STUDYING THE DROP RETENTION FORCE

The force, f, required to slide a drop on a surface is found to be a growing function of the time, t, the drop waited resting on the surface prior to the commencement of sliding. We demonstrate the existence of this phenomenon in different systems, which suggest that this phenomenon is general. The increase in the force, f, due to the resting time effect correlates well with the vertical component of the liquid-vapor surface tension, and we attribute this phenomenon to the corrugation of the surface by the drop due to this unsatisfied normal component of Young s equation. We show that this rested-time effect is similar for different drop sizes. The conventional tilt stage method could not be applied for a lot of studies due to the coupling of normal and lateral forces inherent in this method. Additionally the range of forces that can be applied with the tilt stage is limited between zero to the drop s weight. A novel instrument has been built that allows measurements of the lateral adhesion forces at a solid-liquid interface, in a way that is decoupled from the normal forces.