovsky, Yong C. Jung
Experimental and theoretical study of wetting properties of patterned Si surfaces with cylindrical flat-top pillars of various sizes and pitch distances is presented. The values of the contact angle (CA), contact angle hysteresis (CAH) and tilt angle (TA) are measured and compared with the theoretical values. Transition from the composite solid-liquid-air to homogeneous solid-liquid interface is investigated. It is found that the wetting behavior of a patterned hydrophobic surface depend upon a simple non-dimensional parameter, the spacing factor, equal to the pillar diameter divided by the pitch. The spacing factor controls the CA, CAH, and TA in the composite interface regime, as well as destabilization and transition to the homogeneous interface. We show that the assumption that the CAH is a consequence of the adhesion hysteresis leads to the theoretical values of the CAH, which are in a reasonably good agreement with the experimental values. By decreasing the spacing factor to the value Sf = 0.111, the values of CA = 170 , CAH = 5 , and TA = 5 are achieved. However, with further decreasing of the spacing factor, the composite interface destabilizes.