Effect of adsorption on the surface structure of sodium alumino-silicate glasses: a molecular dynamics simulation

Abstract

Classical molecular dynamics (MD) computer simulations were used to study adsorption of model metals onto sodium alumino-silicate glasses and the effect these adsorbates have on the surface structure of the glass substrates. Multibody potentials were used to describe the substrate-substrate interactions; Lennard-Jones potentials were used to describe the adsorbate-adsorbate and adsorbate-substrate interactions. Lennard-Jones parameters and adsorbate mass were chosen to model Pt as the adsorbate. The adsorbate atoms penetrated 5–6Å into the glass, with multilayer coverage eventually occurring during deposition. The substrate showed a slight compression of the surface due to the presence of the adsorbate film. There was also a pronounced shift to smaller bond angles in the distribution of siloxane bond angles at the bridging oxygen. This redistribution was predominantly caused by a compression of siloxane bonds in 5 and 6 membered rings, although there was a partial rearrangement of ring sizes. Finally, Na at the surface were displaced by the adsorbate atoms such that Na were observed in the adsorbate film and at the film/vacuum interface.