LINE TENSION EFFECT ON CONTACT ANGLES - AXISYMMETRICAL AND CYLINDRICAL SYSTEMS WITH ROUGH OR HETEROGENEOUS SOLID-SURFACES

Equations for the apparent, intrinsic, and actual contact angles are p resented, which account for the effect of line tension in axisymmetric and two-dimensional (cylindrical) systems with rough or chemically he terogeneous solid surfaces. The central point in the present theory is the realization that line tension cannot be considered constant. The dependence of line tension on the geometry of the system may be extrem ely complicated. Therefore, the simplifying assumption that line tensi on is a function only of the position of the contact line is made. The physical meaning of this assumption is that line tension affects only the contact angle and not the shape of the liquid-fluid interface. In two-dimensional (cylindrical) systems, this geometrical dependence is responsible for the existence of a line tension effect, in contrast t o the currently held view. The implications of the theory are discusse d in terms of the relationships between the Young's, actual, and intri nsic contact angles. (C) 1998 Elsevier Science B.V.