= Spreading coefficient
{title2=$S=\gamma_{SV}-\gamma_{SL}-\gamma_{LV}$}
The excess interfacial <free energy> released per newly wetted area when a liquid film replaces a solid-vapour interface is the displayed coefficient. Positive $S$ favors macroscopic spreading in the ideal equilibrium surface-energy model, whereas negative $S$ permits a finite <contact angle> obeying <Young's equation>. Surface preparation, chemical composition and adsorption can change all three interfacial energies.
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