Background
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:
![](/graphics/28/image-thumb__28__image-block-image_auto_674e747c3d753f06eca1cf5f649e7a97/kruss-eq-spreading-pressure-by-work.f6d5dad1.png?version=1 1x, /graphics/28/image-thumb__28__image-block-image_auto_674e747c3d753f06eca1cf5f649e7a97/kruss-eq-spreading-pressure-by-work@2x.f6d5dad1.png?version=1 2x)
Equally, the spreading coefficient can be expressed as the difference between the surface tensions σ1 and σ2 and the interfacial tension σ1,2:
![](/graphics/27/image-thumb__27__image-block-image_auto_965d6c637ef1927519b441639739f579/kruss-eq-spreading-pressure-by-tension.c3b95b54.png?version=1 1x, /graphics/27/image-thumb__27__image-block-image_auto_965d6c637ef1927519b441639739f579/kruss-eq-spreading-pressure-by-tension@2x.c3b95b54.png?version=1 2x)
If the spreading coefficient is positive, the phase under consideration spreads; if it is negative, wetting is not complete.
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