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Origins of the non-exponential reorientation dynamics of nanoconfined water
Fogarty, Aoife C. Duboué-Dijon, Elise Laage, Damien Thompson, Ward H.
Fogarty, Aoife C.
Duboué-Dijon, Elise
Laage, Damien
Thompson, Ward H.
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Abstract
The dynamics of water are dramatically modified upon confinement in nanoscale hydrophilic silica pores. In particular, the OH reorientation dynamics of the interfacial water are non-exponential and dramatically slowed relative to the bulk liquid. A detailed analysis of molecular dynamics simulations is carried out to elucidate the microscopic origins of this behavior. The results are analyzed in the context of the extended jump model for water that describes the reorientation as a combination of hydrogen-bond exchanges, or jumps, and rotation of intact hydrogen bonds, with the former representing the dominant contribution. Within this model, the roles of surface and dynamical heterogeneities are considered by spatially resolving the hydrogen-bond jump dynamics into individual sites on the silica pore surface. For each site the dynamics is nearly mono-exponential, indicating that dynamical heterogeneity is at most a minor influence, while the distribution of these individual site jump times is broad. The non-exponential dynamics can also not be attributed to enthalpic contributions to the barriers to hydrogen-bond exchanges. Two entropic effects related to the surface roughness are found to explain the retarded and diverse dynamics: those associated with the approach of a new hydrogen-bond acceptor and with the breaking of the initial hydrogen-bond.
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This is the published version. Copyright 2014 American Institute of Physics
Date
2014
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American Institute of Physics
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Keywords
Hydrogen bonding, Surface dynamics, Nanoporous materials, Silica, Interface dynamics
Citation
Fogarty, Aoife C., Elise Duboué-Dijon, Damien Laage, and Ward H. Thompson. "Origins of the Non-exponential Reorientation Dynamics of Nanoconfined Water." The Journal of Chemical Physics J. Chem. Phys. 141.18 (2014). http://dx.doi.org/10.1063/1.4896983