Nanotribology of water confined between hydrophilic alkylsilane self-assembled monolayers

We report the results of large-scale molecular dynamics simulations of water confined between alkylsilane Si(OH)(3)(CH2)(10)COOH self-assembled monolayers (SAMs) on an amorphous silica substrate. The structure and dynamics of the confined water are studied for applied pressures ranging from approximately 50 to 400 MPa. The viscosity and microscopic friction of the confined water are determined from steady-state shear simulations. We find that the viscosity of the water increases only slightly compared with bulk water under comparable pressures. There is no evidence of ice-like layers being formed near the COOH end groups of the SAMs. The microscopic friction coefficients could only be calculated at high shear rates due to the low viscosity of the water and are found to decrease with increasing amounts of water, similar to experiment