A molecular dynamics study of the effect of water diffusion into bio-active phosphate-based glass surfaces on their dissolution behaviour

Classical molecular dynamics (MD) simulations were used to study the effects of water on the structural relaxation of the surfaces of bio-active phosphate-based glasses with compositions (P2O5)(0.45)(CaO)(x)(Na2O)(0.55-x) (x = 0.30, 0.35 and 0.40). Direct comparison of the data for the three compositions showed that surfaces with x = 0.30 experienced the highest calcium diffusion, as well as highest sodium concentration at the glass/water interface, confirming these systems as the most soluble of the three compositions studied. Our results also show the importance of surface hydroxylation in the simulation of these types of bio-glasses, which causes differential relaxation of the surfaces, leading to changes in network polymerization that modulate the diffusion of water and modifiers into and out of the glasses, with direct impact on dissolution.