Título:	Magnetic field effects on the surfactant concentration over ferrofluid droplet surfaces in shear flows
Autor(es):	Pimenta, Paulo Henrique Neves Rebouças, Rodrigo B. Oliveira, Taygoara Felamingo de
ORCID:	https://orcid.org/0000-0002-4145-5461 https://orcid.org/0000-0001-8982-3553 https://orcid.org/0000-0003-2957-537X
Afiliação do autor:	Federal Institute of Goiás, Department of Academic Areas IV University of Illinois Chicago, Department of Chemical Engineering University of Brasília, Department of Mechanical Engineering, Laboratory of Energy and Environment
Assunto:	Campo magnético Surfactantes Cisalhamento
Data de publicação:	15-Mai-2024
Editora:	Elsevier Inc.
Referência:	PIMENTA, P. H. N.; REBOUÇAS, R. B.; OLIVEIRA, T. F. Magnetic field effects on the surfactant concentration over ferrofluid droplet surfaces in shear flows. Journal of Colloid and Interface Science, [S. l.], v. 662, 15 maio 2024, p. 438-445. DOI: https://doi.org/10.1016/j.jcis.2024.02.036.
Abstract:	We investigate the impact of a magnetic field on surfactant concentration and interfacial forces across droplet surfaces within shear flows. Our analysis centers on a single two-dimensional ferrofluid droplet covered with surfactants, suspended in an immiscible, non-magnetizable liquid. The model combines incompressible Navier–Stokes equations and Maxwell's equations in the superparamagnetic limit in the single-fluid formulation, augmented by terms accounting for Marangoni, capillary, and magnetic forces at the droplet interface. We solve the surfactant convection-diffusion equation at the surface, while a non-linear Langmuir equation of state relates surfactant concentration to surface tension. The model is numerically solved using finite differences, a level-set method for multiphase flow computation, and the closest-point method for concentration equation. Our findings reveal that even though the surfactant is magnetically neutral, the presence of a magnetic field significantly modifies its distribution at the interface. A magnetic field perpendicular to the primary flow direction shifts the maximum concentration zone from the droplet tips toward the flow vorticity direction, while a parallel field produces the opposite effect. Alterations in surfactant distribution directly impact the surface tension field, offering a potential wireless means of controlling droplet dynamics.
Unidade Acadêmica:	Faculdade de Tecnologia (FT) Departamento de Engenharia Mecânica (FT ENM)
DOI:	https://doi.org/10.1016/j.jcis.2024.02.036
Versão da editora:	https://www.sciencedirect.com/science/article/abs/pii/S0021979724002728?via%3Dihub
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