Hydrophobicity at a Janus Interface

Zhang, Xueyan; Zhu, Yunhua; Granick, Steve

doi:10.1126/science.1066141

Cited by 157 publications

(156 citation statements)

References 26 publications

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“…However, our NR measurements are not consistent with some AFM studies of preexisting bubbles that are tens of nanometers in size (10,(14)(15)(16)(17). 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␦.…”

Section: Resultsmentioning

confidence: 38%

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Doshi

Watkins

Israelachvili

et al. 2005

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

252

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: Resultsmentioning

confidence: 38%

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Doshi

Watkins

Israelachvili

et al. 2005

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

252

264

View full text Add to dashboard Cite

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“…In an intriguing experiment Granick and coworkers investigated just such a system. They studied a Janus interface in which a water slab is trapped between a hydrophobic wall on one side and a hydrophilic wall on the other [46] and found that it prevents any macroscopic drying or cavitation of the liquid, which in any case would be strongly affected even by relatively weak van der Waals forces.…”

Section: Introductionmentioning

confidence: 99%

Hydrophobic Interactions and Dewetting between Plates with Hydrophobic and Hydrophilic Domains

2009

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We study by molecular dynamics simulations the wetting/dewetting transition and the dependence of the free energy on distance between plates that contain both hydrophobic and hydrophilic particles. We show that dewetting and strength of hydrophobic interaction is very sensitive to the distribution of hydrophobic and hydrophilic domains. In particular, we find that plates characterized by a large domain of hydrophobic sites induce a dewetting transition and an attractive solvent-induced interaction. On the other hand, a homogeneous distribution of the hydrophobic and hydrophilic particles on the plates prevents the dewetting transition and produces a repulsive solvent-induced interaction. We also present results for a kind of "Janus interface" in which one plate consists of hydrophobic particles and the other of hydrophilic particles showing that the inter-plate gap remains wet until steric constraints at small separations eject the water molecules.Our results indicate that the Cassie equation, for the contact angle of a heterogeneous plate, can not be used to predict the critical distance of dewetting. These results indicate that hydrophobic interactions between nanoscale surfaces with strong large length-scale hydrophobicity can be highly cooperative and thus they argue against additivity of the hydrophobic interactions between different surface domains in these cases.

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“…Even in the absence of directional forces between the walls and liquid molecules, wetting by water is asymmetric, enhanced at the wall at which the field points into the aqueous phase and almost unchanged at the opposite side 9 (Janus interface) 12 . We explain the sign-sensitive response to the field 9 in terms of orientation preferences of surface molecules.…”

Section: Introductionmentioning

confidence: 99%

Water-mediated ordering of nanoparticles in an electric field

2009

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Interfacial polar molecules feature a strongly anisotropic response to applied electric field, favoring dipole orientations parallel to the interface. In water, in particular, this effect combines with generic orientational preferences induced by spatial asymmetry of water hydrogen bonding under confined geometry, which may give rise to a Janus interface. The two effects manifest themselves in considerable dependence of water polarization on both the field direction relative to the interface, and the polarity (sign) of the field. Using molecular simulations, we demonstrate strong field-induced orientational forces acting on apolar surfaces through water mediation. At a field strength comparable to electric fields around a DNA polyion, the torques we predict to act on an adjacent nanoparticle are sufficient to overcome thermal fluctuations. These torques can align a particle with surface as small as 1 nm 2 . The mechanism can support electrically controlled ordering of suspended nanoparticles as a means of tuning their properties, and can find application in electro-nanomechanical devices.

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Hydrophobicity at a Janus Interface

Cited by 157 publications

References 26 publications

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

Hydrophobic Interactions and Dewetting between Plates with Hydrophobic and Hydrophilic Domains

Water-mediated ordering of nanoparticles in an electric field

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