Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 2. Toward a Precise Coupling between Molecular Simulations and Diffraction Data

Abstract

International audienceA specific methodology was developed to collate the interlayer configurations resulting from Grand-Canonical Monte Carlo (GCMC) simulations with experimental X-ray and neutron diffraction data for two synthetic Na-saturated saponites having contrasting layer charge. Numerical simulations were performed assuming different existing sets of atomic partial charge and Lennard-Jones parameters for clay and water. For each parameter set and for the two samples in both the mono- and bihydrated states, the water contents resulting from GCMC simulations were first compared to water vapor desorption gravimetry data. The density distributions of interlayer species were then used to generate 00l intensities that were compared to X-ray and neutron diffraction data, the latter being recorded on both hydrogenated and deuterated specimens. The CLAYFF model [Cygan et al. J. Phys. Chem. B2004, 108, 1255] is shown to better account for water content and organization compared to the model developed by Skipper et al. (Clays Clay Miner.1995, 43, 285) and modified by Smith (Langmuir1998, 14, 5959). However, diffraction patterns calculated for bihydrated samples from CLAYFF simulations did not match satisfactorily the diffraction data. Lennard-Jones parameters were thus modified for oxygen atoms from the clay layer. When combined with the SPC/E water model, this modified version of CLAYFF allows matching experimental water contents and fitting the complete set of diffraction data. Relevant information may thus be derived on the influence of layer charge on the orientational properties of interlayer water molecules which differs for the different clay models. Finally, the approach used in the present study proved powerful for assessing atomic interaction parameters considered for computational simulations

Molecular Dynamics Simulations of Anion Exclusion in Clay Interlayer Nanopores

“…Mg isomorphic substitution was assigned to the site of substitution and its six surrounding O atoms in accordance with the original CLAYFF model. The treatment of clay mineral negative structural charge used in the present study was derived from quantum mechanical calculations of the electrostatic potential near clay mineral surfaces (Cygan et al, 2004), which predicts interlayer water and ion distributions and dynamics in excellent agreement with experimental results (Bourg and Sposito, 2010;Ferrage et al, 2011;Marry et al, 2011). The present results do not allow an accurate quantification of the height of the energy barrier opposing Cl À entry into the interlayer space of the 2WL hydrate, but strongly suggest that this barrier is greater than that predicted by Hsiao and Hedstrom (2015).…”

Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites

“…12,13,30,31 Since only a limited number of similar organic/water/clay studies have previously been reported, finding and implementing a self-consistent set of force-fields for organic/water/clay is not trivial. In this study, a topology built from α-lactose with the charmmgui server and the ch2lmp LAMMPS tool was used with the CHARMM36 all-atom carbohydrate force-field to describe the lactose molecules.…”

Intercalação de íons em nanossilicatos

“…(1), for a given RH are related to the hydration state, which depends on the type of interlayer cation. As reported in several previous publications(da Ferrage et al, 2010;Ferrage et al, 2005;Ferrage et al, 2011;Gates et al, 2012), for Na + the stable hydration states correspond to zero water layer (0WL) (dehydrated peak), one water layer (1WL) and two water layers (2WL). For the case of Li + as interlayer cation (Tenorio et al, 2010), the stable hydration states are 0WL, 1WL, one-and-a-half WL (1.5 WL) and 2WL.…”

“…It was also observed that the environmental history of the clay samples is important for the detailed behavior displayed by these isotherms. In addition, based on thermogravimetric and differential scanning calorimetry measurements, a complete Ni-fluorohectorite dehydrated state only can be reached at long (several hours) isotherm times at 70 °C, or at shorter times ( , 2010;Ferrage et al, 2005;Ferrage et al, 2011;Oueslati et al, 2011;Tenorio et al, 2010), NMR (Fleury et al, 2013;Tenorio et al, 2008;Tenorio et al, 2010) and molecular dynamics simulations (Ebrahimi et al, 2014;Skipper et al, 1991a;Tambach et al, 2004;Zheng and Zaoui, 2011).Synthetic clay minerals have the advantage that they possess a more homogeneous charge distribution, and also contain significantly fewer impurities (e.g. carbonates, (hydr)oxides, silica, and organic matter) than their natural counterparts (Bergaya and Lagaly, 2013).…”