ABSTRACT
During wetting processes a fluid interface moves along a solid surface which it contacts. This motion can occur only if flow arises near the contact line. A mechanism is proposed for the origin of such flow. Flow along the fluid interface near a solid-liquid-gas contact line is produced, for example, by the action of intermolecular forces on the liquid near the contact line. Whether flow is toward or away from the contact line depends both on the relative magnitude of liquid-liquid and liquid-solid intermolecular forces and on the size of the contact angle. A simple theoretical analysis correctly predicts that at an advancing contact line, i.e., one where liquid replaces gas in contact with the solid, the contact angle exceeds its equilibrium value and flow along the fluid interface is toward the contact line. Similar predictions are obtained for receding contact lines. The predicted variation of equilibrium contact angle for different liquids on a single solid is also consistent with experimental data.
