Capillary Condensation and Interface Structure of a Model Colloid-Polymer Mixture in a Porous Medium

We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, where the matrix particles are quenched and the colloids and polymers are annealed, i.e. allowed to equilibrate. We study capillary condensation of the mixture in a tiny sample of matrix as well as demixing and the fluid-fluid interface inside a bulk matrix. Density profiles normal to the interface and surface tensions are calculated and compared to the case without matrix. Two kinds of matrices are considered: (i) colloid-sized matrix particles at low packing fractions and (ii) large matrix particles at high packing fractions. These two cases show fundamentally different behavior and should both be experimentally realizable. Furthermore, we argue that capillary condensation of a colloidal suspension could be experimentally accessible. We find that in case (ii), even at high packing fractions, the main effect of the matrix is to exclude volume and, to high accuracy, the results can be mapped onto those of the same system without matrix via a simple rescaling.Comment: 12 pages, 9 figures, submitted to PR

Self-association and complex formation in alcohol-unsaturated hydrocarbon systems - Heat capacities of linear alcohols mixed with alkenes and alkynes

Apparent molar heat capacities, C-m(app),at dilute alcohol concentrations and excess molar heat capacities, C-p(E) throughout the concentration range were determined at 25 degrees C for the following systems: methanol, ethanol, propan-1-ol, hexan-1-ol and decan-1-ol mixed with n-octane, oct-1-ene and oct-1-yn

A molecular model for H2 interactions in aliphatic and aromatic hydrocarbons

A model for molecular hydrogen interacting with aliphatic and aromatic hydrocarbons is presented. The model has been derived using ab initio techniques and molecular dynamics simulations. In particular, quadrupole moments of hydrogen, and variation on energy with intermolecular distance of different conformations for the hydrogen-benzene couple were calculated using the Møller-Plesset method. Hydrogen was modelled using a two-centre Lennard-Jones potential plus electrostatic interactions. Lennard-Jones parameters were optimized on the basis of a correct reproduction of experimental data of hydrogen solubility in benzene and cyclohexane, calculated using the test particle insertion method. Different sets of parameters for specific interactions (hydrogen-aliphatic and hydrogen-aromatic systems) were considered avoiding the simple use of Lorentz-Berthelot combining rules. Additionally, structural and thermodynamic properties of hydrogen-benzene, hydrogen-cyclohexane and hydrogen in an equimolar mixture of benzene-cyclohexane at different low concentrations of hydrogen were investigated by means of molecular dynamics simulations. Electrostatic charges were taken from ab initio quantum mechanical calculations but after careful analysis of the calculated properties, their irrelevance was evidenced. Moreover, Coulombic interactions make simulations more expensive and, therefore, we do not recommend their inclusion in the modelling of hydrogen-aliphatic and aromatic interactions. © 2009 the Owner Societies

Application of Density Functional Theory for Determining Pore-Size Distributions of Microporous Activated Carbons

International audienceWe determined the pore-size distributions (PSDs) of 12 activated carbons (ACs) using a combination of density functional theory method from Kierlik and Rosinberg applied to slit-like pores and a regularization method. This combination of methods was applied to nitrogen adsorption isotherms at 77.35 K on the selected ACs, prepared by heat treatment of lignin impregnated with orthophosphoric acid. The effect of three variables, namely, activation temperature, orthophosphoric acid/lignin weight ratio and time of impregnation, was discussed with respect to the resultant PSDs

Hydrogen adsorption by delta and epsilon crystalline phases of syndiotactic polystirene aerogels

The H2 uptake from s-PS samples exhibiting different crystalline phases and different morphologies has been studied by gravimetric measurements at 77 K in the hydrogen pressure range from 0 up to 1.7 MPa and compared with molecular simulations relative to s-PS crystals. Gravimetric experiments show that the molecular hydrogen sorption is strongly dependent on the sample morphology and is maximum for low-density polymer aerogels. However, independently of the morphology, theH2 uptake is minimum for the dense \u3b2 and \u3b3 crystalline phases, intermediate for the channel-shaped nanoporous \u3b5 phase, and maximum for the cavity-shaped nanoporous \u3b4 phase. In particular, although the two nanoporous crystalline phases present essentially the same density (0.98 g/cm3), the hydrogen uptake from the \u3b4 phase is roughly double with respect to the uptake from the \u3b5 phase, both for powders and for aerogels. Infrared measurements and molecular simulations well agree with these quantitative sorption data and clearly indicate that, for both low and high pressure, the hydrogen molecules are preferentially adsorbed into the nanoporous crystalline phases. In particular, molecular simulations indicate that the maximum average hydrogen uptake is of nearly 3 molecules per cavity of the \u3b4 phase and of nearly 3.5 molecules per unit height of the channels of the \u3b5 phase