Ferrofluid droplet breakup process and neck evolution under steady and pulse-width modulated magnetic fields

Bijarchi, Mohamad Ali; Favakeh, Amirhossein; Mohammadi, Kaivan; Akbari, Ali

doi:10.1016/j.molliq.2021.117536

Cited by 16 publications

(6 citation statements)

References 41 publications

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“…Ferrofluid is a stabilized suspension of magnetic iron oxide nanoparticles in a water or oil media and responds to external magnetic stimuli. − Today, ferrofluid is extensively used in microfluidic systems thanks to the controllability it demonstrates with an external magnetic field. ,− Researchers have widely inspected the dynamic and manipulation of naked ferrofluid droplets under external magnetic fields, − while utilizing ferrofluid liquid marbles (FLMs) in digital microfluidic systems has not been studied widely.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Theoretical Investigation on the Dynamic Response of Ferrofluid Liquid Marbles to Steady and Pulsating Magnetic Fields

2023

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Liquid marbles are droplets enwrapped by a layer of hydrophobic micro/nanoparticles. Due to the isolation of fluid from its environment, reduction in evaporation rate, low friction with the surfaces, and capability of manipulation even on hydrophilic surfaces, liquid marbles have attracted the attention of researchers in digital microfluidics. This study investigates the manipulation of ferrofluid liquid marbles (FLMs) under DC and pulse width-modulated (PWM) magnetic fields generated by an electromagnet for the first time. At first, the threshold of the magnetic field for manipulating these FLMs is studied. Afterward, the dynamic response of the FLMs to the DC magnetic field for different FLM volumes, coil currents, and initial distances of FLM from the coil is studied, and a theoretical model is proposed. By applying the PWM magnetic field, it is possible to gain more control over the manipulation of the FLMs on the surface and adjust their position more accurately. Results indicate that with a decrease in FLM volume, coil current, and duty cycle, the FLM step length decreases; hence, FLM manipulation is more precise. Under the PWM magnetic field, it is observed that FLM movement is not synchronous with the generated pulse, and even after the coil is turned off, FLMs keep their motion. In the end, with proper adjustment of the electromagnet pulse width, launching of FLMs at a distance farther than the coil is observed.

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Section: Introductionmentioning

confidence: 99%

Experimental and Theoretical Investigation on the Dynamic Response of Ferrofluid Liquid Marbles to Steady and Pulsating Magnetic Fields

2023

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“…Ferrofluid is a colloidal suspension of magneto-responsive particles in a fluidic medium , and has found many applications in microfluidics for its controllability with magnetic stimuli, for example, in droplet manipulation, − droplet formation, − droplet splitting, double emulsion generation, shape control, mixing, and pumping . Backholm et al studied the damped oscillations of ferrofluid sessile droplets immersed in oil and developed theoretical models to describe the oscillating system .…”

Section: Introductionmentioning

confidence: 99%

Vibration and Jumping of Ferrofluid Marbles under an Initial Magnetic Perturbation

et al. 2023

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Liquid marbles are being promoted as a replacement for conventional droplets in digital microfluidics. Liquid marbles can be remotely controlled by an external magnetic field if ferrofluid is utilized as their liquid cores. In this study, the vibration and jumping of a ferrofluid marble is experimentally and theoretically investigated. An external magnetic field is utilized to induce deformation in a liquid marble and an increase in its surface energy. As the magnetic field is switched off, the stored surface energy converts to gravitational potential and kinetic energies until it is dissipated. An equivalent linear mass-spring-damper system is used to study the vibration of the liquid marble, and the effect of its volume and initial magnetic stimulus on the vibrational characteristics, such as natural frequency, damping ratio, and deformation of the liquid marble, is experimentally examined. By analyzing these oscillations, the effective surface tension of the liquid marble is evaluated. Also, a novel theoretical model is proposed to obtain the damping ratio of the liquid marble, suggesting a new tool for the measurement of liquid viscosity. Interestingly, it is observed that the liquid marble jumps from the surface in the case of high initial deformation. Based on conservation law of energy, a theoretical model for predicting the liquid marbles jumping height and the boundary between jumping and non-jumping zones in terms of nondimensional numbers, namely, magnetic and gravitational Bond numbers and Ohnesorge number, is proposed with an acceptable error compared to experimental data.

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“…Many studies have focused on droplet deformation, breakup, and generation for about a century due to their widespread applications and rich underlying physics. The dynamics of droplet formation has been investigated numerically, experimentally, and theoretically in different geometries, including nozzles 1 and lab-on-a-chip systems 2 . Droplet generation has been utilized in various applications, such as 3D printing 3 , electrosprays 4 , and bioengineering 5 .…”

Section: Introductionmentioning

confidence: 99%

On-demand ferrofluid droplet formation with non-linear magnetic permeability in the presence of high non-uniform magnetic fields

Bijarchi

Yaghoobi

Favakeh

2022

Sci Rep

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The magnetic actuation of ferrofluid droplets offers an inspiring tool in widespread engineering and biological applications. In this study, the dynamics of ferrofluid droplet generation with a Drop-on-Demand feature under a non-uniform magnetic field is investigated by multiscale numerical modeling. Langevin equation is assumed for ferrofluid magnetic susceptibility due to the strong applied magnetic field. Large and small computational domains are considered. In the larger domain, the magnetic field is obtained by solving Maxwell equations. In the smaller domain, a coupling of continuity, Navier Stokes, two-phase flow, and Maxwell equations are solved by utilizing the magnetic field achieved by the larger domain for the boundary condition. The Finite volume method and coupling of level-set and Volume of Fluid methods are used for solving equations. The droplet formation is simulated in a two-dimensional axisymmetric domain. The method of solving fluid and magnetic equations is validated using a benchmark. Then, ferrofluid droplet formation is investigated experimentally, and the numerical results showed good agreement with the experimental data. The effect of 12 dimensionless parameters, including the ratio of magnetic, gravitational, and surface tension forces, the ratio of the nozzle and magnetic coil dimensions, and ferrofluid to continuous-phase properties ratios are studied. The results showed that by increasing the magnetic Bond number, gravitational Bond number, Ohnesorge number, dimensionless saturation magnetization, initial magnetic susceptibility of ferrofluid, the generated droplet diameter reduces, whereas the formation frequency increases. The same results were observed when decreasing the ferrite core diameter to outer nozzle diameter, density, and viscosity ratios.

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Ferrofluid droplet breakup process and neck evolution under steady and pulse-width modulated magnetic fields

Cited by 16 publications

References 41 publications

Experimental and Theoretical Investigation on the Dynamic Response of Ferrofluid Liquid Marbles to Steady and Pulsating Magnetic Fields

Experimental and Theoretical Investigation on the Dynamic Response of Ferrofluid Liquid Marbles to Steady and Pulsating Magnetic Fields

Vibration and Jumping of Ferrofluid Marbles under an Initial Magnetic Perturbation

On-demand ferrofluid droplet formation with non-linear magnetic permeability in the presence of high non-uniform magnetic fields

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