Lubrication by molecularly thin water films confined between nanostructured membranes

Kalra, Amrit; Garde, Shekhar; Hummer, Gerhard

doi:10.1140/epjst/e2010-01317-9

Cited by 11 publications

(12 citation statements)

References 32 publications

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“…Our results suggest that such observations are just a coincidence: Should hydrophilic surfaces be manufactured with high density of adsorption sites close enough to each other to allow water molecules to easily migrate from one to the next, such hydrophilic surfaces could show liquid slip. Our interpretation is consistent with a recent simulation study for the thermal diffusion of carbon nanotube membranes (21), with the molecular mechanism proposed for liquid slip (22), and with experimental observations reported for alkanes (23). Our interpretation could also explain the experimental results by McCarthy and coworkers (24), according to which the contact angle hysteresis, and not the static contact angle, should be used, macroscopically, to determine the hydrophobic vs. hydrophilic character of a surface.…”

Section: Resultssupporting

confidence: 92%

Liquid water can slip on a hydrophilic surface

Papavassiliou

Lee

et al. 2011

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

235

199

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Understanding and predicting the behavior of water, especially in contact with various surfaces, is a scientific challenge. Molecularlevel understanding of hydrophobic effects and their macroscopic consequences, in particular, is critical to many applications. Macroscopically, a surface is classified as hydrophilic or hydrophobic depending on the contact angle formed by a water droplet. Because hydrophobic surfaces tend to cause water slip whereas hydrophilic ones do not, the former surfaces can yield self-cleaning garments and ice-repellent materials whereas the latter cannot. The results presented herein suggest that this dichotomy might be purely coincidental. Our simulation results demonstrate that hydrophilic surfaces can show features typically associated with hydrophobicity, namely liquid water slip. Further analysis provides details on the molecular mechanism responsible for this surprising result.P rotein folding (1), micelle and cellular membrane formation (2), and frictionless flow of water through carbon nanotube membranes (3-5) are only some manifestations of hydrophobic effects. Flat surfaces are arbitrarily classified as hydrophobic when a water droplet yields a contact angle larger than 90°, hydrophilic otherwise. A now famous 2008 commentary by Granick and Bae (6) initiated a scientific discussion to identify the molecular signature of hydrophobic vs. hydrophilic surfaces. The question is whether or not molecular properties exist for interfacial water molecules that change with the surface "degree of hydrophobicity." Identifying such properties could advance practical applications (e.g., designing self-cleaning surfaces) as well as fundamental scientific endeavors including understanding self-assembly (7).Molecular simulations should allow the discovery of such molecular signatures because they allow a systematic variation of the properties of a surface, as well as of surface-water interactions (8). Although the resultant substrates may not be realistic, the results are useful to interpret nature and to design innovative materials. It has so far been possible to relate some macroscopic observables to the degree of hydrophobicity [i.e., contact angle to adsorption free energy (9)]. Garde and coworkers employed equilibrium molecular dynamics (MD) to determine a number of quantities, including local density, contact angle, and adsorption of small solutes for water near surfaces of varying degrees of hydrophobicity (10). Whereas the local water density provided unsatisfactory characterization, the probability of cavity formation was found to be large near hydrophobic and small near hydrophilic surfaces.The present work focuses on the relation between one important macroscopic signature of hydrophobic surfaces, the hydrodynamic liquid slip, to molecular interfacial water properties. Large liquid slip on hydrophobic surfaces could reduce the drag in vessels navigating the seas, the pressure drop encountered by fluids flowing inside pipes, and even repel ice formation. Liquid slip seems to appear when ...

