Droplet migration on conical fibers

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

“…For droplets below the capillary length, motion is driven by the surface tension of the droplet to maximize contact with the fiber when the droplet wets the fiber. 11,[17][18][19][20] As the characteristic size of the droplet becomes larger than the capillary length, the droplet may either be propelled [21][22][23][24] or stalled 25 by gravity depending on the fiber orientation. Droplet motion can also 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. 17,19,20,23,[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.…”

“…outer diameter, World Precision Instruments). 19,28 The capillaries are locally heated and pulled with a constant force using a micropipette puller (Narishige PN-30). The resulting shape is a smoothly tapering conical glass fiber with the base of the fiber being the diameter of the original capillary tube (1 mm), and the tip being tens of microns in diameter.…”

“…The resulting droplets are transferred by bringing one of the droplets into contact with the fiber. 19 This method allows for the precise placement of individual droplets along the fiber. A droplet can be placed at the tip of the fiber and allowed to completely move to the base of the fiber to deposit a thin film to act as a lubrication layer for subsequent droplets.…”

“…A large droplet moves more quickly toward the base of the fiber compared to a smaller droplet. 19 We place a smaller droplet closer to the base of the fiber, and a larger droplet is placed closer to the tip allowing for the larger droplet to catch up to the smaller droplet, coalesce, and merge.…”