Surface Chemistry Affects the Efficacy of the Hydration Force between Two ZnO(101̅0) Surfaces

Abstract

The hydration force is an important component of the energy landscape for particle−particle aggregation. Here, we use molecular simulation to investigate the length scale and the oscillatory nature of the hydration force that manifests between two hydrophilic surfaces that undergo hydroxylation in water. We identify how this force is modified due to the details of chemistry at the interface of ZnO(101̅ 0) in aqueous solution. Importantly, our research demonstrates that the size-dependent nature of oriented attachment does not originate from the hydration force. Rather, we find that the hydration force has qualitatively different outcomes based on the details of the surface chemistry, occurring at structurally specific aqueous solid−liquid interfaces.

Connecting energetics to dynamics in particle growth by oriented attachment using real-time observations

“…However, classical molecular dynamics (MD) simulations in that study 12 , as well as that of Shen et al 47 for the case of ZnO(101̅ 0) surfaces predicted that hydration forces between two approaching zinc oxide particles produce significant repulsive barriers at subnanometer particle separation, which contrasts with the above experimental findings that the measured energy barrier is practically negligible. Moreover, the MD simulations do not predict significant interparticle interactions beyond 1 nm, while the experimental data demonstrate torques beyond 5 nm and attractive interactions out to 10 nm.…”

“…Moreover, the MD simulations do not predict significant interparticle interactions beyond 1 nm, while the experimental data demonstrate torques beyond 5 nm and attractive interactions out to 10 nm. The MD results also indicate that a possible reason for the discrepancy in the barriers is that the repulsive hydration force depends strongly on the surface chemistry 47 , as well as curvature in the case of small particles 48 . Importantly, molecular simulations under the low salt concentration solution conditions relevant to this study would require prohibitively large and long simulations to provide insight into the long range solution-mediated interactions and standard molecular potentials are not parametrized to capture long-range dispersion interactions between nanoparticles 32 .…”

“…Previous analyses of potentials between ZnO faces based on MD simulations predicted multiple barriers far in excess of kT within about 1 nm of the surface due to the formation of hydration layers near the crystal in aqueous solution 12,47 . The inclusion of electrostatic, ion correlation and van der Waals forces appears to resolve the disagreement between the MD predictions and the experimental observation that barriers are insignificant.…”

Natural, incidental, and engineered nanomaterials and their impacts on the Earth system

“…Direct measurements of interparticle forces in controlled environments with very high precision are now possible (113,114). Present-day molecular simulations can encompass aspects of directionspecific nanomaterial interactions in aqueous solutions, such as predicting potentials of mean force for direction-specific interactions (113,115). However, much remains unknown about the fundamental basis for oriented versus nonoriented aggregation and homo-versus heteroaggregation.…”

Lateral water structure connects metal oxide nanoparticle faces

“…It remains a challenge to incorporate nanoscale and molecular scale phenomena into computationally tractable analytical models of EDL properties. Recent contributions have described modified EDL models incorporating interface roughness [41,42,43,44,45,61] or finite ion correlations [42,62,63,64,65,66]. In principle, classical EDL models could incorporate both vertical and lateral water polarization phenomena if the Poisson's equation [Eq.…”