Cassie’s equation

Here, r = 470 nm and R = 500 nm. We thus obtain the value of /2 = 0.8013. The 0 value, for the flat silica surface without micro-pores, after modification, is experimentally about 114°. So the CA for our modified micro-porous sample can be estimated to be about 152.5° by Cassie s equation, equation (2), which is in good agreement with our result. 

If a heterogeneous surface is treated as consisting of two domains, Cassie s equation can be applied as follows (2) ... 

Wetting on rough or chemically patterned surfaces has also been studied for a long time. Two well-known equations, the Wenzel s equation [11] and the Cassie s equation [12] are introduced to characterize the macroscopic apparent contact angle in terms of surface roughness and inhomogeneity (see Equations (4.6) and (4.7) in Section 4.3). There have been many works on the derivation and validity of these two equations [10,13-17], despite some controversies on their correctness [18-22]. In particular, they cannot describe the contact angle hysteresis and cannot explain some of the experimental observations [18,23]. Various modifications or variations of these two equations are proposed and studied [10,20,24-26]. 

FIG. 25 Apparent contact angles for 60PlM-0Sn solder spreading on Cu with stainless steel heterogeneities of area fraction s. Solid lines are Cassie s equation. (From Ref. 17.)... 

Figure 15 Surface characterization of 2SiPAS films by static contact angle (o) surface free-energy ( ) BATS content calculated by Cassie s equation (in surface).

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