Abstract
We report tip-multi-breaking (TMB) mode of droplet breakup in capillary microfluidic devices. This new mode appears in a region embraced by Cai = 0 and lg(Cai) = − 8.371(Ca0) −7.36 with Ca0 varying from 0.35 to 0.63 on the Cai – Ca0 phase diagram, Cai and Ca0 being the capillary numbers of inner and outer fluids, respectively. The mode is featured with a periodic, constant-speed thinning of the inner liquid tip and periodic formation of a sequence of droplets. The droplet number n in a sequence is determined by and increases with outer phase capillary number, and varies from two to over ten. The distribution of both pinch-off time and size of the droplets in a sequence is a geometric progression of common ratio that depends exclusively on and increases monotonically with the droplet number from its minimum value of 0.5 at n = 2 to its maximum value of 1 as n tends to infinity. These features can help identify the unique geometric morphology of droplet clusters and make them promising candidates for encryption and anti-fake identification.
Highlights
We report tip-multi-breaking (TMB) mode of droplet breakup in capillary microfluidic devices
The droplet number n in a sequence is determined by and increases with outer phase capillary number, and varies from two to over ten. The distribution of both pinch-off time and size of the droplets in a sequence is a geometric progression of common ratio that depends exclusively on and increases monotonically with the droplet number from its minimum value of 0.5 at n = 2 to its maximum value of 1 as n tends to infinity
In a capillary microfluidic device (Fig. 1(a)), three modes have previously been observed[25]: geometry-controlled mode where the dimensions of the focusing orifice control the pinch-off of droplets, dripping mode with which the inner fluid finger narrows because of viscous shear force from the outer fluid, and the resulting droplet sizes are somewhat smaller than the orifice dimension, and jetting mode where a long viscous jet forms and
Summary
We report tip-multi-breaking (TMB) mode of droplet breakup in capillary microfluidic devices. The mode is featured with a periodic, constant-speed thinning of the inner liquid tip and periodic formation of a sequence of droplets.
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