Structure and Dynamics of Mineral-Water Interfaces: Nanoscale View from the Computational Molecular Modeling Perspective

Molecular-level knowledge of the thermodynamic, structural, and transport properties of water at mineral interfaces is crucial for quantitative understanding and prediction of many geochemical and environmental processes. Experimental nanoscale studies of interfacial water structure and dynamics are not always feasible, and their results often require considerable interpretation. Computational molecular modeling significantly complements such experimental efforts and provides new important atomic-scale insights for the interpretation of the observed interfacial phenomena and the effects of mineral surface structure and composition on the structure and properties of interfacial aqueous solutions.

We use molecular dynamics (MD) computer simulations to study complex structural and dynamical behavior of water molecules and ions at the surfaces of metal oxides and hydroxides, mica, talc, clays, and hydrous cement phases. MD simulations also demonstrate great potential in significantly improving our interpretation of the spectra of complex, low frequency vibrational, rotational and translational modes associated with interlayer and surface species in hydrous layered minerals, thus providing molecular scale quantitative insight into the structure and dynamics of these important limiting cases of nano-confined fluids.

The structure and composition of mineral substrates significantly affect the structure of the interfacial aqueous layer, the effective diffusion rates of surface species, their lifetimes, translational and librational dynamics. Interfacial water molecules and ions simultaneously participate in several dynamic processes characterized by wide ranges of time- and length- scales. The first molecular layer of water at all surfaces is always highly ordered and has reduced translational and orientational mobility. This ordering is not simply “ice-like”, but resembles the behavior of supercooled water or amorphous ice, although with significant substrate-specific variations. At some surfaces, water molecules can easily form strong donating and accepting hydrogen bonds, thus developing stable interfacial H-bonding networks. However, at many surfaces the formation of such networks is hindered by the unfavorable surface charge distribution.