Classical molecular dynamics (MD) simulations are performed to study structural
and dynamic properties of water confined within graphite surfaces. The surfaces are
separated at distances varying between 7 and 14.5 Å and the water density is held
constant at 1g/cc. Results at 298 K show the formation of a well-ordered structure
constituted by water layers parallel to the graphite surfaces. The water molecules in the
layers in contact with the surface have a tendency to orient their dipole parallel to the
surface. Such ice-like structures may have different structural and dynamic properties
than those of ice. The calculated mean square displacement reveals that the mobilities of
the confined water at a separation of 8 Å become similar to that of low-temperature
water (213 K) at the same density, although the structures of water are very different.
The temperature at which the mobility of water confined at the separation of 7 Å would
become similar to that of bulk low-temperature water was found to be 373K. With
respect to the dynamics of confined water, a significant blue shift is observed in the
intermolecular vibrational modes associated with the O×××O×××O bending and O×××O
stretching of molecules linked by hydrogen bonds.
The analysis of the geometry of water clusters confined between two graphite
surfaces has been performed using ab initio methods. The ab initio calculations yield two
preferential orientations of water molecules which are; 1) one O-H bond points to the
surface and the other is parallel; 2) both O-H bonds are parallel to the surface. These
orientations agree with those found in our MD simulation results. The calculated energy
barriers for proton transfer of the confined H3O+-(H2O) complexes between two graphite model surfaces suggest that the confinement enhances the proton transfer at the
separation 6-14.5 Å. When the confinement is high, at a separation of 4 Å, the barrier
energies are extremely large. The confinement does not enhance proton transfer when
the H3O+-(H2O) complexes are located further from the surfaces by more than 8 Å. As a
result, the barrier energies start to increase at the separation of 20 Å.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1264 |
| Date | 15 May 2009 |
| Creators | Hirunsit, Pussana |
| Contributors | Balbuena, Perla B. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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