On the validity of force balance models for predicting gravity-induced detachment of pendant drops and bubbles

Abstract

We show that it is fundamentally inaccurate to apply force-balance models to predict the gravity/buoyancy induced detachment of quasi-steadily growing pendant droplets/bubbles. We solve the governing Young-Laplace (Y-L) equation to clarify that all forces acting on a droplet/bubble always sum up to zero, even prior to or beyond the well-accepted critical volume of detachment. Accordingly, the typical force balance models reported in the literature do not hold any physical justification and are merely a curve fit to the experimental trends. We clarify that the physical constraints imposed by the contact line conditions and the surface geometry are instead responsible for detachment.