Kinetics of Capillary Condensation in a Nanoscale Pore

Kohonen, Mika M.; Maeda, Nobuo; Christenson, HK

doi:10.1103/physrevlett.82.4667

Cited by 107 publications

(129 citation statements)

References 19 publications

(18 reference statements)

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“…This feature did not allow accurate measurements of their refractive index profiles, and, therefore, we concentrated here instead on the mean refractive index of the n-hexadecane bridges. This effect may be related to the large difference in the rates of evaporation of the two liquids (12)(13)(14)(15). Second, the much slower rates of evaporation and condensation of n-hexadecane allowed for more accurate measurements to be made, especially during the final stages of evaporation, than was previously possible with cyclohexane.…”

Section: Resultsmentioning

confidence: 99%

Evaporation and instabilities of microscopic capillary bridges

Maeda

Israelachvili

Kohonen

2003

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

129

113

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The formation and disappearance of liquid bridges between two surfaces can occur either through equilibrium or nonequilibrium processes. In the first instance, the bridge molecules are in thermodynamic equilibrium with the surrounding vapor medium. In the second, chemical potential gradients result in material transfer; mechanical instabilities, because of van der Waals force jumps on approach or a Rayleigh instability on rapid separation, may trigger irreversible film coalescence or bridge snapping. We have studied the growth and disappearance mechanisms of laterally microscopic liquid bridges of three hydrocarbon liquids in slit-like pores. At rapid slit-opening rates, the bridges rupture by means of a mechanical instability described by the Young-Laplace equation. Noncontinuum but apparently reversible behavior is observed when a bridge is held at nanoscopic surface separations H close to the thermodynamic equilibrium Kelvin length, 2r Kcos , where rK is the Kelvin radius and is the contact angle. During the course of slow evaporation (at H > 2r Kcos ) and subsequent regrowth by capillary condensation (at H < 2r Kcos ), the refractive index of the bridge may vary continuously and reversibly between that of the bulk liquid and vapor. The evaporation process becomes irreversible only at the very final stage of evaporation, when the refractive index of the fluid attains virtually that of the vapor. Measured refractive index profiles and the time-dependence of evaporating neck diameters also seem to differ from predictions based on a continuum picture of bridge evaporation far from the critical point. We discuss these findings in terms of the probable density profiles in evolving liquid bridges.T he equilibrium and dynamic aspects of phase changes are often influenced by the presence of surfaces and interfaces. For example, in the case of homogeneous nucleation of a liquid phase, a significant supersaturation must be reached before vapor starts to condense to form droplets because of the activation barrier in the free energy that hinders the nucleation of clusters smaller than a certain size. Interfaces can lower this activation barrier and speed up the nucleation process. From a practical point of view, the nucleation, condensation, and evaporation of fluids in confined geometries play a major role in adhesion, the behavior of moist granular materials, and the transport of fluids through porous media.Much less attention has been paid to the process of evaporation or disappearance of capillary-held liquids than to their formation (condensation or nucleation). The surface force apparatus (SFA; refs. 1-3) provides a powerful means with which to study the behavior of highly confined fluids and has been used to study various aspects of capillary condensed liquids. Recently, we reported some preliminary results on the evaporation of microscopic cyclohexane bridges (4). The major result from this study was the observation of lateral refractive index gradients across the evaporating bridges once they shrink below a cert...

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Section: Resultsmentioning

confidence: 99%

Evaporation and instabilities of microscopic capillary bridges

Maeda

Israelachvili

Kohonen

2003

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

129

113

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“…9 For a long time a very simple equation deduced from their theories has been used to describe the capillary force, F c , between an ideally smooth spherical tip of radius R T and a flat surface: 1,[10][11][12] where γ is the liquid tension and θ T and θ S are the contact angles of the tip and the flat surface, respectively. However, several discrepancies have been found between experiments and eq 1.…”

Section: Introductionmentioning

confidence: 99%

The ²/₃ Power Law Dependence of Capillary Force on Normal Load in Nanoscopic Friction

et al. 2004

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During the sliding of an atomic force microscope (AFM) tip on a rough hydrophilic surface, water capillary bridges form between the tip and the asperities of the sample surface. These water bridges give rise to capillary and friction forces. We show that the capillary force increases with the normal load following a 2 / 3 power law. We trace back this behavior to the load induced change of the tip-surface contact area which determines the number of asperities where the bridges can form. An analytical relationship is derived which fully explains the observed interplay between humidity, velocity, and normal load in nanoscopic friction.

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“…Twophase flows in micro-and nano-pores would require understanding of flows and interactions between nano-sized droplets. One recent example of this situation is provided by the surface force apparatus studies of capillary condensation in a nanoscale pore [7]. Droplets, bubbles, and grains of various sizes may move at various characteristic speeds.…”

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confidence: 99%

Motion of grains, droplets, and bubbles in fluid-filled nanopores

Sushko

Cieplak

2001

Phys. Rev. E

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Molecular dynamics studies of nono-sized rigid grains, droplets and bubbles in nano-sized pores indicate that the drag force may have a hydrodynamic form if the moving object is dense and small compared to the pore diameter. Otherwise, the behavior is non-hydrodynamic. The terminal speed is insensitive to whether the falling droplet is made of liquid or a solid. The velocity profiles within droplets and bubbles that move in the pore are usually non-parabolic and distinct from those corresponding to individual fluids. The density profiles indicate motional shape distortion of the moving objects.

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Kinetics of Capillary Condensation in a Nanoscale Pore

Cited by 107 publications

References 19 publications

Evaporation and instabilities of microscopic capillary bridges

Evaporation and instabilities of microscopic capillary bridges

The ²/₃ Power Law Dependence of Capillary Force on Normal Load in Nanoscopic Friction

Motion of grains, droplets, and bubbles in fluid-filled nanopores

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Kinetics of Capillary Condensation in a Nanoscale Pore

Cited by 107 publications

References 19 publications

Evaporation and instabilities of microscopic capillary bridges

Evaporation and instabilities of microscopic capillary bridges

The 2/3 Power Law Dependence of Capillary Force on Normal Load in Nanoscopic Friction

Motion of grains, droplets, and bubbles in fluid-filled nanopores

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The ²/₃ Power Law Dependence of Capillary Force on Normal Load in Nanoscopic Friction