Figure 4
The effect of the area-fraction (f) on the wetting transition. (a) Top-view SEM images of the pPFDA-coated VA-CNT micropillar samples (height, H = 90 µm and center-to-center spacing, S = 100 μm) with area-fractions (f) of 0.12, 0.19, 0.28, and 0.38 (left to right) for micropillar radius (r) of 20 µm, 25 µm, 30 µm, and 35 µm respectively. The scale bar is 100 µm. (b) Plots showing the variation in the contact angle, θ (left panel), Laplace pressure, PL (middle panel) and force per unit length, FPL (right panel) during the evaporation of a 4 μL water droplet. The calculated FPL values are much lower than the critical FPL value of 0.090 N/m for all the area-fractions (f) further verifying the local force balance model in prediction of wetting-transition.
