title: Surface Structure and Stability of Partially Hydroxylated Silica Surfaces.
abstract: Surface energies of silicates influence crack propagation during brittle fracture and decrease with surface relaxation caused by annealing and hydroxylation. Molecular-level simulations are particularly suited for the investigation of surface processes. In this work, classical MD simulations of silica surfaces are performed with two force fields (ClayFF and ReaxFF) to investigate the effect of force field reactivity on surface structure and energy as a function of surface hydroxylation. An unhydroxylated fracture surface energy of 5.1 J/m2is calculated with the ClayFF force field, and 2.0 J/m2is calculated for the ReaxFF force field. The ClayFF surface energies are consistent with the experimental results from double cantilever beam fracture tests (4.5 J/m2), whereas ReaxFF underestimated these surface energies. Surface relaxation via annealing and hydroxylation was performed by creating a low-energy equilibrium surface. Annealing condensed neighboring siloxane bonds increased the surface connectivity, and decreased the surface energies by 0.2 J/m2for ClayFF and 0.8 J/m2for ReaxFF. Posthydroxylation surface energies decreased further to 4.6 J/m2with the ClayFF force field and to 0.2 J/m2with the ReaxFF force field. Experimental equilibrium surface energies are ∼0.35 J/m2, consistent with the ReaxFF force field. Although neither force field was capable of replicating both the fracture and equilibrium surface energies reported from experiment, each was consistent with one of these conditions. Therefore, future computational investigations that rely on accurate surface energy values should consider the surface state of the system and select the appropriate force field.
authors.affiliation: Geochemistry Department, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
authors.forename: J M
authors.identifier: 0000-0003-0492-852X
authors.initials: JM
authors.lastname: Rimsza
authors.affiliation: Science-Based Material Modeling Department, Sandia National Laboratories , Livermore, California 94551, United States.
authors.forename: R E
authors.initials: RE
authors.lastname: Jones
authors.affiliation: Geochemistry Department, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
authors.forename: L J
authors.identifier: 0000-0002-5212-7201
authors.initials: LJ
authors.lastname: Criscenti