RETENTION OF LIQUID-DROPS BY SOLID-SURFACES

A spinning platter has been used to study retention of relatively nonvolatile liquid drops on solid surfaces. The liquids used were ethylene glycol, glycerol, and water. Solids consisted of a variety of polymers, as well as glass. All liquid-solid combinations showed a characteristic value of the ratio F R of critical force to contact area radius, at which the drop, as a whole, began to move. The values are in reasonable agreement with measured values of the critical advancing and receding contact angles, θa and θr. The elongation of the drop before it became detached was found to increase with the difference in the contact angles. Roughening a PMMA surface dramatically increased both the retention force and the critical elongation of a drop. © 1990.