Interfacial Tension Oscillations without Surfactant Transfer

Wojciechowski, Kamil; Kucharek, Marta

doi:10.1021/jp905961t

Cited by 15 publications

(11 citation statements)

References 22 publications

(27 reference statements)

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“…These findings demonstrate very strong hydrophobicity of BPh − 4 , which was effective close to the solvent criticality [31] and far from it [32]. (iii) Another intersting phenomenon is spontaneous emulsification (formation of small water droplets) at a water-nitrobenzene(NB) interface [33,34]. It was observed when a large water droplet was pushed into a cell containing NB and antagonistic salt (tetraalkylammonium chloride).…”

Section: Introductionmentioning

confidence: 81%

Solvation Effects in Phase Transitions in Soft Matter

Onuki,

Araki,

Okamoto

2010

Preprint

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Phase transitions in polar binary mixtures can be drastically altered even by a small amount of salt. This is because the preferential solvation strongly depends on the ambient composition. Together with a summary of our research in this problem, we present some detailed results on the role of antagonistic salt composed of hydrophilic and hydrophobic ions. These ions tend to segregate at liquid-liquid interfaces and selectively couple to water-rich and oil-rich composition fluctuations, leading to mesophase formation. In our two-dimensional simulation, the corasening of the domain structures can be stopped or slowed down, depending on the interaction parameter (or the temperature) and the salt density. We realize stripe patterns at the critical composition and droplet patterns at off-critical compositions. In the latter case, charged droplets emerge with considerable size dispersity in a percolated region. We also give the structure factors among the ions, accounting for the Coulomb interaction and the solvation interaction mediated by the composition fluctuations.

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Section: Introductionmentioning

confidence: 81%

Solvation Effects in Phase Transitions in Soft Matter

Onuki,

Araki,

Okamoto

2010

Preprint

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“…For example, it should be induced around a droplet of pure water (oil) inserted in a bulk oil-rich (water-rich) region in the immisible condition, where the droplet or the surrounding region contains a small amount of an antagonistic salt. The previous experiments of droplet formation [25,26] were performed in the strong segregation condition far from the solvent criticality and, as a result, the surface tension might have not been negative even after the formation of an electric double layer. Thus, experiments should also be performed on nearcritical aqueous mixtures in two-phase coexistence, where a small amount of an antagonistic salt is added to either of the water-rich or oil-rich region as in Sec.4 of this paper.…”

Section: Sa004-11mentioning

confidence: 99%

“…These findings demonstrate very strong hydrophobicity of BPh − 4 . (iv) Another interesting phenomenon is spontaneous emulsification (formation of small water droplets) at a water-NB interface [25,26]. It was observed when a large pure water droplet was pushed into a cell containing NB and antagonistic salt (tetraalkylammonium chloride).…”

Section: Introductionmentioning

confidence: 99%

Selective Solvation in Aqueous Mixtures: Interface Deformations and Instability

Ōnuki

Araki

2012

J. Phys. Soc. Jpn.

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We briefly review the effects of selective solvation of ions in aqueous mixtures, where the ion densities and the composition fluctuations are strongly coupled. We then examine the surface tension γ of a liquid-liquid interface in the presence of ions. We show that γ can be decreased drastically due to the electrostatic and solvation interactions near the interface. We calculate how the free energy is changed due to small surface undulations in the presence of an electric double layer. A surface instability occurs for negative γ, which can easily be realized for antagonistic ion pairs near the solvent criticality. Three-dimensional simulation shows how the surface instability is induced.

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“…Numerous intriguing features of the ferrofluid interfacial phenomena, such as deformations, appearance of peculiar shapes, small scale instabilities at the interface, wetting, hysteresis, merging and break-up, stretching and pinning, and many more can be fundamentally studied using the droplet systems. The motivation also comes from looking at the in-use and future possible applications of ferrofluid droplets such as micro scale mixing (Mugele et al 2006), inkjetprinting (Verkouteren & Verkouteren 2011), transport of surfactant (Wojciechowski & Kucharek 2009;Kovalchuk & Vollhardt 2001), transport of drugs in biological systems, vibrating interfaces (Kim & Lim 2015;Whitehill et al 2011) and so on.…”

Section: Introductionmentioning

confidence: 99%

Levitation of non-magnetizable droplet inside ferrofluid

Singh

Das

2018

J. Fluid Mech.

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The central theme of this work is that a stable levitation of a denser non-magnetizable liquid droplet, against gravity, inside a relatively lighter ferrofluid -a system barely considered in ferrohydrodynamics -is possible, and exhibits unique interfacial features; the stability of the levitation trajectory, however, is subject to an appropriate magnetic field modulation. We explore the shapes and the temporal dynamics of a plane non-magnetizable droplet levitating inside ferrofluid against gravity due to a spatially complex, but systematically generated, magnetic field in two dimensions. The coupled set of Maxwell's magnetostatic equations and the flow dynamic equations is integrated computationally, utilizing a conservative finite-volume based second order pressure projection algorithm combined with the front-tracking algorithm for the advection of the interface of the droplet. The dynamics of the droplet is studied under both the constant ferrofluid magnetic permeability assumption as well as for more realistic field dependent permeability described by the Langevin's non-linear magnetization model. Due to the non-homogeneous nature of the magnetic field, unique shapes of the droplet during its levitation, and at its steady state, are realized. The complete spatio-temporal response of the droplet is a function of the Laplace number La, the magnetic Laplace number La m , and the Galilei number Ga; through detailed simulations we separate out individual roles played by these non-dimensional parameters. The effect of the viscosity ratio, the stability of the levitation path and the possibility of existence of multiple-stable equilibrium states is investigated. We find, for certain conditions on the viscosity ratio, that there can be developments of cusps and singularities at the droplet surface; this phenomenon we also observe experimentally and compare with the simulations. Our simulations closely replicate the singular projection on the surface of the levitating droplet. Finally, we present an dynamical model for the vertical trajectory of the droplet. This model reveals a condition for the onset of levitation and the relation for the equilibrium levitation height. The linearization of the model around the steady state captures that the nature of the equilibrium point goes under a transition from being a spiral to a node depending upon the control parameters, which essentially means that the temporal route to the equilibrium can be either monotonic or undulating. The analytical model for the droplet trajectory is in close agreement with the detailed simulations.

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Interfacial Tension Oscillations without Surfactant Transfer

Cited by 15 publications

References 22 publications

Solvation Effects in Phase Transitions in Soft Matter

Solvation Effects in Phase Transitions in Soft Matter

Selective Solvation in Aqueous Mixtures: Interface Deformations and Instability

Levitation of non-magnetizable droplet inside ferrofluid

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