Orientational dynamics of water trapped between two nanoscopic hydrophobic solutes: A molecular dynamics simulation study.

We investigate thoroughly the effect of confinement and solute topology on the orientational dynamics of water molecule in the interplate region between two nanoscopic hydrophobic paraffinlike plates. Results are obtained from molecular dynamics simulations of aqueous solutions of paraffinlike plates in the isothermal-isobaric ensemble. An analysis of survival time auto correlation function shows that the residence time of the water molecule in the confined region between two model nanoscopic hydrophobic plates depends on solute surface topology (intermolecular distance within the paraffinlike plate). As expected, the extent of confinement also changes the residence time of water molecules considerably. Orientational dynamics was analyzed along three different directions, viz., dipole moment, HH, and perpendicular to molecular plane vectors. It has been demonstrated that the rotational dynamics of the confined water does not follow the Debye rotational diffusion model, and surface topology of the solute plate and the extent of confinement have considerable effect on the rotational dynamics of the confined water molecules.