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Section: Resultssupporting

confidence: 92%

Liquid water can slip on a hydrophilic surface

Papavassiliou

Lee

et al. 2011

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

235

199

View full text Add to dashboard Cite

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“…105 The absence of inter-layer hydrogen bonds evidently imparts significant additional translational and rotational freedom to the molecules in this phase compared to the multilayer phase, but is countered by the severe geometric restrictions to relative motion imposed by confinement within such a narrow gap. The diffusivities of monolayers of TIP5P water between cristobalite walls reported by Zangi (D ≈ 4×10 −5 cm 2 /s), 85 and TIP3P water between (6,6) carbon nanotube membranes reported by Kalra et al 108 (D ≈ 2×10 −5 cm 2 /s), are approximately 2-5 times greater than the values calculated in this work, illustrat-ing the sensitivity of these results to the precise details of the system, and geometry of the gap. 34…”

Section: Monolayer Liquidmentioning

confidence: 94%

A computational investigation of the phase behavior and capillary sublimation of water confined between nanoscale hydrophobic plates

Ferguson

Giovambattista

Rossky

et al. 2012

The Journal of Chemical Physics

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Thin films of water under nanoscopic confinement are prevalent in natural and manufactured materials. To investigate the equilibrium and dynamic behavior of water in such environments, we perform molecular dynamics simulations of water confined between atomistically detailed hydrophobic plates at T = 298 K for pressures (-0.1) ≤ P ≤ 1.0 GPa and plate separations of 0.40 ≤ d ≤ 0.80 nm. From these simulations, we construct an expanded P-d phase diagram for confined water, and identify and characterize a previously unreported confined monolayer ice morphology. We also study the decompression-induced sublimation of bilayer ice in a d = 0.6 nm slit, employing principal component analysis to synthesize low-dimensional embeddings of the drying trajectories and develop insight into the sublimation mechanism. Drying is observed to proceed by the nucleation of a bridging vapor cavity at one corner of the crystalline slab, followed by expansion of the cavity along two edges of the plates, and the subsequent recession of the remaining promontory of bilayer crystal into the bulk fluid. Our findings have implications for the understanding of diverse phenomena in materials science, nanofluidics, and protein folding and aggregation.

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In addition, the hydrophobic effect is crucial to understanding the nature of surface friction in nanoscale fluid transport. [19][20][21][22][23][24] Surface friction characterizes the boundary condition in the continuum description for fluid flow across interfaces of varying hydrophobicity.…”

Section: Introductionmentioning

confidence: 99%

“…if the coordinate system is defined such that one direction is parallel and two directions are perpendicular to the line of centers. The two spheres are identical so by symmetry ζ 11 (r) = ζ 22 (r) and ζ 12 (r) = ζ 21 (r). The friction coefficient along the relative coordinate, r = r 2, − r 1, , may be obtained from manipulation of Eqn.…”

mentioning

confidence: 99%

Interplay between Hydrodynamics and the Free Energy Surface in the Assembly of Nanoscale Hydrophobes

Morrone

Berne

2011

J. Phys. Chem. B

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Solvent plays an important role in the relative motion of nanoscopic bodies, and the study of such phenomena can help elucidate the mechanism of hydrophobic assembly, as well as the influence of solvent-mediated effects on in vivo motion in crowded cellular environments. Here we study important aspects of this problem within the framework of Brownian dynamics. We compute the free energy surface that the Brownian particles experience and their hydrodynamic interactions from molecular dynamics simulations in explicit solvent. We find that molecular scale effects dominate at short distances, thus giving rise to deviations from the predictions of continuum hydrodynamic theory. Drying phenomena, solvent layering, and fluctuations engender distinct signatures of the molecular scale. The rate of assembly in the diffusion-controlled limit is found to decrease from molecular scale hydrodynamic interactions, in opposition to the free energy driving force for hydrophobic assembly, and act to reinforce the influence of the free energy surface on the association of more hydrophilic bodies.

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Lubrication by molecularly thin water films confined between nanostructured membranes

Cited by 11 publications

References 32 publications

Liquid water can slip on a hydrophilic surface

Liquid water can slip on a hydrophilic surface

A computational investigation of the phase behavior and capillary sublimation of water confined between nanoscale hydrophobic plates

Interplay between Hydrodynamics and the Free Energy Surface in the Assembly of Nanoscale Hydrophobes

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