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Surface Structure and Stability of Partially Hydroxylated Silica Surfaces
journal contribution
posted on 2017-04-04, 15:49 authored by J. M. Rimsza, R. E. Jones, L. J. CriscentiSurface
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/m2 is
calculated with the ClayFF force field, and 2.0 J/m2 is
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/m2 for ClayFF
and 0.8 J/m2 for ReaxFF. Posthydroxylation surface energies
decreased further to 4.6 J/m2 with the ClayFF force field
and to 0.2 J/m2 with 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.
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ReaxFF force fieldsilicates influence crack propagationMDforce fieldforce field reactivityClayFF force fieldPartially Hydroxylated Silica Surfaces Surface energiesPosthydroxylation surface energiesunhydroxylated fracture surface energyClayFF surface energiessurface energy valueslow-energy equilibrium surfaceequilibrium surface energiessurface energiesExperimental equilibrium surface energies
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