Determination of reliable Lewis acid-base surface tension components of a solid in LW-AB approach

In the Lifshitz-van der Waals-Lewis acid-base (LW-AB) approach, the interaction between a solid and a liquid is described mathematically as the geometric mean of their surface tension components. The surface tension components of the solid γ_s^LW,γ_s⁺,and γ_s^- are determined by measurement of the contact angles for various liquids whose surface tension components γ_l^LW,γl+, and γ_l^- are known. One of the two AB surface tension components of a solid γ_s⁺,and γ_s^- is often calculated to have a negative square root. In the conventional LW-AB approach, it has been assumed to be zero, which leads to the inaccurate evaluation of not only the other surface tension component but also the total interfacial Gibbs energy. In this study, the equations expressing the relationship between solid surface tension components and liquid surface tension components were plotted for various contact angles. The plots showed that a large deviation could occur in the values of γ_s^LW, √γ_s⁺, and √ γ_s^-, depending on the type of apolar liquid. Also it was found that there could be combinations of three liquids allowing the meaningful non-negative values for √γ_s⁺ and √γ_s^-.