Is There a Thin Film of Air at the Interface between Water and Smooth Hydrophobic Solids?

Mao, Min; Zhang, Jinhong; Yoon, Roe‐Hoan; Ducker, William A.

doi:10.1021/la0361722

Cited by 81 publications

(72 citation statements)

References 43 publications

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“…We also note that extended depletion layers as extracted from the neutron data should also show up in optical ellipsometry where no such profiles were found (22,23). Furthermore, no indication for the influence of gases dissolved into the water on the hydrophobic gap (d Ͻ 2.5 Å) was found in heat conductance measurements (24).…”

Section: Resultsmentioning

confidence: 75%

High-resolution in situ x-ray study of the hydrophobic gap at the water–octadecyl-trichlorosilane interface

Mezger

Reichert

Schöder

et al. 2006

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

263

231

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The knowledge of the microscopic structure of water at interfaces is essential for the understanding of interfacial phenomena in numerous natural and technological environments. To study deeply buried liquid water-solid interfaces, high-energy x-ray reflectivity measurements have been performed. Silicon wafers, functionalized by a self-assembled monolayer of octadecyltrichlorosilane, provide strongly hydrophobic substrates. We show interfacial density profiles with angstrom resolution near the solid-liquid interface of water in contact with an octadecyltrichlorosilane layer. The experimental data provide clear evidence for the existence of a hydrophobic gap on the molecular scale with an integrated density deficit d ‫؍‬ 1.1 Å g cm ؊3 at the solid-water interface. In addition, measurements on the influence of gases (Ar, Xe, Kr, N2, O2, CO, and CO2) and HCl, dissolved in the water, have been performed. No effect on the hydrophobic water gap was found.hydrophobicity ͉ interfacial water ͉ x-ray reflectivity H ydrophobicity, i.e., the repulsion of water, is a well known phenomenon in our environment (1). The generic hydrophobic interaction occurs between a nonpolar molecule and the water molecule. In bulk water, the hydrophobic interaction leads to the so-called hydrophobic hydration of unpolar solvents which generically results in a reduced density and an increased heat capacity. The seminal study on the thermodynamics of nonpolar solvation goes back to Frank and Evans in the mid-1940s (2). While of course the details of structural ordering remained unclear, it became evident that nonpolar solvation is a negentropic process which appeared later to become a key element to understand protein folding and stability (3). The microscopic details of how the nonpolar molecules interact with each other in water is a key information to understand how proteins and biological membranes maintain their structural integrity. Today we know that hydrophobic bonds are a major force driving proper protein folding, and that the interplay between hydrophobic and hydrophilic interactions is important to stabilize the shape of biological structures, such as proteins and cell membranes (4).Hydrophobic surfaces are of particular interest, since they control many interfacial phenomena in biology and technology. However, the microscopic details of how water meets a hydrophobic interface are still not settled and in fact rather controversial. A basic missing piece of information is the size of the hydrophobic gap between the water phase and the hydrophobic surface. Wetting studies on mesoporous silica (5) indicate that water is separated from the hydrophobic walls by a vapor gap of thickness 3-4 Å. Molecular dynamics simulations carried out for liquid water between f lat hydrophobic surfaces predict density oscillations extending up to 10 Å into the adjacent water accompanied by a molecular orientational order affecting a water layer of 7 Å. The simulations, as well as the results from surface vibrational spectroscopy, show that the water mole...

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Section: Resultsmentioning

confidence: 75%

High-resolution in situ x-ray study of the hydrophobic gap at the water–octadecyl-trichlorosilane interface

Mezger

Reichert

Schöder

et al. 2006

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

263

231

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show abstract

“…Neutron [547] and X-ray [548] reflectivity experiments confirmed the observed reduced density of water at the interface, while experiments with an ellipsometer excluded nanobubbles on silanated silica [549]. There is now strong evidence, that bridging bubbles contribute to the long-range hydrophobic attraction in many experiments [495] but the whole hypothesis and the effect of nanobubbles are still being debated [550].…”

Section: Hydrophobic Attractionmentioning

confidence: 78%

Force measurements with the atomic force microscope: Technique, interpretation and applications

Butt

Cappella

Kappl

2005

Surface Science Reports

3,246

2,949

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“…If there are some tiny defects or voids on the surface, the defects tend to become nucleations to capture gas and then form nanobubbles [30][31][32]. Figure 1 showed the height image and the cross-sectional analysis of the nanobubbles generated on HOPG surface by direct immersion method.…”

Section: Resultsmentioning

confidence: 99%

Oxygen release from nanobubbles adsorbed on hydrophobic particles

Zhao¹,

Hu²,

Juan³

et al. 2014

Chemical Physics Letters

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Is There a Thin Film of Air at the Interface between Water and Smooth Hydrophobic Solids?

Cited by 81 publications

References 43 publications

High-resolution in situ x-ray study of the hydrophobic gap at the water–octadecyl-trichlorosilane interface

High-resolution in situ x-ray study of the hydrophobic gap at the water–octadecyl-trichlorosilane interface

Force measurements with the atomic force microscope: Technique, interpretation and applications

Oxygen release from nanobubbles adsorbed on hydrophobic particles

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