Viscosity of Nanoconfined Water between Hydroxyl Basal Surfaces of Kaolinite: Classical Simulation Results

Whereas the structure of water near kaolinite surfaces is now fairly well understood, the dynamics of water confined between two kaolinite surfaces has not been studied. We conducted classical molecular dynamics simulations of nanoconfined water under shear between the hydroxyl basal planes of two kaolinite substrates to study the structural and dynamic properties of the nanoconfined water as a function of the amount of water in the system and the applied load. We found that the orientation of the water molecules within the first monolayer (similar to 3 angstrom) of the kaolinite interfaces changes as a function of load on the system. At low loads, the majority of the water molecules are oriented with one OH bond parallel to the kaolinite interface and the hydrogen atom of the other OH bond nearer to the kaolinite interface and a smaller population of water molecules are oriented with both hydrogen atoms further from the interface than the oxygen atom. At higher loads, while the same orientations are observed, another population of water molecules are oriented with one OH bond parallel to the interface and one OH bond in which the oxygen atom is nearest to the kaolinite interface is observed. The maximum value of viscosity observed is only 1 order of magnitude larger than the bulk shear viscosity at the same pressure.