Molecular structure and dynamics of an aqueous sodium chloride solution in nano-pores between portlandite surfaces: a molecular dynamics study

Abstract

Portlandite plays an important role in the hydration phase of cement-based materials and influences the strength and durability of such materials. This study describes a molecular dynamics study of the structure and dynamics of water and ions confined at ambient temperature in calcium hydroxyl nanopores with widths of 35 Å. Strong layering of water in the vicinity of the (001) surface of portlandite demonstrates special structural features such as large density, good orientation preference, ordered interfacial organization and low diffusion rate. Due to the fixed vibration and rotation of the hydroxyl groups at the interface, water molecules within the first adsorbed layer adopt both H-downward and H-upward orientations by donating H-bonds and accepting H-bonds from the OH groups in the solid surface. Regarding the interaction of the ions and portlandite, Na(+) ions, deeply rooted in spaces in the surface hydroxyl groups, are significantly slowed and remain near the surface for long periods of time. On the other hand, due to the weak H-bonds formed by chloride ions and hydroxyl groups, adsorbed chloride ions near the surface cannot remain for longer times. In addition, when water and ions are confined in the nano-pores, the residence time for the ion-water and ion-ion clusters is lengthened so that the ion adsorption capability of the porlandite surface is enhanced due to the stable Na-Cl connections in the electrolyte solution.

The Impact of Salinity on the Interfacial Structuring of an Aromatic Acid at the Calcite/Brine Interface: An Atomistic View on Low Salinity Effect

“…54,55 The literature also confirms the second peak at 5.2 Å for the bulk space, which belongs to solvent-separated ion pairs. 55,56 As shown in Figure 5, it is more probable to observe Na + −Cl − pairs in the bulk SW, whereas in the interface of LS, that type of ion pairing is more plausible. The RDF between benzoates and water reflects the strong interaction between these molecules, indicated by the formation of multiple hydration shells around benzoates ( Figure S4).…”

Water properties under nano-scale confinement

“…Takei et al . 2000 postulate that the decrease in water density can be attributed to a decrease in the CN toward CN = 4, similar to ice, from CN = 4.4, as seen in bulk water 7,31 . Similar conclusions have been made by Iiayama et al .…”

Mineral- and Ion-Specific Effects at Clay–Water Interfaces: Structure, Diffusion, and Hydrodynamics

“…6 They also provide molecular scale information on the local viscosity of the confined fluid [7][8][9][10] as well as the relevant boundary conditions (stick or slip) which should be applied for a given interface, depending on the nature of both the solid wall and the confined fluid, with the quantification of the slip length [11][12][13] and its correlation with other properties such as the contact angle. 14 Due to their importance in the above-mentioned geological applications, the dynamics of fluids in nanopores of clay and related natural minerals [15][16][17][18][19][20] have attracted a lot of attention from the experimental and modelling point of view. We will not discuss here the interlayer pores, where only 1 or 2 fluid layers are present (see e.g.…”