Nanoscale Wetting Under Electric Field from Molecular Simulations

Daub, Christopher D.; Bratko, D.; Luzar, Alenka

doi:10.1007/128_2011_188

Cited by 29 publications

(39 citation statements)

References 123 publications

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“…The presence of electrostatic field may change the properties of water. For instance, applying electrostatic field or adding ions to water confined in ion channels and carbon nanotubes leads to the increase of water density, also called “electrostriction” 14 16 26 27 28 . Such phenomenon is generally found when field exposed water is held in equilibrium with a non-perturbed reservoir 15 27 29 .…”

Section: Resultsmentioning

confidence: 99%

Electrostatic field-exposed water in nanotube at constant axial pressure

Sun

Koga

et al. 2014

Sci Rep

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Water confined within nanoscale geometries under external field has many interesting properties which is very important for its application in biological processes and engineering. Using molecular dynamics simulations, we investigate the effect of external fields on polarization and structure as well as phase transformations of water confined within carbon nanotubes. We find that dipoles of water molecules tend to align along external field in nanoscale cylindrical confinement. Such alignment directly leads to the longitudinal electrostriction and cross-sectional dilation of water in nanotube. It also influences the stability of ice structures. As the electrostatic field strengthens, the confined water undergoes phase transitions from a prism structure to a helical one to a single chain as the electrostatic field strengthens. These results imply a rich phase diagram of the confined water due to the presence of external electriostatic field, which can be of importance for the industrial applications in nanopores.

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Section: Resultsmentioning

confidence: 99%

Electrostatic field-exposed water in nanotube at constant axial pressure

Sun

Koga

et al. 2014

Sci Rep

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“…However, significant efforts have been made in recent studies to obtain a fundamental understanding of hydrophobicity at the molecular level. [7][8][9][10][11][12][13][14][15][16] For example, it has been reported that hydrophobicity is influenced by the size and structure of water droplets on a surface, 12 the surface morphology, 8,9 and environmental conditions such as external fields and pressure. [13][14][15][16] Icephobicity, the term coined to describe the ice-repellent properties of substances, has also received much attention recently, owing to its little-known features and potential applications.…”

Section: Introductionmentioning

confidence: 99%

Diameter-dependent hydrophobicity in carbon nanotubes

Kyakuno

Fukasawa

Ichimura

et al. 2016

The Journal of Chemical Physics

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Diameter-dependent hydrophobicity in carbon nanotubesSingle-wall carbon nanotubes (SWCNTs) are a good model system that provides atomically smooth nanocavities. It has been reported that water-SWCNTs exhibit hydrophobicity depending on the temperature T and the SWCNT diameter D. SWCNTs adsorb water molecules spontaneously in their cylindrical pores around room temperature, whereas they exhibit a hydrophilic-hydrophobic transition or wet-dry transition (WDT) at a critical temperature T wd ≈ 220-230 K and above a critical diameter D c ≈ 1.4-1.6 nm. However, details of the WDT phenomenon and its mechanism remain unknown. Here, we report a systematic experimental study involving X-ray diffraction, optical microscopy, and differential scanning calorimetry. It is found that water molecules inside thick SWCNTs (D > D c ) evaporate and condense into ice Ih outside the SWCNTs at T wd upon cooling, and the ice Ih evaporates and condenses inside the SWCNTs upon heating. On the other hand, residual water trapped inside the SWCNTs below T wd freezes. Molecular dynamics simulations indicate that upon lowering T, the hydrophobicity of thick SWCNTs increases without any structural transition, while the water inside thin SWCNTs (D < D c ) exhibits a structural transition, forming an ordered ice. This ice has a well-developed hydrogen bonding network adapting to the cylindrical pores of the SWCNTs. Thus, the unusual diameter dependence of the WDT is attributed to the adaptability of the structure of water to the pore dimension and shape. Published by AIP Publishing.[http://dx

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“…Before discussing the electrowetting number in Eq. ( 21) obtained within the present density functional analysis, the traditional approach based on the assumption of electrowetting being an electrocapillarity effect [2,3,5,[7][8][9][10][11][12][13][14][15][16][17][18][19] is repeated. Here only the classical method based on Lippmann's equation is presented.…”

Section: A Electrowetting and Electrocapillaritymentioning

confidence: 99%

“…( 17) from U = ψ +α − ψ −α and σ +α + σ −α = 0 as ψ ±α = ±U/2. This leads to the commonly used form of the electrowetting equation [2,3,5,[7][8][9][10][11][12][13][14][15][16][17][18][19]]…”

Section: A Electrowetting and Electrocapillaritymentioning

confidence: 99%

“…Since the pioneering work of Lippmann [1] and Pellat [2,3] on the influence of electrostatic potentials on the wetting of substrates by fluids, electrowetting has been simultaneously studied to address fundamental issues of surface science, e.g., electrocapillarity [4], the structure of solid-fluid interfaces [5], or the characterization of surface states [6], as well as to develop novel applications, e.g., driving, mixing, or shaping of droplets in lab-on-a-chip devices, optical applications, or microelectromechanical systems [7]. In the past electrowetting at low voltages was commonly interpreted as an electrocapillarity effect, i.e., it is assumed to hinge on the voltage-dependence of the substrate-fluid interfacial tension [2,3,5,[7][8][9][10][11][12][13][14][15][16][17][18][19]. A justification for this approach is frequently given in terms of the vast experimental evidence for systems of uncoated and hydrophobically coated electrodes.…”

Section: Introductionmentioning

confidence: 99%

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Density functional theory of electrowetting

Bier

Ibagon

2014

Phys. Rev. E

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The phenomenon of electrowetting, i.e., the dependence of the macroscopic contact angle of a fluid on the electrostatic potential of the substrate, is analyzed in terms of the density functional theory of wetting. It is shown that electrowetting is not an electrocapillarity effect, i.e., it cannot be consistently understood in terms of the variation of the substrate-fluid interfacial tension with the electrostatic substrate potential, but it is related to the depth of the effective interface potential. The key feature, which has been overlooked so far and which occurs naturally in the density functional approach is the structural change of a fluid if it is brought into contact with another fluid. These structural changes occur in the present context as the formation of finite films of one fluid phase in between the substrate and the bulk of the other fluid phase. The non-vanishing Donnan potentials (Galvani potential differences) across such film-bulk fluid interfaces, which generically occur due to an unequal partitioning of ions as a result of differences of solubility contrasts, lead to correction terms in the electrowetting equation, which become relevant for sufficiently small substrate potentials. Whereas the present density functional approach confirms the commonly used electrocapillarity-based electrowetting equation as a good approximation for the cases of metallic electrodes or electrodes coated with a hydrophobic dielectric in contact with an electrolyte solution and an ion-free oil, a significantly reduced tendency for electrowetting is predicted for electrodes coated with a dielectric which is hydrophilic or which is in contact with two immiscible electrolyte solutions.

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Nanoscale Wetting Under Electric Field from Molecular Simulations

Cited by 29 publications

References 123 publications

Electrostatic field-exposed water in nanotube at constant axial pressure

Electrostatic field-exposed water in nanotube at constant axial pressure

Diameter-dependent hydrophobicity in carbon nanotubes

Density functional theory of electrowetting

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