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Tao J.-Y.,Beijing Normal University | Mu W.-H.,Yunnan Normal University | Chass G.A.,Queen Mary, University of London | Chass G.A.,NRC Steacie Institute for Molecular Sciences | And 7 more authors.
International Journal of Quantum Chemistry | Year: 2013

Toward cracking the problem of understanding, characterizing, and predicting "solvent-effect" while the world awaits an effective explicit solvent model, we introduce and justify herein a novel set of atomic radii to be used within the most commonly used continuum reaction field, the polarizable continuum model (PCM). The radial values emerge from a quantitative description of the elemental electronic density distribution and are shown to be accurate in such a self-consistent reaction field (SCRF); labeled accordingly as isodensity-based SCRF (IDSCRF) radii. Transition row elements with dynamic oxidation states are addressed through an averaging of the electronic properties from all states in the determination of their effective radii. All results for nonmetal elements have been verified with Guthrie's SAMPLE1 test set and are in quantitative agreement with experimental values from the literature and self-consistent isodensity polarizable continuum model (SCIPCM) calculations. For the compounds with transition metal elements, our IDSCRF results have been verified with SCIPCM results as there are rarely experimental results available. Finally, explicit solvent particles "solvating" Pd- and Ni-containing homogeneous catalysts are also shown to be in close agreement with the IDSCRF radii calculations. © 2012 Wiley Periodicals, Inc.

Tian K.V.,Semmelweis University | Tian K.V.,NRC Steacie Institute for Molecular Sciences | Tian K.V.,Global Institute of Computational Molecular and Materials Science GIOCOMMS | Nagy P.M.,Semmelweis University | And 10 more authors.
Journal of Materials Science: Materials in Medicine | Year: 2012

Discs of biocompatible glass ionomer cements were prepared for Hertzian indentation and subsequent fracture analyses. Specifically, 2 × 10 mm samples for reproducing bottom-initiated radial fracture, complemented by 0.2 × 1 mm samples for optimal resolution with X-ray micro tomography (lCT), maintaining dimensional ratio. The latter allowed for accurate determination of volumetric- porosity of the fully cured material, fracture-branching through three Cartesian axes and incomplete bottom-initiated cracking. Nanocomputed tomography analyses supported the reliability of the lCT results. Complementary 2-dimensional fractographic investigation was carried out by optical and scanning electron microscopies on the larger samples, identifying fracture characteristics. The combined 3-D qualitative assessment of microstructure and fractures, complemented by 2-D methods, provided an increased understanding of the mechanism of mechanical failure in these cements. Specifically, cracks grew to link pores while propagating along glass-matrix interfaces. The methodological development herein is exploitable on related biomaterials and represents a new tool for the rational characterisation, optimisation and design of novel materials for clinical service. © 2012 Springer Science+Business Media, LLC.

Tian K.V.,Semmelweis University | Tian K.V.,Global Institute of Computational Molecular and Materials Science GIOCOMMS | Tian K.V.,NRC Steacie Institute for Molecular Sciences | Chass G.A.,Global Institute of Computational Molecular and Materials Science GIOCOMMS | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2016

Bioactive glass ionomer cements (GICs), the reaction product of a fluoro-alumino-silicate glass and polyacrylic acid, have been in effective use in dentistry for over 40 years and more recently in orthopaedics and medical implantation. Their desirable properties have affirmed GIC's place in the medical materials community, yet are limited to non-load bearing applications due to the brittle nature of the hardened composite cement, thought to arise from the glass component and the interfaces it forms. Towards helping resolve the fundamental bases of the mechanical shortcomings of GICs, we report the 1st ever computational models of a GIC-relevant component. Ab initio molecular dynamics simulations were employed to generate and characterise three fluoro-alumino-silicate glasses of differing compositions with focus on resolving the atomic scale structural and dynamic contributions of aluminium, phosphorous and fluorine. Analyses of the glasses revealed rising F-content leading to the expansion of the glass network, compression of Al-F bonding, angular constraint at Al-pivots, localisation of alumino-phosphates and increased fluorine diffusion. Together, these changes to the structure, speciation and dynamics with raised fluorine content impart an overall rigidifying effect on the glass network, and suggest a predisposition to atomic-level inflexibility, which could manifest in the ionomer cements they form. © the Owner Societies 2016.

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