(64d) An Examination of Sessile and Pendant Drop Retention Forces

Drop adhesion force, the force required to slide a drop along a surface, is an important parameter used in fluid dynamics, agriculture, and environmental science. The tilt plate method is the most conventional way to study drop lateral adhesion forces. However, there are two obvious limitations associated with this method. Firstly, the range of forces that can be applied to the drop are limited by the experimental setup, as the maximum force that can be applied is the drop's weight. Secondly, the tilt stage experimental setup requires that both the normal and lateral (retention) forces, which are applied to the drop, change simultaneously. Accordingly, our group has assembled the first model of a novel instrument that negates these limitations. This instrument, the Centrifugal Adhesion Balance (CAB), allows drops to slide on a surface by the application of centrifugal force. Thus, the drops are no longer limited in terms of the range of forces that can be applied. Additionally, because of the experimental equipment, the normal and lateral force components can be decoupled, effectively eliminating the second limitation. In these experiments, our group has compared truly sessile and truly pendant drop retention forces. We have also examined the relationship between drop resting time and drop retention force. Effectively, we are interested in not only determining the quantitative values for the retention forces but also determining the effect of surface deformation and the parameters that cause surface deformation on these forces.