ABSTRACT
Contact angle measurement, fi rst described by Thomas Young in 1805, remains at present the most accurate method for determining the interaction energy between a liquid (L) and a solid (S), at the minimum equilibrium distance o between S and L. The cosine of the contact angle θ (measured through the drop, at the tangent to the drop, starting at the triple point solid-liquid-air; (see Fig. XII-1) is a measure of the resultant of the energy of cohesion of the liquid, in the guise of γL and the energy of adhesion between liquid and solid, expressed as ΔGSL; see eq. [IV-11] (see also Fig. IV-1 and de Gennes, 1985). Thus the left-hand side of eq. [IV-11] shows the part of the free energy of cohesion of the liquid, which is equal to the free energy of adhesion between the liquid and the solid, shown on the right-hand side.
