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Transport of a Sessile Aqueous Droplet over Spikes of Oil Based Ferrofluid in the Presence of a Magnetic Field

Mandal, C ; Banerjee, U ; Sen, A. K

Langmuir, 2019-06, Vol.35 (25), p.8238-8245, Article acs.langmuir.9b00631 [Periódico revisado por pares]

United States: American Chemical Society

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  • Título:
    Transport of a Sessile Aqueous Droplet over Spikes of Oil Based Ferrofluid in the Presence of a Magnetic Field
  • Autor: Mandal, C ; Banerjee, U ; Sen, A. K
  • É parte de: Langmuir, 2019-06, Vol.35 (25), p.8238-8245, Article acs.langmuir.9b00631
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
  • Descrição: Droplets can be used as carrier vehicles for the transportation of biological and chemical reagents. Manipulation of water- and oil-based ferromagnetic droplets in the presence of a magnetic field has been well-studied. Here, we elucidate the transport of a sessile aqueous (diamagnetic) droplet placed over spikes of oil-based ferrofluid (FF) in the presence of a nonuniform magnetic field. An oil-based FF droplet, dispensed over a rigid oleophilic surface, interacts with a magnetic field to get transformed into an array of spikes which then act as a carrier for the transportation of the aqueous droplet. Our study reveals that transportation phenomena is governed by the interplay of three different forces: magnetic force F m, frictional force F f, and interfacial tension force F i, which is expressed in terms of the magnetic Laplace number (La m) and magnetic Bond number (Bo m) as La m –1 = (F f1/F m,x ) and Bo m La m –1 = (F f2/F i). Based on the values of the dimensionless numbers, three different regimes, steady droplet transport, spike extraction, and magnet disengagement, are identified. It is found that steady droplet transport is observed for La m –1 ≤ 1 and Bo m La m –1 ≤ 1, whereas extraction of spikes is observed for La m –1 ≤ 1 and Bo m La m –1 > 1 and magnet disengagement is observed for La m –1 > 1. In the steady droplet transport regime, velocity of the aqueous droplet U ds was found to be dependent on the volumes of the aqueous droplet V w and FF droplet V FF following U ds ∼ V w –0.19 V FF 0.36. A simple model is presented that accurately predicts the aqueous droplet velocity U ds within 5% of the corresponding experimental data. In the spike extraction regime, the spike extraction distance L se was found to vary with V w, V FF, and the magnet velocity U ms following L se ∼ V w –1.75 V FF 0.75 U ms –1.56.
  • Editor: United States: American Chemical Society
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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