Magnetowetting dynamics of sessile ferrofluid droplets: a review

Deb, Rupresha; Sarma, Bhaskarjyoti; Dalal, Amaresh

doi:10.1039/d1sm01569a

Cited by 22 publications

(11 citation statements)

References 206 publications

(565 reference statements)

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“…Magnetic droplets undergo reversible or irreversible shape evolution when they are subjected to either a uniform or nonuniform magnetic field. 32 Notably, any typical shape evolution of a magnetic droplet, either in sessile or pendant state, can be characterized in terms of changes in the dynamic contact angle (both advancing (θ adv ) and receding (θ rec ) contact angles), wetting length (l d ), and droplet height (h d ). For a droplet-on-wire system, we have schematically depicted the aforementioned parameters in Figure 3b.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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: ■ Results and Discussionmentioning

confidence: 99%

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

2023

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“…), the surfactant properties, and the temperature and initial concentration. The results discuss the wetting, interfacial dynamics, surface stress, and hydrodynamic instabilities of drying ferrofluid systems [50].…”

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confidence: 95%

Drying of bio-colloidal sessile droplets: Advances, applications, and perspectives

Pal

Gope

Sengupta

2023

Advances in Colloid and Interface Science

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“…Ferrofluids, which consist of ferromagnetic colloids in solution, 1,2 have found industrial applications such as loudspeaker cooling, sealing rotating shafts, and high-speed printing. 3 They have been used in areas as diverse as sculpture, 4 self assembly, 5 medicine, 3 and even digital logic.…”

Section: Introductionmentioning

confidence: 99%