ABSTRACT
Adsorption of liquid vapor on a solid tends to lower the surface tension of the solid and increase the contact angle. The surface tension decrement at equilibrium adsorption is the equilibrium spreading pressure, πe = γS — γSV, where γS is the solid surface tension in vacuum and γSV that in equilibrium with the saturated vapor of the liquid [Eq. (1.32)]. The πe is usually negligible when the contact angle is larger than about 10°, but becomes significant when the contact angle is smaller than about 10°. When the contact angle is zero, just enough vapor will adsorb on the solid such that πe = γS — γLV — γSL (Section 1.6.2).
