On the Hydrogen Bonding Structure at the Aqueous Interface of Ammonium-Substituted Mica: A Molecular Dynamics Simulation

Abstract

Dedicated to Professor Alfred Klemm on the occasion of his 100th birthday.Molecular dynamics (MD) computer simulations were performed for an aqueous film of 3 nm thickness adsorbed at the (001) surface of ammonium-substituted muscovite mica. The results provide a detailed picture of the near-surface structure and topological characteristics of the interfacial hydrogen bonding network. The effects of deuterium/hydrogen isotopic substitution in N(H/D) 4 + on the dynamics and consequently on the convergence of the structural properties have also been explored. Unlike many earlier simulations, a much larger surface area representing 72 crystallographic unit cells was used, which allowed for a more realistic representation of the substrate surface with a more disordered distribution of aluminium/silicon isomorphic substitutions in muscovite. The results clearly demonstrate that under ambient conditions both interfacial ammonium ions and the very first layer of water molecules are H-bonded only to the basal surface of muscovite, but do not form H-bonds with each other. As the distance from the surface increases, the H-bonds donated to the surface by both N(H/D) 4 + and H 2 O are gradually replaced by the H-bonds to the neighbouring water molecules, with the ammonia ions experiencing one reorientational transition region, while the H 2 O molecules experiencing three such distinct consecutive transitions. The hydrated N(H/D) 4 + ions adsorb almost exclusively as inner-sphere surface complexes with the preferential coordination to the basal bridging oxygen atoms surrounding the aluminium/silicon substitutions.

Structure, Energetics, and Dynamics of Cs+ and H2O in Hectorite: Molecular Dynamics Simulations with an Unconstrained Substrate Surface

“…[99][100][101] The methods of analysis used here have been previously described in detail. 39,42,50,73 Results and Discussion…”

“…This water film is sufficiently thick to characterize both the interfacial features of the structure and the bulk-water behavior in the nano-pores, as demonstrated in previous simulation studies. 39,42,58 Molecular Dynamics (MD) simulations using the statistical NPT (constant N number of atoms, constant pressure P and constant Temperature T) and NVT (constant N number of atoms, constant volume V and constant Temperature T) ensembles were performed using the LAMMPS simulation code. 87 A Nosé-Hoover thermostat and barostat were used to control the temperature and the pressure independently in all 3 dimensions.…”

“…Though other H-bond definitions are possible, 95,96 23,39,42 For the purpose of H-bonding calculations, the oxygen atoms of the basal clay surface (Ob) were treated in the same way as OH2O (i.e., as potential H-bond acceptors). The origin for analysis of the atomic density profiles was the mean position of the surface Ob atoms.…”

“…Thus, the PADDs of OH2O coordinating Cs + shown in Figure 6a are not located in the same plane as the Cs + (z ≤2.5 Å) but at z > 3 Å with their HH2O pointing towards and away from the hectorite surface at z = 6 Å (see Figures S2 and S3 molecules is similar to their arrangements in previous simulations using mica. 110 Such arrangements occur because they allow H2O molecules to form more and stronger H-bonds among themselves than they would otherwise have. Two important points support the computed structural arrangement.…”

Competitive Adsorption of H2O and CO2 in 2-Dimensional Nanoconfinement: GCMD Simulations of Cs- and Ca-Hectorites

“…Recent experimental and computational modeling studies have clearly shown that the clay swelling behavior depends strongly on the nature of the charge balancing cation (characterized by the CO2 and H2O solvation energies) and on the composition and location of the permanent structural charge of the clay. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] Experimental and computational modeling studies have shown that at reservoir conditions the amount of intercalated CO2 and its structural, dynamical, and energetic properties depend on the basal spacing and the solvation energies of the charge-balancing cation with H2O and CO2 in smectite interlayers under supercritical conditions (scCO2, Tc~31ºC, Pc~73 bar). X-ray diffraction (XRD) studies at pressurized CO2 conditions by Giesting et al 18,19 showed that increase (expansion) of the basal spacing of the common smectite, montmorillonite, depends on the initial interlayer H2O content.…”