Surface Evolver Simulation of Droplet Wetting Morphologies on Fiber Without Gravity

Abstract

Droplet wetting phenomenon is encountered in many engineering applications. Three wetting morphologies, namely, barrel, clamshell, and liquid bridge, are investigated by the finite element method, Surface Evolver (SE) simulations. The barrel shape shrinks gradually as contact angle increases. In the shrinkage process, the dimensionless wetting length reduces, and maximum diameter increases. As the increase of the contact angle, the gas–liquid contact line of clamshell droplets bends and contracts inward gradually. The geometry parameters are extracted from the results from simulations. In addition, the critical spacing of liquid bridge rupture is determined. The critical spacing increases rapidly with the expanding of liquid bridge volume. The liquid bridge volume has a significant effect on critical spacing.

Experimental verification of the additivity between the barrel droplet's drag force and the fiber number

“…The droplet shape transforms from barrel shape to clamshell shape and the droplet transport speed increases, which further validates Carroll's conclusion. Xu 12 and Chou 13 used the Surface Evolver to simulate the shape of droplets on a cylindrical surface and studied the influence of the contact angle on the droplet volume. Lu 14 also used the Surface Evolver software to simulate the morphological transition process of droplets with different radii and wetting characteristics on a cylinder.…”

Static wetting of a barrel-shaped droplet on a soft-layer-coated fiber

“…The wetting of droplets on fibers is ubiquitous in both industrial and natural phenomena, and examples range from the modulation of the mechanical properties of spider silk, 33 to the droplet transport on spines of cacti, 34 to water collection by fog nets. Compared to a planar surface, the slender geometry of fibers modifies the droplet shape, 27,31 and could induce directional motion of droplets. 26,[35][36][37] When it comes to droplet wetting on soft fibers, most studies have focused on the bending and buckling of flexible fibers which result in, for instance, the winding around a droplet, 38 the coiling inside a droplet 39 or the modification of droplet morphology by multiple fibers.…”

“…effects of gravity are neglected), the shape of a droplet on a fiber is far more complex. Extensive studies in the literature 31,41,42 have shown that stable droplets can appear in an axisymmetric barrel-shape or a non-axisymmetric clamshell shape. For small equilibrium contact angles y and large droplet sizes relative to the fiber radius, axisymmetric barrelshaped droplets tend to be more stable.…”

“…When the droplet size (V 1/3 , here V is the droplet volume) is smaller than the fiber radius, barrel-shaped droplets exist only for y t 101. 31 In this study, we investigate the axisymmetric deformation of a soft solid layer coated on a rigid cylindrical fiber when a barrel-shaped droplet is embracing it. Previous studies of elastic deformation by wetting often assume that y = 901, and thus the solid surface tension of the soft-solid/liquid interface g sg is the same as that of the soft-solid/gas interface g sl .…”

“…1,2 The shape of deformation has been explored extensively in the last few decades; however, those studies have mainly focussed on situations of a droplet on a planar substrate. 1–25 Although there have been numerous studies of droplets on rigid fibers, 26–31 wetting on a rigid fiber coated with a soft layer has been far less investigated. 32 How this geometry modifies the deformation of the coated elastic layer remains unclear, which is the focus of this study.…”