Centrifugal Detachment of Compound Droplets from Fibers

This article presents the first experimental-computational study on the centrifugal detachment of a compound droplet (e.g., a primary water droplet cloaked by an immiscible oil) from a fiber. The work was intended to establish a method for quantifying the force needed to detach compound droplets of different compositions from a fiber. More importantly, our study was aimed at improving the understanding of the interplay between interfacial and external forces acting on a compound droplet during forceful detachment. The experiments were conducted using DI water, for the primary droplet, and silicone or mineral oil, for the cloaking fluid. It was observed from the experiments that the silicone-oil-cloaked droplets behave differently from the mineral-oil-cloaked droplets. It was also observed that detachment force decreases with increasing the oil-to-water volume ratio. The simulations were performed using the Surface Evolver (SE) finite element code programmed for the complicated four-phase (air, water, oil, and solid) interfacial problem at hand. Our simulations revealed the evolution of the interfacial forces between the interacting phases under an increasing external body force on the droplet. The simulations also allowed us to define effective interfacial tensions and contact angles for detaching compound droplets, for the first time. Reasonable agreement was observed between the experimental measurements and computational results.