Susana Figueroa-Gerstenmaier

Storage of hydrogen as a guest of a nanoporous polymeric crystalline phase

A mechanism of H(2) uptake, based on adsorption in the ordered cavities of nanoporous polymeric crystalline phases rather than on disordered amorphous polymeric surfaces, has been clearly established, for aerogels of syndiotactic polystyrene (s-PS) exhibiting the nanoporous δ phase. An ordered arrangement of the H(2) molecules is proven by FTIR spectra while the inclusion of H(2) is assessed by gravimetric measurements and molecular simulations.

Application of the fundamental measure density functional theory to the adsorption in cylindrical pores

In this work we have implemented the fundamental-measure density functional theory due to Kierlik and Rosinberg to describe the adsorption of Lennard-Jones molecules in cylindrical pores. The accuracy of the theory in predicting adsorption isotherms and particle density profiles is checked by comparison with grand canonical Monte Carlo simulations for a wide range of pore sizes, showing very good agreement in all cases. In addition, the theory has been applied to the adsorption in slitlike pores to study the influence of the pore geometry on this property. The results indicate that the confinement of the cylindrical geometry introduces significant differences in the shape of the adsorption isotherms and density profiles. These differences are relevant for the characterization of porous materials.

Theoretical modelling of adsorption of hydrogen onto graphene, MOFs and other carbon-based substrates

Adsorption of molecular hydrogen () onto graphene and other carbon-based substrates is currently a research area of interest, where molecular-based approaches are required to describe thermodynamic properties of this and other related systems. We present a semiclassical theoretical framework to model adsorption isotherms of quantum fluids such as , based on the statistical associating fluid theory for chain molecules interacting with potentials of variable range for classical and quantum bulk fluids (SAFT-VRQ), and its extension to describe adsorbed systems (SAFT-VR-2D). Although the application of the theory relies on the determination of eight molecular parameters, seven of them can be obtained from bulk thermodynamic properties, the ratio of the critical temperatures of the adsorbed and bulk phases, and theoretical estimations about the range of the surface-particles potential and the energy depth of the particle–particle potential of the adsorbed fluid. The energy depth of the surface-particle potential, εw, is the free molecular parameter that can be obtained by fitting to experimental data of adsorption isotherms. Results obtained for εw according to this procedure are consistent with experimental values of the isosteric heat and the prediction of adsorption isotherms is in very good agreement with the experimental data.

Colloid-polymer mixtures under slit confinement

We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1⩾q⩾0.4 and the confinement distance, H, in 10σc⩾H⩾3σc, σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc)-1 for H≳4σc. The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc)-1, from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.

Characterization of Semicrystalline Polymeric Materials by Atomistic Models

Characterization of two crystalline phases (δ and e) of syndiotactic polystyrene using molecular modeling are discussed. These two polymorphs present nanoporosity, being able to adsorb molecules of low molecular weight in their cavities (δ) or in their channels (e). By means of Grand Canonical Monte Carlo molecular simulations, adsorption isotherms of nitrogen and hydrogen were calculated, exploring the possible utilization of these materials with storage purposes. Molecular Dynamics simulations were performed to determine self diffusion behavior of light gases and these results combined with a geometric method are being employed to measure the size of the nanochannels of the e polymorph.