ABSTRACT
Adhesional Wetting. When 1cm2 of planar solid surface comes into contact with 1cm2 of planar liquid, the unit surface area of each phase disappears to form a unit area of the new solid-liquid interface. The work (Wa) involved in this process under isothermal condition is represented as follows:
Wa=γS/L−(γS+γL/V) (4)
where γS/L, γS, and γL/V are the interfacial free energies of solid-liquid, solid-vapour, and liquid-vapour boundaries, respectively. Immersional Wetting. Total immersion involves the exchange of the solid-liquid interface without changing the amount of the
liquid surface. Immersional work is given as follows:
Wi=γS/L−γS/V (5)
where γS/V is the surfacial free energy which is in equilibrium with vapor and can be approximated as follows:
γS/V≈γS (6)
Spreading Wetting. When a drop of liquid is spread on flat solid surface, for every unit area of solid surface that disappears, equivalent areas of liquid surface and solidliquid interface are formed. The work for this surface is:
WS=(γS/L+γL/V)−γS/V (7)
The aforementioned three wetting stages are illustrated in Fig. 8. When a drop of liquid is wetted on solid surface and the contact angle is θ, each surface energy is related as follows:
γS/V=γS/L+γL/V cos θ (8)
Fig. 8 Three stages involved in the complete wetting of a solid cube by a liquid: (A-B) adhesional wetting, (BC) immersional wetting, and (C-D) spreading wetting.
