| Abstract
| - The potential of molecular dynamics (MD) simulation for the study and prediction of particle/particleand particle/wall interaction in the wide context of technology has been explored. The present study concernsthe nature of adsorbed water and its effect on the interaction between two surfaces. Computer models oftwo opposing (1,0,−1) crystal surfaces of α-quartz (dimensions 5.49 × 4.91 nm) were constructed and upto 1500 water molecules positioned between the surfaces. The simulations were performed in the NVTensemble in “math mode” at a temperature of 300 K. The axial profiles of density and mobility (the latterresolved in planar and axial components) in the adsorbed layers were studied. The separation betweenthe crystal surfaces was varied, monitoring the adsorbed layer morphology and the forces acting on thecrystals. Most of the simulations shown are with 1500 molecules between the plates, giving around 3.1adsorbed monolayers, corresponding to a relative saturation (humidity) of 67% according to the BETisotherm. The density profiles show an ordered packing of molecules in the first two adsorbed layers withdensity peaks considerably higher than in bulk water and a low molecular mobility. The density tails offto zero, and the mobility rises to above that of bulk water at the surface of the adsorbed layer, which wasclearly defined but undulating. Determination of the forces acting on the crystals was difficult due to strongfluctuations on a short time scale, so only simulations for long times yielded statistically significant averageforces. At a surface separation of 3 nm, spontaneous bridge forming took place, paired with significantattractive forces between the crystals. The nature of the bridge is discussed. The observed bridging andresulting surface/surface force are shown to be roughly consistent with expectations based on macroscopictheory represented by the BET isotherm, the Kelvin equation (using the surface tension of bulk water),and a bridging force calculated from pressure-deficiency and surface tension contributions.
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