Field-induced control of ferrofluid emulsion rheology and droplet break-up in shear flows

Cunha, Lucas Hildebrand Pires da; Siqueira, Ivan R.; Oliveira, Taygoara Felamingo de; Ceniceros, Héctor D.

doi:10.1063/1.5055943

Cited by 35 publications

(35 citation statements)

References 47 publications

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“…Another assumption which often is tacitly made when dealing with ferrofluids, is the hypothesis that any field-induced non-uniformity of concentration of the ferromagnetic (or ferrimagnetic) particles dispersed in the carrier fluid can be neglected (see [42,43,[53][54][55][56], for instance). This simplification can be questionable, [57] especially when large magnetic fields are considered (in these conditions, field-induced assemblies may appear even for relatively small particle concentrations [58]).…”

Section: Problem Formulationmentioning

confidence: 99%

“…Aside from viscous (and possibly inertial [24]) effects arising from the presence of an imposed flow, the configuration of the dispersed phase can also be altered by additional stresses of different nature, such as electric fields (e.g., see [37][38][39]) and magnetic fields [40][41][42][43][44]. In the latter case, at least one phase must be composed of a magnetizable material.…”

Section: Introductionmentioning

confidence: 99%

“…To the best of our knowledge, the abovementioned works of Cunha et al [42,43] and Ishida and Matsunaga [44] are the only aimed at investigating the rheology of emulsions in the presence of a ferrofluid phase and an imposed magnetic field. Previous works, on the other hand, have been devoted to the study of non-rheological properties such as emulsion magnetic permeability, for emulsions of ferrofluid drops in non-magnetizable fluids (e.g., see Refs.…”

Section: Introductionmentioning

confidence: 99%

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Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a nonmagnetizable carrier fluid under the influence of a uniform magnetic field

Capobianchi

Lappa

Oliveira

et al. 2021

Journal of Rheology

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The effect of a spatially uniform magnetic field on the shear rheology of a dilute emulsion of monodispersed ferrofluid droplets, immersed in a non-magnetizable immiscible fluid, is investigated using direct numerical simulations. The direction of the applied magnetic field is normal to the shear flow direction. The droplets extra stress tensor arising from the presence of interfacial forces of magnetic nature is modeled on the basis of the seminal work of G. K. Batchelor, J. Fluid Mech., 41.3 (1970) under the assumptions of a linearly magnetizable ferrofluid phase and negligible inertia. The results show that even relatively small magnetic fields can have significant consequences on the rheological properties of the emulsion due to the magnetic forces that contribute to deform and orient the droplets towards the direction of the applied magnetic vector. In particular, we have observed an increase of the effective (bulk) viscosity and a reversal of the sign of the two normal stress differences with respect to the case without magnetic field for those conditions where the magnetic force prevails over the shearing force. Comparisons between the results of our model with a direct integration of the viscous stress have provided an indication of its reliability to predict the effective viscosity of the suspension. Moreover, this latter quantity has been found to behave as a monotonic increasing function of the applied magnetic field for constant shearing flows ("magneto-thickening" behaviour), which allowed us to infer a simple constitutive equation describing the emulsion viscosity.

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Section: Problem Formulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a nonmagnetizable carrier fluid under the influence of a uniform magnetic field

Capobianchi

Lappa

Oliveira

et al. 2021

Journal of Rheology

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“…Readers may also refer to few other articles for the recent developments and investigations on the dynamics of ferrofluid droplets. [24][25][26][27][28] The coalescence of ferrofluid droplets under the effect of an external magnetic field is not addressed comprehensively in the literature. Only a few attempts have been made in the development of fundamental principles and governing factors of magneto coalescence.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental and numerical investigations are performed on the consolidation and deformation of bubbles within ferrofluids by Lee et al 23 To suppress the bubbles merging they used a VOF method with the incorporation of a multiple‐color function technique. Readers may also refer to few other articles for the recent developments and investigations on the dynamics of ferrofluid droplets 24‐28 …”

Section: Introductionmentioning

confidence: 99%

Motion, deformation, and coalescence of ferrofluid droplets subjected to a uniform magnetic field

Khan

Niu

et al. 2020

Numerical Methods in Fluids

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In this article, we present the motion, deformation, and coalescence of ferrofluid droplets suspended in a nonmagnetic fluid, subjected to a uniform magnetic field in both vertical and horizontal directions. A coupling between the simplified multiphase lattice Boltzmann method and the self-correcting scheme is constructed to numerically solve the two-dimensional flow field and the magnetostatics equations, respectively. The Cahn-Hilliard equation is employed to seize the diffuse interface between magnetic and nonmagnetic fluids. In order to validate the model, deformation of a ferrofluid droplet suspended in nonmagnetic fluid is simulated as a test case and the results are compared with numerical and experimental results. Furthermore, a detailed analysis on the behavior of falling ferrofluid droplets and the coalescence between a pair of ferrofluid droplets under the effect of different magnetic fields and different droplets configurations are also presented in this article. The results provide significant insight and a better understanding of these phenomena. It is found that for higher values of magnetic bond number and susceptibility, the droplet deformation is significant and the falling process is faster while a reverse behavior is observed for higher values of Eötvös number. Moreover, the magnetic energy density exhibits an interesting behavior in the vicinity of the droplets. It is concentrated between the droplets with a nonuniform distribution when the droplets are close to each other.

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Horizontal and Vertical Coalescent Microrobotic Collectives Using Ferrofluid Droplets

et al. 2023

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Many artificial miniature robotic collectives have been developed to overcome the inherent limitations of inadequate individual capabilities. However, the basic building blocks of the reported collectives are mainly in the solid state, where the morphological boundaries of internal individuals are clear and cannot genuinely merge. Miniature robotic collectives based on liquid units still need to be explored; such on‐demand mergeable swarm systems are advantageous for adapting to the changing external environment. Here, a strategy to achieve a coalescent collective system we presented that exploits the ferrofluid droplets' splitting and coalescence properties to trigger the formation of horizontal multimodal and vertical gravity‐resistant collectives and unveil pattern‐enabled robotic functionalities. When subjected to a time‐varying magnetic field, the droplet swarm exhibits a variety of morphologies ranging from horizontal collectives, including vortex‐like, chain‐like, and crystal‐like patterns to vertical layer‐upon‐layer patterns. Using experiments and simulations, the formation and transformation of different morphological collectives are shown and their robust environmental adaptability are demonstrated. Potential applications of the multimodal droplet collectives are presented, including exploring an unknown environment, targeted object delivery, and fluid flow filtration in a lab‐on‐a‐chip. This work may facilitate the design of microrobotic swarm systems and expand the range of materials for miniature robots.

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Field-induced control of ferrofluid emulsion rheology and droplet break-up in shear flows

Cited by 35 publications

References 47 publications

Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a nonmagnetizable carrier fluid under the influence of a uniform magnetic field

Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a nonmagnetizable carrier fluid under the influence of a uniform magnetic field

Motion, deformation, and coalescence of ferrofluid droplets subjected to a uniform magnetic field

Horizontal and Vertical Coalescent Microrobotic Collectives Using Ferrofluid Droplets

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