Lattice study of a Janus interface

McCormick, Thomas A.

doi:10.1103/physreve.68.061601

Cited by 8 publications

(14 citation statements)

References 12 publications

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“…Fig. 1) that is also consistent with the data for naturally aerated water, where local random diffuse density fluctuations (with a maximum possible lateral spacing, Y, of 10 m with no minimum limit) are shown based on expectations from computer simulations (25,39,40). Other molecular models also can fit the data, such as small fluctuating cavities of about the same size as those shown here but with sharper liquid-vapor interfaces.…”

Section: Resultssupporting

confidence: 73%

“…The statistical nature of the nucleation process (25,39,40), depending as it would on the time the surfaces remain at a given separation, could make it difficult to express this interaction in terms of an equilibrium potential function, which could be the reason why experiments such as surface forces apparatus, AFM, and colloidal stability studies, Fig. 1.…”

Section: Resultsmentioning

confidence: 99%

“…To fit our data, the surface coverage of the nanobubbles would have to be Ͼ90% and their average height would have to be Ͻ11 Å, making them thermodynamically unstable under static conditions, providing another reason for considering them as fluctuating entities (38). In addition, the amplitude and frequency of the fluctuations at one hydrophobic surface would be expected to be enhanced by the close proximity of a second hydrophobic surface, allowing for vapor bridges to form [depending on the surface separation, area, and time (25,39,40)] that would pull the surfaces together with a strong capillary force acting over a range significantly greater than twice the original reduced water density length, 2␦. To test for reversibility, we vacuum degassed one D 2 O sample for 1 h, then allowed air to diffuse back in.…”

Section: Resultsmentioning

confidence: 99%

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Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Doshi

Watkins

Israelachvili

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

253

264

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Here, direct noninvasive neutron reflectivity measurements reveal the presence of a reduced (deuterated) water density region, with a sigmoidal density profile at the hydrophobic silane-water interface that depends on the type and concentration of dissolved gases in the water. Removal of dissolved gases decreases the width of the reduced water density region, and their reintroduction leads to its increase. When compared with recent computer simulations, a locally fluctuating density profile is proposed, whereas preexisting nanobubbles are excluded. The presence of a fluctuating reduced water density region between two hydrophobic surfaces and the attractive ''depletion force'' to which it leads may help explain the hydrophobic force and its reported diminution in deaerated water. Our results are also quantitatively consistent with recent dynamic surface force apparatus results that drastically revise previous estimates of the slip length of water flowing past hydrophobic surfaces from microns to Ϸ20 nm. Our observations, therefore, go a long way toward reconciling three quite different types of experiments and phenomena: water depletion at hydrophobic surfaces, water slip at hydrophobic surfaces, and the hydrophobic interaction.interfacial water ͉ neutron reflectivity ͉ slip conditions

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Doshi

Watkins

Israelachvili

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

253

264

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“…It is generally agreed that water is attracted at best only weakly to a hydrophobic surface. The matter of soft modes and ensuing fluctuations of interfacial density, which might have very long wavelength, has been emphasized on the theoretical side [7], inferred from measurements [8], and reported from one simulation [9]. To this fresh question, we encourage the community to turn its attention.…”

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confidence: 99%

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et al. 2008

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Poynor et al. Reply: Ocko, Dhinojwala, and Daillant agree with us about the role of methyl groups. Our unambiguous statement that [1] ''. . .the depletion thickness reported in Fig. 2(b) must be regarded as an upper bound, although the existence of the depletion layer is unequivocal. This is because protons on the methyl-terminated hydrophobic monolayer and on water adjoining the monolayer are virtually invisible. . .'' has been misquoted by Ocko, Dhinojwala, and Daillant, who assert [2] ''(their) entire electron density depletion is attributed to a depletion of water.'' Our Table I corrects additional factual mistakes in Table I of Ocko, Dhinojwala, and Daillant regarding data in the literature [1,3]. The product of the gap thickness and the electron density deficit is more consistent between the limits of the fitting range than Ocko, Dhinojwala, and Daillant have claimed. Table I also includes new experiments in which we tested experimentally our claim of a significant depletion by considering a counterexample, the interface of ethanol with octadecyltriethoxysiloxane (OTE) methyl-terminated monolayers. Measuring the reflectivity of this wetted structure under the same conditions as in our original work, we obtain the finding that methyl groups of the OTE monolayer explain all of the electron density gap for the wetting case but only half of that observed in our original [1] data.Ocko, Dhinojwala, and Daillant suggest a second contribution to the observed electron density depletion --surface-induced orientation of water [2]. We note that this phenomenon, if substantiated, would be an intrinsic aspect of hydrophobicity. The large literature on this question suggests a certain statistical bias for one of the two hydrogen bonds of the average water molecule to point towards a hydrophobic surface, giving a broad orientational distribution [4,5]-not the distinct smecticlike layering proposed by Ocko, Dhinojwala, and Daillant. These simulations therefore do not support the contention that orientational ordering of water is a dominant source of electron density depletion when water meets a hydrophobic surface. Ocko, Dhinojwala, and Daillant also assert that low-density regions at the calcite-water interface observed by x-ray experiments are associated with water orientation [6]. The low-density layer observed in that system is not, however, from number density depletion. It is, instead, due to the intrinsic structure of the interfacial hydration layer coupled with high (1 Å ) resolution in those measurements.We are gratified that the frame of discourse has shifted from controversies of whether a zone of depleted electron density exists, which was the main point of our Letter, and on which we and Ocko, Dhinojwala, and Daillant agree. It is generally agreed that water is attracted at best only weakly to a hydrophobic surface. The matter of soft modes and ensuing fluctuations of interfacial density, which might have very long wavelength, has been emphasized on the theoretical side [7], inferred from measurements [8], and...

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“…Biomimetic research gives scientists much inspiration to realize the special wettability on functional surfaces, which may bring great advantages in a wide variety of application areas. 20,21 It is then interesting to consider the asymmetric situation 22 that the behavior of fluid in nanochannel has one hydrophobic and one hydrophilic plate, the so-called Janus interface. 20 The objective of the present study is to investigate the behavior of gas flow in nanochannel with a Janus interface (NCJI) using molecular dynamics simulation.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of gas flow in nanochannel with a Janus interface

Xie

Liu

2012

AIP Advances

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It is interesting to investigate fluid flow in nanochannel with a Janus interface (NCJI), especially when considering the asymmetric situations of wettability in the biology. The simulation results show that the temperature has a significant influence on the particle number near the hydrophilic surface because the desorption increases with the fluid temperature, while the external force has a little influence on the mass distribution. Because the viscosity of gas increases with temperature, the flow velocity of gas in NCJI decreases as the wall temperature increases. The flow in NCJI is neither Poiseuille-like nor plug-flow behaviors. This particular form of flow may be able to help us invent new nano-devices

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Lattice study of a Janus interface

Cited by 8 publications

References 12 publications

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Poynoret al.Reply:

Molecular dynamics simulations of gas flow in nanochannel with a Janus interface

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