Fresh Molecular Look at Calcite-Brine Nanoconfined Interfaces

Abstract

Calcite-fluid interface plays a central role in geochemical, synthetic, and biological crystal growth. The ionic nature of the calcite surface can modify the fluid-solid interaction and the fluid properties under spatial confinement and can also influence the adsorption of chemical species. We investigate the structure of the solvent and ions (Na, Cl, and Ca) at the calcite-aqueous solution interface under confinement and how such environment modifies the properties of water. To properly investigate the system, molecular dynamics simulations were employed to analyze the hydrogen bond network and to calculate NMR relaxation times. Here, we provide a new insight with additional atomistically detailed analysis by relating the topology of the hydrogen bond network with the dynamical properties in nanoconfinement interfaces. We have shown that the strong geometrical constraints and the presence of ions do influence the hydrogen bond network, resulting in more extended geodesic paths. Hydrogen bond branches connect low to high dynamics molecules across the pore and hence may explain the gluelike mechanical properties observed in the confinement environment. Moreover, we showed that the surface water observed at the calcite interface is characterized by slow transversal spin relaxation time (T2) and highly coordinated water molecules. The physical and electrostatic barrier emerged from the epitaxial ordering of water results in a particular ionic distribution, which can prevent the direct adsorption of a variety of chemical species. The implications of our results delineate important contributions to the current understanding of crystallization and biomineralization processes.