Effects of confinement on water structure and dynamics: A molecular simulation study
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abstract
Classical molecular dynamics simulations are performed to study structural and dynamic properties of water confined within graphite surfaces separated by a distance varying between 7 and 14.5 , at a constant water density of 1 g/cm 3. 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 layers in contact with the surface have a tendency to orient their dipole parallel to the surface. Such ice-like structure may have, however, different structural and dynamical properties than those of ice. The time evolution of the calculated mean square displacement reveals that at the smallest separation (7 ) the water mobility is significantly lower than that of low-temperature water (213 K) at the same density; the mobilities become similar at a separation of 8 although the structure of that confined water is very different from that in low-temperature water. The temperature at which the mobility of water confined between graphite walls separated at 7 would become similar to that in bulk low-temperature water was found to be 373 K. With respect to the dynamics of confined water, a significant blue shift is observed in the intermolecular vibrational modes associated with the O OO bending and OO stretching of molecules linked by hydrogen bonds. 2007 American Chemical Society.
