Neutron scattering and ab initio molecular dynamics study of cross-linking in biomedical phosphate glasses

• Published in: Journal of physics. Condensed matter 2010-12, Vol.22 (48), p.485403-485403
• Main Authors: Parsons, A J, Ahmed, I, Rudd, C D, Cuello, G J, Pellegrini, E, Richard, D, Johnson, M R
• Format: Article
• Language: English
• Subjects: Biocompatible Materials - chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Cross-Linking Reagents; Disordered solids; Electron states; Exact sciences and technology; Glass - chemistry; Glasses; Glasses (including metallic glasses); Materials science; Methods of electronic structure calculations; Molecular Dynamics Simulation; Neutron Diffraction; Neutron diffraction and scattering; Neutron scattering techniques (including small-angle scattering); Phosphates - chemistry; Physics; Specific materials; Structure of solids and liquids; crystallography
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/22/48/485403

Details of the microscopic structure of phosphate glasses destined for biomedical applications, which include sodium, magnesium and calcium cations, have been obtained from the static structure factor measured by means of neutron scattering. A complementary, molecular dynamics study has been performed on a range of phosphate glasses using density functional theory methods, which allow structural fluctuations, including bond breaking, in the liquid phase before quenching to the glass phase. Good agreement between experiment and simulation allows the molecular dynamics trajectories to be analysed in detail. In particular, attention is focused on the cross-linking of divalent cations in contrast with the structural aspects associated with monovalent cations. Magnesium cations are found equidistant and bridging between the phosphorus atoms of different phosphate chains, leading to a shorter phosphorus-phosphorus second neighbour distance (that is, a more compact packing of neighbouring phosphate chains) compared to the effect of sodium cations. Calcium cations show behaviour intermediate between those of magnesium and sodium. Molecular dynamics simulations give access to the cation mobility, which is lowest for magnesium, reflecting its structural, cross-linking role.