= Complete wetting
A liquid spreads macroscopically over a solid with zero macroscopic equilibrium <contact angle>. In the simple interfacial-energy model the threshold is $\gamma_{SV}-\gamma_{SL}=\gamma_{LV}$, or zero <spreading coefficient>; positive coefficient favors a spreading film. Extrapolating a concentration-dependent liquid-vapour <surface tension> to this threshold assumes the other interfacial energies remain fixed and no intervening adsorption or micellization behavior changes the trend.
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