Cooperative effects at water-crystalline silica interfaces strengthen surface silanol hydrogen bonding. An ab initio molecular dynamics study

Silica and silica based materials are widely used in chemistry and materials science due to their importance in many technological fields. The properties of these materials, which are crucial for their applications, are mainly determined by the presence of hydrogen bonding between surface silanols. Here, we present ab initio molecular dynamics simulations (AIMD) on different surfaces derived from the crystallographic α-quartz (100) and the α-cristobalite (001) and (101) faces, both free and at the interface with liquid water. The focus was on studying whether water adsorption can disrupt the H-bond pattern at the pristine free silica surface and how deep the perturbation due to the contact with the surface affects the structure of the water multilayer. Results highlight that the water phase is over structured at the interface with silica, as compared to water bulk. Furthermore, an apparent counterintuitive behavior has been observed for quartz (100) and cristobalite (001) surfaces: the interaction with water does not cleave the pre-existent H-bonds between the surface silanol groups. On the contrary, in several cases, it is observed that SiOHOHSi H-bonds are even strengthened, as the result of a mutual cooperative H-donor/H-acceptor enhancement between silanols and water molecules, which may alter the adsorption capability of these silica surfaces.