Layer critical points of multilayer ethane adsorbed on graphite

Nham, H. S.; Hess, G. B.

doi:10.1103/physrevb.38.5166

Cited by 23 publications

(5 citation statements)

References 22 publications

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“…Other gases that have been shown to have complex layering adsorption phase diagrams are ethylene [175,345], ethane [256] and xenon and krypton [395]; much of the work in this area has been concisely reviewed [143].…”

Section: Methodsmentioning

confidence: 99%

Phase separation in confined systems

et al. 1999

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We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas-liquid (capillary condensation), layering, liquid-liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid-liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

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Section: Methodsmentioning

confidence: 99%

Phase separation in confined systems

et al. 1999

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“…There is a growing amount of experimental evidence, for gases adsorbed on graphite, that transitions between layered liquid films do take place for T > Ttr. Ethylene [52,53], ethane [54] and oxygen [55] are cases, see figure 7, where up to seven or eight discrete steps in the adsorption have been resolved in ellipsometric measurements or heat-capacity studies. Note that the criticality of layering transitions should also lie in the d = 2 Ising universality class.…”

Section: Other Phase Transitionsmentioning

confidence: 99%

Liquids at interfaces: what can a theorist contribute?

Evans¹,

Parry²

1990

J. Phys.: Condens. Matter

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Reviews some recent theoretical and computer simulation studies of simple atomic fluids adsorbed at structureless substrates. Emphasis is placed on phase transitions, especially the various types of wetting transition. Criticality is associated with capillary-wave-like fluctuations in a continuously growing wetting film. This is of a subtle nature, which is best understood in terms of the pairwise correlation function of the fluid. Other surface phase transitions, such as prewetting and layering, occur out of bulk coexistence. Theory suggests that for sufficiently attractive substrates a sequence of first-order transitions, corresponding to the growth of new adsorbed liquid layers, should occur as the pressure of the bulk gas increases towards saturation at temperatures not too far above the bulk triple point. The extent to which such behaviour is found in adsorption experiments is discussed. The authors also argue that a simple fluid confined between two parallel hard-walls can exhibit surprisingly rich equilibria.

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“…The wetting behavior of fluid films of normal alkanes [ n -C n H 2 n +2 ] has been the subject of only a small number of investigations. In the case of shorter alkanes that are largely of fundamental interest, there have been detailed studies of multilayer ethane (C 2 H 6 ) films adsorbed on graphite to determine the layer condensation critical temperatures by the volumetric adsorption isotherm technique and by high-resolution ellipsometry . In the case of longer alkanes (15 ≤ n ≤ 50), which have greater technological interest, there have been studies of the wetting topologies of fluid films adsorbed on SiO 2 surfaces. − These alkanes are of sufficient length to exhibit the surface freezing effect at the bulk liquid/air interface .…”

Section: Introductionmentioning

confidence: 99%

Ellipsometric and Neutron Diffraction Study of Pentane Physisorbed on Graphite

et al. 2005

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High-resolution ellipsometry and neutron diffraction measurements have been used to investigate the structure, growth, and wetting behavior of fluid pentane (n-C(5)H(12)) films adsorbed on graphite substrates. We present isotherms of the thickness of pentane films adsorbed on the basal-plane surfaces of a pyrolytic graphite substrate as a function of the vapor pressure. These isotherms are measured ellipsometrically for temperatures between 130 and 190 K. We also describe neutron diffraction measurements in the temperature range 11-140 K on a deuterated pentane (n-C(5)D(12)) monolayer adsorbed on an exfoliated graphite substrate. Below a temperature of 99 K, the diffraction patterns are consistent with a rectangular centered structure. Above the pentane triple point at 143.5 K, the ellipsometric measurements indicate layer-by-layer adsorption of at least seven fluid pentane layers, each having the same optical thickness. Analysis of the neutron diffraction pattern of a pentane monolayer at a temperature of 130 K is consistent with small clusters having a rectangular-centered structure and an area per molecule of approximately 37 A(2) in coexistence with a fluid monolayer phase. Assuming values of the polarizability tensor from the literature and that the monolayer fluid has the same areal density as that inferred for the coexisting clusters, we calculate an optical thickness of the fluid pentane layers in reasonable agreement with that measured by ellipsometry. We discuss how these results support the previously proposed "footprint reduction" mechanism of alkane monolayer melting. In the hypercritical regime, we show that the layering behavior is consistent with the two-dimensional Ising model and determine the critical temperatures for layers n = 2-5.

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Layer critical points of multilayer ethane adsorbed on graphite

Cited by 23 publications

References 22 publications

Phase separation in confined systems

Phase separation in confined systems

Liquids at interfaces: what can a theorist contribute?

Ellipsometric and Neutron Diffraction Study of Pentane Physisorbed on Graphite

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