Fig. 4.
(A) Experimental observation of monostable (open dots) or bistable (solid dots) Cassie states. The phase space decouples surface chemistry (expressed by θr) from texture (expressed by the surface fraction f). Silicon posts are either square (squares) or circular (circles), with height h =100 μm and side (or diameter) a = 100 μm. The surface fraction f is varied by changing the post separation b. The receding angle is tuned by changing the treatment applied to the material, and averaged over five measurements; error bars indicate the SD of data. The dashed black line is Eq. 1, found to separate quite nicely the green region of monostability from the regions of bistability. The red dashed line is drawn by replacing in Eq. 1 the receding angle by the equilibrium contact angle. Background colors correspond to the respective energy diagrams drawn in B.