Direct observation of surface effects on the freezing and melting of an n-alkane

Maeda, Nobuo; Christenson, Hugo K.

doi:10.1016/s0927-7757(99)00169-7

Cited by 32 publications

(59 citation statements)

References 33 publications

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“…The nonlinearity of the video screen was calibrated by using the two standard emission lines of a mercury lamp (Pen-Ray lamp 90-0012-01, Ultraviolet Products, San Gabriel, CA). The volume of a given condensate was calculated by using the formula V ϭ Rh 2 (10), where h is the measured surface separation at the liquid-vapor interface of the condensed liquid when the surfaces are in contact. In our geometry, the mean radius of curvature r of the liquid-vapor interface of a condensed liquid bridge is related to h by h ϭ 2rcos .…”

Section: Methodsmentioning

confidence: 99%

Evaporation and instabilities of microscopic capillary bridges

Maeda

Israelachvili

Kohonen

2003

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

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128

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: Methodsmentioning

confidence: 99%

Evaporation and instabilities of microscopic capillary bridges

Maeda

Israelachvili

Kohonen

2003

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

Self Cite

128

113

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“…A solute in the capillary condensate would give an additional lowering of the vapour pressure of the water in addition to that caused by the interfacial curvature. The volume of the condensate varies as its radius squared [121], while the area in contact with the condensate is proportional to r [121], so if solute that is uniformly distributed over the two mica surfaces dissolves in the condensate, the concentration and the activity aw for dilute solutions should decrease as 1/r. The adhesion force between the mica surfaces was not measurably affected by the presence of solute in the condensates, but was within the experimental error of a few percent equal to that expected for pure water condensates.…”

Section: Mica and The Surface Force Apparatusmentioning

confidence: 99%

The nature of the air-cleaved mica surface

Christenson

Thomson

2016

Surface Science Reports

107

102

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The accepted image of muscovite mica is that of an inert and atomically smooth surface, easily prepared by cleavage in an ambient atmosphere. Consequently, mica is extensively used a model substrate in many fundamental studies of surface phenomena and as a substrate for AFM imaging of biomolecules. In this review we present evidence from the literature that the above picture is not quite correct. The mica used in experimental work is almost invariably cleaved in laboratory air, where a reaction between the mica surface, atmospheric CO2 and water occurs immediately after cleavage. The evidence suggests very strongly that as a result the mica surface becomes covered by up to one formula unit of K2CO3 per nm 2 , which is mobile under humid conditions, and crystallizes under drier conditions. The properties of mica in air or water vapour cannot be fully understood without reference to the surface K2CO3, and many studies of the structure of adsorbed water on mica surfaces may need to be revisited. With this new insight, however, the air-cleaved mica should provide exciting opportunities to study phenomena such as two-dimensional ion diffusion, electrolyte effects on surface conductivity, and two-dimensional crystal nucleation.

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“…It may be speculated that the redistribution of stearic acid was at least partly due to capillary melting in the narrow slit between the PDMS and the silica, which is the result of a depression of the melting point due to wetting of the surfaces of the liquid stearic acid in preference to the solid. This is demonstrated to occur for n-octadecane confined between mica surfaces in a surface force apparatus by Maeda and Christenson [55].…”

Section: A Model Substance For "Contamination" By Wood Extractivesmentioning

confidence: 89%