Capillary transport from barrel to clamshell droplets on conical fibers

Abstract

Droplets spontaneously move when they are placed at the tip of a cone surface. Using three dimensionally printed structures, we experimentally explore a large panel of configurations regarding the aperture angle of the cone. We evidence a change of the droplet geometry while moving along the conical fiber. This transition is a switch of configuration from barrel to clamshell shape. The consequence is a change in the droplet dynamics. We estimate the position of this geometrical transition and we propose two models to describe the motion of the barrel and the clamshell droplets. While both shapes are driven by capillary forces, the dissipation is dependent on the geometrical configuration. For barrel shape droplets the main dissipation appears to be in the liquid wedge. For clamshell shape droplets the dissipation occurs mainly in the liquid film close to the conical fiber.

Multiple droplets on a conical fiber: formation, motion, and droplet mergers

“…And lastly, a larger droplet has a greater difference in the advancing and receding contact lines resulting in a higher velocity. These relationships, though well established in the literature, 17,19,20,23,[28][29][30][31] are important for providing an intuitive understanding of the results presented.…”

“…Before discussing the case of multiple droplet migration we first present an intuitive description of the motion of an isolated droplet which has been studied extensively. 17,19,20,23,[28][29][30][31] Here we follow the essential ingredients of a model presented by Fournier et al 19 aplicable to length-scales where the droplet is much smaller than the capillary length, and the effect of gravity is negligible. In short, the motion is driven by the rate of change in capillary energy, which is dissipated by the liquid viscosity.…”

“…26,27 The motion of a single droplet on a slender conical structure has been studied and characterized extensively, with an excellent understanding of the driving forces and viscous dissipation in the droplet. 17,19,20,23,[28][29][30][31] Furthermore, previous works have examined the formation of multiple droplets via the Plateau-Rayleigh instability (PRI) of a film of liquid on a cylindrical fiber. 32,33 In addition, studies have examined wetting and coalescence of droplets on a fiber network with particular interest in droplet capture in textiles [34][35][36][37][38] However, there has been little work on the formation and interaction between multiple droplets as they traverse along a conical fiber beyond qualitative observations, 17,32,39 despite being prevalent in nature as illustrated in Fig.…”

Magnetowetting dynamics of sessile ferrofluid droplets: a review

“…Notably, alteration of the surface energies can be achieved by using either passive or active techniques as per the target application. 10–32 Passive techniques for manipulating the wetting behaviour of droplets primarily include topology modification, 10–13 a change in the chemical properties of the surface 14–16 or diluting the droplets with surfactants or nanoparticles. 17–19 By contrast, using external stimuli via a number of active manipulation strategies, the wetting behaviour of the sessile droplets can be modified.…”

Multiple droplets on a conical fiber: formation, motion, and droplet mergers

“…As the characteristic size of the droplet becomes larger than the capillary length, the droplet may then be either propelled [21][22][23][24] or stalled [25] by gravity, and motion depends on the orientation of the conical structure and motion can be induced in these systems by temperature gradients or coatings [26,27]. The motion of a single droplet on a slender conical structure has been studied and characterized extensively, with an excellent understanding of the driving forces and viscous dissipation in the droplet [17,19,23,[28][29][30][31][32]. Furthermore, previous works have examined the formation of multiple droplets via the Plateau-Rayleigh instability (PRI) of a film of liquid on a cylindrical fiber [33,34].…”