Experimental characterization of the growth dynamics during capillarity-driven droplet generation

Sarma, Bhaskarjyoti; Shahapure, Vijay; Dalal, Amaresh; Basu, Debabrata

doi:10.1103/physreve.100.013106

Cited by 4 publications

(8 citation statements)

References 59 publications

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“…In this context, droplet impact 12,13 and subsequent capturing by a fiber 14,15 have relevance in industrial processes like fog harvesting. Further, drop actuation on fiber, aided by gravity, i.e., drops flowing down a vertical fiber, 16 sliding or rolling on fiber, 17,18 or mechanisms of drop movement in fiber networks, 1 capillary driven drop propulsion in the absence of gravitational force, 19 and effect of airflow direction on drop movement due to varied fiber orientations 20 have been reported earlier. Gilet et al 17 reported that the sliding motion of a drop on a vertical fiber is governed by gravity and viscous forces for a droplet residing at the junctions of fiber networks.…”

Section: ■ Introductionmentioning

confidence: 78%

“…The shear resistance force, i.e., the friction due to shear stress is modeled as F normals = 2 π r normalc μ v ln y b where μ is the droplet viscosity, v is the droplet instantaneous velocity, y is the normal distance from the axis of the wire to the droplet tip, and b is the wire radius. The theoretically computed hysteresis and shear resistance forces for different droplet volumes are plotted as a function of droplet position in Figure b and c, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In this case, the critical size beyond which droplets crossed the junction is a function of the Bond number defined as the ratio between the droplet weight and capillary force exerted by the horizontal fiber. However, for droplets crossing a network of inclined fibers, the drop path depended on the slope and diameter of these fibers as reported by Weyer et al Similarly, Sarma et al provided a detailed theoretical analysis during droplet generation from a (vertical) wettable yarn, where three different regimes were demarcated based on the driving, gravitational force, and the resisting, capillary forces.…”

Section: Introductionmentioning

confidence: 87%

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Magnetic-Field Mediated Active Propulsion of Ferrofluid Droplets on a Wire

2023

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Droplet actuation on wires or fibers is highly relevant to digital microfluidics applications. Several different passive or active actuation mechanisms have been studied, including capillary pressure, thermal gradient, tilting, acoustics, and electrowetting, to name a few. However, the lack of precise control and accurate droplet positioning during its actuation on a wire limits the use of earlier methods. On the other hand, using a nonuniform magnetic field to actuate a droplet on a micrometer-size wire helps overcome the above limitations. In this context, we elucidate the motion of microliter-size ferrofluid droplets, smaller than the capillary length, in the presence of a permanent magnet using a simple yet robust experimental setup, wherein the clamshell shape droplets hang on a wire at a predetermined distance from the magnet. Beyond a critical volume, the droplet starts moving toward the magnet while exhibiting shape evolution continuously. Using a high-speed videography technique, we uncover the intricate relationship between the magnetowetting, favoring continuous shape evolution of droplets of different sizes, and their actuation dynamics (velocity) on a wire, which has scarcely been explored. The most significant contribution of this study is the detailed evaluation of the shape factor (k), relating the shape evolution of the droplet to its velocity through the contact angle hysteresis force. A theoretical framework has also been proposed, comprising different forces in action, which is found to set forth a good match with the experimental results. The results from this study are expected to open up new avenues in digital microfluidics, specifically in drug delivery, ferrobotics, and droplet logic gates, to name a few.

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Section: ■ Introductionmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 87%

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Magnetic-Field Mediated Active Propulsion of Ferrofluid Droplets on a Wire

2023

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“…The axial alignment of CNTs by capillary-driven self-assembly − was designed as shown schematically in Figure a. A two-step approach was used, where a commercial cotton fabric was immersed into an aqueous suspension of CNTs, followed by drying the soaked cotton fabric.…”

Section: Resultsmentioning

confidence: 99%

Axial Alignment of Carbon Nanotubes on Fibers To Enable Highly Conductive Fabrics for Electromagnetic Interference Shielding

Lan

Guo

et al. 2020

ACS Appl. Mater. Interfaces

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Conductive coatings show great promise for next-generation electromagnetic interference (EMI) shielding challenges on textile; however, their stringent requirements for electrical conductivity are difficult to meet by conventional approaches of increasing the loading and homogeneity of conductive nanofillers. Here, the axial alignment of carbon nanotubes (CNTs) on fibers that were obtained by spontaneous capillary-driven self-assembly is shown on commercial cotton fabrics, and its great potential for EMI shielding is demonstrated. The aligned CNTs structurally optimize the conductive network on fabrics and yield an 81-fold increase in electrical conductivity per unit of CNT, compared with the disordered CNT microstructure. The high-efficiency electrical conductivity allows a several-micron-thick coating on insulating fabrics to endow an EMI shielding effectiveness of 21.5 dB in the X band and 20.8 dB in the Ku band, which meets the standard shielding requirement in commercial applications. It is among the minimum reported thicknesses for conductive nanocomposite coatings to date. Moreover, the coated fabrics with aligned CNTs possess a desirable stability upon bending, scratching, stripping, and even washing, which is attributed to the dense CNT packing in the aligned microarchitecture. This work presents the anisotropic structure on large areas by self-assembly, offering new opportunities for next-generation portable and wearable electronic devices.

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“…133,134 Beyond a critical strength of the applied field, the droplet undergoes a bifurcation process preceded by the formation of a long neck, similar to the general dripping event from a non-wettable/wettable nozzle. 135,136 Studies have shown that in both the gravity-superimposed (with the magnetic field and gravity in the same direction) and gravity-compensated dynamics (with the magnetic field and gravity in the opposite direction), double pinch-off events were seen and the variation in the neck radius of the FF droplet was similar in both cases. 133 However, the location of the pinch-off event in the necking regime is determined by the magnitude and the type of the external field.…”

Section: Effect Of Non-uniform Magnetic Fieldmentioning

confidence: 99%