Search results for "Capillary condensation"
showing 10 items of 18 documents
The open metastable structure of a collapsible sand: fabric and bonding
2015
This paper deals with the compositional and textural characteristics determining open metastable structures in the pleistocenic sand outcropping in the Agrigento district (Sicily). The aim of the study was to individuate the bonding types occurring between grains that could generate matric suction phenomena. The composition and microfabric were characterised by means of granulometry, porosimetry, permeability, optical and ESEM-EDS microscopy, thermogravimetry and XR diffractometry, electric conductivity, and ionic chromatography. The data thus acquired show that the skeleton of the sand is constituted mostly by bioclasts and microfossils, calcite and quartz monocrystalline grains. Moreover,…
Finite Size Effects in Thin Film Simulations
2003
Phase transitions in thin films are discussed, with an emphasis on Ising-type systems (liquid-gas transition in slit-like pores, unmixing transition in thin films, orderdisorder transitions on thin magnetic films, etc.) The typical simulation geometry then is a L xL x D system, where at the low confining L x L surfaces appropriate boundary “fields” are applied, while in the lateral directions periodic boundary conditions are used. In the z-direction normal to the film, the order parameter always is inhomogeneous, due to the boundary “fields” at the confining surfaces. When one varies the temperature T from the region of the bulk disordered phase to a temperature below the critical temperatu…
Real-time microfluorescence studies of Langmuir-Blodgett deposition: Monolayer adsorption and desorption
1990
Abstract Observations of the meniscus region in a typical Langmuir-Blodgett configuration are obtained using fluorescence microscopy. Studies of the meniscus position as a function of pH demonstrate that the meniscus height increases upon charging the monolayer owing to the repulsive interaction between monolayer and substrate surfaces. Through the correspondence between meniscus height and contact angle the adhesion forces between monolayer and substrate as a function of monolayer charge are assessed. The phenomenon of desorption upon resubmerging a deposited film is described and it is shown that the meniscus height at the onset of the desorption is greater for higher pH.
Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption
1998
Methods of nonlocal density functional theory (NLDFT), proposed recently for predictions of adsorption equilibrium and calculations of pore size distributions in micro- and mesoporous materials, were tested on reference MCM-41 materials. Five newly synthesized MCM-41 adsorbents with presumably uniform pore channels varying from 32 to 45 Å were characterized by X-ray diffraction (XRD), nitrogen adsorption at 77 K, and argon adsorption at 77 and 87 K. New sets of intermolecular interaction parameters of the NLDFT model for N2 and Ar adsorption on MCM-41 were determined. The parameters were specified to reproduce the bulk liquid-gas equilibrium densities and pressures, liquid-gas interfacial t…
Phase diagram of polymer blends in confined geometry
2001
Within self-consistent field theory we study the phase behavior of a symmetrical binary AB polymer blend confined into a thin film. The film surfaces interact with the monomers via short range potentials. One surface attracts the A component and the corresponding smei-infinite system exhibits a first order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmetric surfaces fields to the interface localization/delocalization transition for antisymmetric surface fields. In the former case the phase diagram has a single critical point close to the bulk critical point. In the latter case the phase diagram exh…
Colloid-polymer mixtures between asymmetric walls: Evidence for an interface localization transition
2007
We demonstrate via computer simulation that mixtures of colloids and polymers confined to thin films have the ability to undergo an interface localization transition. While one wall of the film is assumed to be hard for both particles, at the other wall, an additional repulsive potential acts, but on the colloids only. By varying the strength of this repulsion, a crossover from capillary condensation to interface localization is found. The latter occurs under conditions where in the bulk almost complete phase separation has occurred.
Water Sorption on Mesoporous Aluminosilicate MCM-41
1995
Characterization of the interaction of water with the highly ordered mesoporous solid MCM-41 (pore diameter ∼2.5 nm) is undertaken with the aid of several techniques (adsorption gravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and controlled rate-evolved gas analysis). The relatively complex water-MCM-41 interactions are characterized by a type V isotherm indicating an initial repulsive character followed by a capillary condensation step of the adsorbate. This highlights both hydrophobic and hydrophilic properties of this potential model mesoporous adsorbent.
Molecular mechanism of capillary condensation of acetonitrile vapor on MCM-41 with the aid of a time-correlation function analysis of IR spectroscopy
1998
Abstract The adsorption isotherm and IR spectra of acetonitrile adsorbed on MCM-41 (pore-width=3.2 nm) were measured at 303 K. The adsorption isotherm had a sharp jump at P / P 0 =0.3 without adsorption hysteresis. The CN stretching ν 2 -band of adsorbed acetonitrile had two-component α- and β-bands at 2263 and 2254 cm −1 , respectively, assigned to hydrogen-bonded molecules on surface hydroxyls of MCM-41 and physisorbed molecules in mesopores whose walls are coated with hydrogen-bonded molecules, respectively. The β-band was analyzed with a time correlation function, giving a reorientation time τ . The τ value of the adsorbed molecule before capillary condensation was smaller than that of …
Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)
2011
This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed…
Capillary condensation in the two-dimensional lattice gas: A Monte Carlo test of fluctuation corrections to the Kelvin equation
1997
A two-dimensional lattice gas model with nearest-neighbour attractive interaction confined in a strip of width L between two parallel boundaries at which an attractive short-range force acts is studied by Monte Carlo simulations, for cases where the system is in the wet phase near the critical wetting transition line for . We study the shift of the chemical potential of the transition in the strip as a function of L by thermodynamic integration methods, , and also obtain the thickness of the wetting film at the chemical potential at which capillary condensation occurs. In the range the data are consistent with a variation according to the Kelvin equation, , as well as with a shifted Kelvin …