Accuracy of contact angle data

Generally, smooth surfaces are more easily obtained with monocrystals. The same average roughness Ra can be obtained by mechanical polishing of polycrystals but this operation often leads to an accidental roughness on this type 

At high temperatures or in an atmosphere with a low P02, oxide films are often eliminated by dissolution in the metal, by thermodynamic decomposition or by formation of volatile sub-oxides. Even in these conditions, oxygen can still affect wettability, for instance by adsorption at metal/oxide interfaces. This effect leads to contact angles lower than the nominal contact angle of the inert system. Some examples of these oxygen effects are given in Section 6.4. Therefore, when contact 

At present, when working with high-purity materials, smooth solid surfaces and low P02 atmospheres, the thermodynamic contact angle in a particular system can be determined at best within about five degrees. Roughness must be very low, particularly in non-wetting systems in order to obtain such an accuracy. The control of P02 is critical for oxidisable liquids and solids, specially at relatively low temperatures, and dynamic vacuum is often preferable to a static neutral gas atmosphere. 

When the optimal conditions are satisfied, i.e., a well-controlled atmosphere, a pure, homogeneous and smooth solid surface and an accurate measurement system, the Young contact angle and the liquid surface energy can be derived with an accuracy of 3 deg and 2% respectively allowing the work of adhesion (Wa = TlvO + cos0)) to be determined with an accuracy of about 10%. 

Bashforth, F. and Adams, J. C. (1883) An Attempt to Test Theory of Capillary Action, Cambridge University Press 

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