Computer simulation of water molecules at kaolinite and silica surfaces

Molecular dynamics simulations of water molecules at the surface of kaolini te, and of amorphous silica, have been carried out. In contrast to previous work, clay and silica atoms are not kept fixed at their crystallographic p ositions; all atoms are allowed to move. In both cases water molecules at t he surface show a marked decrease in the self-diffusion coefficient and an increase in the rotational correlation time. We consider the effects of inc reasing the ionic strength of the water. Comparison with experimental data is made by linking calculated diffusion and rotational correlation times to available pulse field gradient nuclear magnetic resonance spectroscopy and relaxation measurements.