Magnetic field driven actuation of sessile ferrofluid droplets in the presence of a time dependent magnetic field

Shyam, Sudip; Asfer, Mohammed; Mehta, Balkrishna; Mondal, Pranab Kumar; Almutairi, Zeyad

doi:10.1016/j.colsurfa.2019.124116

Cited by 27 publications

(9 citation statements)

References 29 publications

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“…Interested readers are referred to our recent articles where the preparation of the ferrofluid solution has been discussed (Shyam et al. 2020 a , c ; Shyam, Mondal & Mehta 2020 b , 2021). Figure 1 depicts the characterization of the prepared ferrofluid sample.…”

Section: Methodsmentioning

confidence: 99%

Magnetofluidic-based controlled droplet breakup: effect of non-uniform force field

2022

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We report the breakup dynamics of a magnetically active (ferrofluid) droplet in a T-shaped Lab on a Chip (LOC) device under the modulation of a non-uniform magnetic field. We adhere to high-speed imaging modalities for the experimental quantification of the droplet splitting phenomenon, while the underlying phenomenon is supported by the numerical results in a qualitative manner as well. On reaching the T-junction divergence, the droplet engulfs the intersection fully and eventually deforms into the dumbbell-shaped form, making its bulges move towards the branches of the junction. We observe that the asymmetric distribution of the magnetic force lines, acting over the T-junction divergence, induces an accelerating motion to the left of the moving bulge (since the magnet is placed adjacent to the left branch). We show that the non-uniform force field gradient allows the formation of a hump-like structure inside the left moving bulge, which triggers the onset of augmented convection in its flow field. We reveal that this augmented internal convection developed in the left moving volume/bulge, on becoming coupled to the various involved time scales of the flow field, leads to the asymmetric splitting of the droplet into two sister droplets. Our analysis establishes that, at the critical strength of the applied forcing, as realized by the critical magnetic Bond number, the flow time scale becomes minimum at the left branch of the channel, leading to the formation of larger sized sister droplets therein. Inferences of the present analysis, which demonstrates a plausible means of independently controlling the size of the sister droplet by manoeuvring the applied force field gradient, will provide a potential solution for rapid droplet splitting, which typically finds significant importance in point-of-care diagnostics.

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Section: Methodsmentioning

confidence: 99%

Magnetofluidic-based controlled droplet breakup: effect of non-uniform force field

2022

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“…Consequently, positive counterions amass within the electrical double layer (EDL) at the structural interface due to the effect of native Debye screening. Under the Debye‐Huckel limit, the voltage drop

Δ {normalV}_{1}

(external minus internal) across the native EDL is determined by the degree of ion adsorption [26–32]:

Δ {normalV}_{1} = - \frac{q_{0}}{C}

where q 0 denotes the fixed free surface charge density adsorbed at the surface of conducting drop, C = ε/λ D the EDL capacitance, ε the liquid permittivity,

λ_{normalD} = \sqrt{D ε / σ}

the Debye screening length, D the ion diffusivity at room temperature, and σ the medium electric conductivity.…”

Section: Methodsmentioning

confidence: 99%

Pumping of electrolyte with mobile liquid metal droplets driven by continuous electrowetting: A full‐scaled simulation study considering surface‐coupled electrocapillary two‐phase flow

Liu

Tao

et al. 2020

Electrophoresis

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With the excellent merits of both solid conductors and rheological fluids, liquid metal (LM) provides new opportunities to serve as flexible building blocks of miniaturized electronic and fluidic devices. The phenomenon of continuous electrowetting (CEW) has been long utilized for actuating LM contents in buffer medium, wherein an externally imposed voltage difference is responsible of manipulating the interfacial tension of deformable LM droplets. CEW effectively lowers the surface tension at the LM/electrolyte interface by driving bipolar counterions to the surface of conducting droplet. Since surface tension coefficient relies sensitively on the local voltage drop across the induced double layer, an electric‐analogy Marangoni effect occurs even under a rather weak electric field in the presence of a surface gradient of the interfacial tension. CEW of LM routinely induces unidirectional pumping of electrolyte in the direction of applied electric field, with LM droplet translating oppositely within the device channel. Although this subject has received great attention from the microfluidic society in the past decade, previous reports concerned either the individual delivery of the suspension medium or the transport of LM droplet. Starting from this point, we offer herein a fully coupled physical description of two‐phase flow dynamics occurring in CEW. The proposed simulation model successfully incorporates the synergy of the interfacial electrokinetic momentum transfer, surface tension on a curved surface, contact angle at the three‐phase contact line as well as the gravity force density. The spatial‐temporal motion of the contact interface is traced instantly with a moving mesh approach. By direct numerical simulation, the importance of the direct‐current bias, additional alternating‐current forcing, droplet size, initial ion adsorption in the process of CEW is addressed. Additionally, it is discovered that increasing the number of LM droplet is more cost‐effective than enhancing the volume of a single drop in terms of achieving an improvement of the resulted electrocapillary pump performance, while the translational speed of the discrete droplet carrier does not make an observable change in response to a variation in the drop number. These results prove invaluable in terms of an elaborate design of smart on‐chip electrokinetic frameworks embedding flexible LM contents in modern micro‐total‐analytical systems.

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“…For the sake of conciseness in the presentation, we do not discuss here the remaining steps. The interested readers may refer to the recent work from our group for the detailed discussion of the involved stages of this process (Shyam et al, 2020a(Shyam et al, , 2020b. Figure 1(a) shows the magnetization curve of the prepared ferrofluid solution.…”

Section: Fluid Characterization and Substrate Preparationmentioning

confidence: 99%

“…The nanoparticles are usually stabilized by the surfactants such that they exhibit continuum behaviour in the presence of a strong magnetic field. Due to the superparamagnetic nature of the nanoparticles, this typical fluid has attracted significant attention from the scientific community because of its promising potential in the area of magnetofluidic based applications (Ganguly, Sen & Puri 2004;Afkhami et al 2008Afkhami et al , 2010Mahendran & Philip 2012;Rowghanian, Meinhart & Campàs 2016;Qiu et al 2018;Vieu & Walter 2018;Shyam et al 2019Shyam et al , 2020aShyam, Mondal & Mehta 2020b). More precisely, the rapid response of the nanoparticles to the magnetic field offers tremendous flexibility in stirring/mixing related applications in lab-on-a-chip devices/systems (Wang et al 2008;Tsai et al 2009;Zhu & Nguyen 2012;Kitenbergs et al 2015;Hejazian, Phan & Nguyen 2016;Nouri, Zabihi-Hesari & Passandideh-Fard 2017).…”

Section: Introductionmentioning

confidence: 99%

Magnetofluidic mixing of a ferrofluid droplet under the influence of a time-dependent external field

2021

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Magnetic field driven actuation of sessile ferrofluid droplets in the presence of a time dependent magnetic field

Cited by 27 publications

References 29 publications

Magnetofluidic-based controlled droplet breakup: effect of non-uniform force field

Magnetofluidic-based controlled droplet breakup: effect of non-uniform force field

Pumping of electrolyte with mobile liquid metal droplets driven by continuous electrowetting: A full‐scaled simulation study considering surface‐coupled electrocapillary two‐phase flow

Magnetofluidic mixing of a ferrofluid droplet under the influence of a time-dependent external field

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