Contact lines chemically heterogeneous surfaces

Gao and McCarthy showed experimentally that the contact angle of a drop is defined by the triple line and does not depend upon the roughness under the bulk of the drop. A similar result for chemically heterogeneous surfaces was obtained by Extrand. " ... 

Fig. 3.12 (a) Configuration and materials for the two chemically heterogeneous surfaces 1 and 2, (b) water contact angles at t=0 and after the contact lines advance across the material boundary... 

The same line of reasoning can be applied to a surface that is planar but chemically heterogeneous. We will now assume the surface to be made of two species (Figure 9.3), each characterized by its own contact angle 6i and... 

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