Structure, Dynamics, and Stability of Water Molecules during Interfacial Interaction with Clay Minerals: Strong Dependence on Surface Charges

Abstract

Water participates actively in a wide range of interfacial adsorption and reaction processes, and its structure, dynamics, and stability, all of which are crucial to these processes, have been addressed in the present study by means of molecular dynamics simulations. The structure and dynamic behaviors of interfacial water are distinct from those of bulk water and rely strongly on the amounts of surface charges in clay minerals; for example, H-bonds exist predominately among the interfacial water molecules for zero and low surface charges, whereas prevail between the water molecules and clay surfaces for high surface charges. Stabilities of the interfacial water molecules oscillate remarkably during an increase of surface charges that first decline and then are pronouncedly enhanced. Surface charges play a critical role during the interfacial clay/water interaction, and the interfacial water molecules are “liquid-like” at zero and low surface charges but “ice-like” at high surface charges. The present results greatly promote our understanding of clays/water interfaces that exist ubiquitously in environmental conditions.

Unraveling the Mechanism of Ice Nucleation by Mica (001) Surfaces

“…As mentioned above, this might be because the uniformity of the surface does not template two separated layers of water molecules necessary to form an ice-like bilayer. The lack of ice nucleation by the B-mica (all Si) surface is consistent with the surface charge density analysis of Li et al 66 We remark that a similar ice nucleation mechanism involving a mixed-phase nucleus was previously reported by our group for the Si-surface of kaolinite. 26 However, it was recently noticed that due to a program bug some of the Si atoms in the surface used in ref 26 were slightly displaced from their correct lattice positions.…”

“…As mentioned above, this might be because the uniformity of the surface does not template two separated layers of water molecules necessary to form an ice-like bilayer. The lack of ice nucleation by the B-mica (all Si) surface is consistent with the surface charge density analysis of Li et al…”

“…There are different ways to arrange the Si and Al atoms consistent with the Loewenstein rule that there be no Al–O–Al bonds . The Si/Al surface arrangement used in nearly all of our simulations is shown in Figure and has been widely used in earlier work. ,,,− Here the labels (B,H,K)-mica without further qualification refer to the Si/Al arrangement shown in Figure . This Si/Al arrangement was identified as a relatively stable structure in a density functional theory (DFT) study, and previous MD simulations at 300 K have suggested that water on the B-mica surface can have ice-like arrangements …”

“…The crystal is monoclinic with lattice parameters a = 5.199 Å, b = 9.027 Å, c = 20.106 Å, α = 90.0°, β = 95.782°, and γ = 90.0°. This crystal structure has been widely used for modeling mica in previous computational studies. ,,, Slabs of different dimensions were obtained by replicating the crystal structure (Figure S1) in the X , Y , and Z directions using the Visualization for Electronic and Structure Analysis (VESTA) software . VESTA was also employed for the measurement of distances between points in the crystal lattice.…”

“…This Si/Al arrangement was identified as a relatively stable structure in a density functional theory (DFT) study, 69 and previous MD simulations at 300 K have suggested that water on the B-mica surface can have icelike arrangements. 66 For comparison purposes, we carried out simulations for two additional Si/Al surface arrangements, in particular, a structure recently employed by Jin et al 7 (designated (B,H,K)-mica*) and another potentially stable structure reported in ref 69 (designated B-mica**). All three surface Si/Al arrangements are illustrated in Figure S2.…”