On the computer simulation of silicate glass surfaces

The surface layer of xNa(2)O(1-x)SiO2 (x=0.245) was simulated by the molecular dynamics. The glass transition temperatures T-g (for the molecular dynamics time scale) in the bulk and for the surface layer were determined by the method of inherent structures. In the bulk T-g is larger than at the surface. The isotherm of adsorption of CO2 was also simulated on that model surface by grand canonical Monte Carlo. The isotherm for the unannealed surface lies higher than that on the annealed one but the difference between them is considerably smaller than that for the corresponding surfaces of silica. The correlation between the stability (chemical durability) of the surface and physical adsorption is discussed. It is shown that molecules of CO2 can penetrate more than 2 nm under the surface of the silicate. (C) 2001 American Institute of Physics.