The spreading coefficient or parameter is a measure of the tendency of a liquid phase to spread (complete wetting) on a second, liquid or solid phase.
The spreading coefficient S is the difference between the work of adhesion W1,2 between the phases and the work of cohesion W1,1 of the phase under consideration:
Equally, the spreading coefficient can be expressed as the difference between the surface tensions σ1 and σ2 and the interfacial tension σ1,2:
If the spreading coefficient is positive, the phase under consideration spreads; if it is negative, wetting is not complete.
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