Experiment of Johnson and Dettre

In practically every case we have discussed up to now, the solid surface was assumed to be ideal, that is to say, smooth and chemically homogeneous. The contact angle 6e oi a, drop on such a solid is given by the now familiar Young relation, which is reproduced here  

FIGURE 9.1. Static contact angles (advancing and receding) of water drops placed on wax surfaces as functions of the roughness of the substrate. The horizontal scale is qualitative changes in roughness are achieved by successive bakes (reproduced from ref. 1). 

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The fundamental experiment of Johnson and Dettre (Figure 9.1) indicates that a single scenario is not necessarily sufficient to explain how roughness influences the wetting properties of a solid. The data suggests two... 

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