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This article presents the analysis for determining surface free energy uncertainty by the Owens–Wendt method (also known as the Kaelble–Owens–Wendt method). There are a lot of factors which have a substantial influence on the correctness of the contact angle measuring process. If a full measurement result is to be obtained, assessment of the result reliability is needed. In the case of distilled water wetting angle measurements, dispersion of the results may be assumed as a normal dispersion (according to the χ2 test). In contrast, in the case of diiodomethane wetting angle measurements, dispersion of results cannot be treated as normal dispersion. This may demonstrate that if numerous factors are analysed, usually there is one dominant factor—in this case, a drop of liquid. The uncertainty resulting from different quantities of constants, given in the literature, is of great importance in the standard uncertainty overall error, both for the total surface energy and for its polar and dispersive components. Thus, it cannot be neglected at the examination reliability assessment.
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