Properties of Three Capillary Fluids in the Critical Region

Machin, William D.

doi:10.1021/la971393r

Cited by 42 publications

(48 citation statements)

References 23 publications

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“…An exception to the general trend is observed near the critical temperature and the critical density. At reduced density values between 0.9 and 1.2, the measured values of the excess amount adsorbed at 31.4 • C are in fact smaller than or equal to those at 36.3 • C. Similar effects have been observed previously for other experimental systems, and have been called "critical depletion" (Machin , 1999;Rajendran et al, 2002;Thommes et al, 1994Thommes et al, , 1995. Such phenomenon has always eluded a convincing theoretical explanation.…”

Section: Measurements Over a Wider Temperature Rangesupporting

confidence: 75%

“…Another phenomenon, called critical depletion, was presented for the first time by Findenegg and coworkers for the case of SF 6 on graphitized carbon black using a volumetric adsorption apparatus (Thommes et al, 1994). The phenomenon of critical depletion was then further confirmed by adsorption measurements of the same adsorbate on controlled pore glasses CPG-350 and CPG-100 (Machin , 1999). Several attempts to theoretically explain critical depletion have been proposed by the same authors.…”

Section: Introductionmentioning

confidence: 90%

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Reliable measurement of near-critical adsorption by gravimetric method

et al. 2006

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A gravimetric apparatus is used to measure the excess adsorption at high pressure. The equipment consists of a Rubotherm magnetic suspension balance, which allows to measure also the density of the fluid. In order to obtain the excess adsorbed amount, the measured weight has to be corrected with a buoyancy term, for which the density of the adsorbing fluid has to be known at each experimental conditions. Therefore the homogeneity of density in the high-pressure cell plays a fundamental role in determining the accuracy of the measured excess adsorbed amounts. This paper is intended to show the impact of the actual approach to thermostating the unit on the density distribution of the adsorbing fluid inside the high-pressure cell. Namely, by changing the inlet position of the heating fluid, large differences in the measured excess adsorption are produced. The closer to the critical point of the fluid, the R. Pini, S. Ottiger . A. Rajendran . M. Mazzotti ( ) ETH Zurich, Institute of Process Engineering,

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Section: Measurements Over a Wider Temperature Rangesupporting

confidence: 75%

Section: Introductionmentioning

confidence: 90%

Reliable measurement of near-critical adsorption by gravimetric method

et al. 2006

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“…The behavior of fluids in pores near the liquid-vapor critical point has often been discussed in terms of a "capillary critical point" but there are a variety of definitions of this point 12,13,35 . It is sometimes assumed to be the temperature where hysteresis disappears; in other work FIG.…”

Section: Discussionmentioning

confidence: 99%

“…Experimental work on capillary condensation of nearcritical fluids includes dense porous glasses such as CPG (controlled pore glass) 12,13,14 . These studies show a slight narrowing in the phase separation curve, with the "vapor" branch shifted to higher densities than in the bulk fluid.…”

Section: Introductionmentioning

confidence: 99%

Helium adsorption in silica aerogel near the liquid-vapor critical point

2005

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We have investigated the adsorption and desorption of helium near its liquid-vapor critical point in silica aerogels with porosities between 95% and 98%. We used a capacitive measurement technique which allowed us to probe the helium density inside the aerogel directly, even though the samples were surrounded by bulk helium. The aerogel's very low thermal conductivity resulted in long equilibration times so we monitored the pressure and the helium density, both inside the aerogel and in the surrounding bulk, and waited at each point until all had stabilized. Our measurements were made at temperatures far from the critical point, where a well defined liquid-vapor interface exists, and at temperatures up to the bulk critical point. Hysteresis between adsorption and desorption isotherms persisted to temperatures close to the liquid-vapor critical point and there was no sign of an equilibrium liquid-vapor transition once the hysteresis disappeared. Many features of our isotherms can be described in terms of capillary condensation, although this picture becomes less applicable as the liquid-vapor critical point is approached and it is unclear how it can be applied to aerogels, whose tenuous structure includes a wide range of length scales.

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“…[1][2][3]. The interplay of finite size and surface effects strongly modifies the phase behavior of such confined fluids [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in comparison with the bulk. The vapor to liquid transition is shifted ("capillary condensation"), as well as critical points [3,4,9,12].…”

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confidence: 99%

Rounding of Phase Transitions in Cylindrical Pores

et al. 2010

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Phase transitions of systems confined in long cylindrical pores (capillary condensation, wetting, crystallization, etc.) are intrinsically not sharply defined but rounded. The finite size of the cross section causes destruction of long range order along the pore axis by spontaneous nucleation of domain walls. This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted by a phenomenological theory. We show that characteristic differences between the behavior of pores of finite length and infinitely long pores occur. In pores of finite length a rounded transition occurs first, from phase coexistence between two states towards a multi-domain configuration. A second transition to the axially homogeneous phase follows near pore criticality. PACS numbers: 64.75Jk, 64.60.an, 05.70Fh, 02.70Tt Fluids and fluid mixtures in nano-and microporous materials (pore diameters from 1 nm to 150 nm) play important roles in various industries (extracting oil and gas from porous rocks; use as catalysts or for mixture separation in the chemical and pharmaceutical industry; nanofluidic devices, etc.) [1][2][3]. The interplay of finite size and surface effects strongly modifies the phase behavior of such confined fluids [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in comparison with the bulk. The vapor to liquid transition is shifted ("capillary condensation"), as well as critical points [3,4,9,12]. Effects of wetting [20] on phase coexistence give rise to interesting patterns (plugs versus capsules versus tube structures etc. [7]). However, although various phase diagrams (different from the bulk) have been proposed (e.g. [1,3,7,9,12,13,17]), many aspects hitherto are not well understood. E.g., the "critical point" where adsorption/desorption hysteresis vanishes seems to be systematically lower than the critical temperature where the density difference between the vapor-like and liquid-like states vanishes [12], in contrast to what theories have predicted [14].However, a crucial aspect (stressed only in a few pioneering studies [3,8], and in the context of Ising/lattice gas models [21][22][23]) is the rounding of all transitions, caused by the quasi-one-dimensional character of a fluid in a long cylindrical pore with cross-sectional radius R. With the current progress of producing pores of wellcontrolled diameter varying from the nanoscale (carbon nanotubes [23][24][25]) to arrays of pores in silicon wafers [26], up to 150 nm wide and of well-controlled length, experiments become feasible which are not plagued by effects of random disorder, which occur in porous glasses [1,27]. Thus, it is important to understand the phase transitions in pores more precisely, considering both the radius R and the length L of the pore as variables (the important role of L has so far been largely disregarded). In the present Letter, we elucidate the rounding of vaporliquid type transitions in cylindrical pores, based on Monte Carlo sim...

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Properties of Three Capillary Fluids in the Critical Region

Cited by 42 publications

References 23 publications

Reliable measurement of near-critical adsorption by gravimetric method

Reliable measurement of near-critical adsorption by gravimetric method

Helium adsorption in silica aerogel near the liquid-vapor critical point

Rounding of Phase Transitions in Cylindrical Pores

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