Measurement of Lateral Adhesion Forces at the Interface Between a Liquid Drop and a Substrate

The relation between drop radius, r, the force to move the three phase contact line and the advancing and receding contact angles is studied. To keep the line energy (energy per 2pr, also named line tension) independent of r, the modified Young equation predicts that the advancing and receding contact angles change considerably with r. As shown by many investigators, in reality this change is negligibly. We quantify recent evidences showing that the line energy is a function of the Laplace pressure and show that this way the modified Young equation is correct and still the advancing and receding contact angles should hardly change with r. We survey new experiments using the newly developed Centrifugal Adhesion Balance (CAB) and show how they can further support the reconciliation of this apparent paradox.