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Now showing items 1 - 16 of 20817

  • Topological understanding of the mixed alkaline earth effect in glass

    Ding, Zhijie   Wilkinson, Collin J.   Zheng, Jinfeng   Lin, Yinan   Liu, Hongshen   Shen, Jianxing   Kim, Seong H.   Yue, Yuanzheng   Ren, Jinjun   Mauro, John C.   Zheng, Qiuju  

    The mixed alkaline earth effect (MAEE) is important for several families of industrial borosilicate and aluminosilicate glasses, including glasses used in pharmaceutical packaging and as substrates for flat panel displays. Despite the technological importance of the mixed alkaline earth effect, the physical origin of this phenomenon is not well understood, and there is currently no model to offer quantitative prediction of the effect. In this work, the MAEE is studied both experimentally and through modeling in a series of boroaluminosilicate glasses with systematic substitution of CaO with MgO. The network structure is characterized by magic angle spinning nuclear magnetic resonance (MAS NMR) analyses of Al-27, B-11, Si-29, and Na-23. Molecular dynamics (MD) simulations are conducted to simulate the glass structures and calculate the evolution of the bond angle distributions with composition. Based on the structural data, a topological constraint model is proposed to capture the MAEE on glass transition temperature (T-g), liquid fragility index (m), and Young's modulus (E) of the glasses. Results of the topological constraint model are in good quantitative agreement with experimental data. The success of the constraint model confirms that the mixed alkaline earth effect is the result of a shift in angle around oxygen in the cation-oxygen-cation bond in the glass network. This is related to the constraint strength that ultimately governs the nonlinear property variation.
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  • Glass-activated regeneration of volumetric muscle loss

    Jia, Weitao   Hu, Haoran   Li, Aize   Deng, Huayun   Hogue, Carrie L.   Mauro, John C.   Zhang, Changqing   Fu, Qiang  

    Volumetric muscle loss (VML) resulting from injuries to skeletal muscles has profound consequences in healthcare. Current VML treatment based on the use of soft materials including biopolymers and decellularized extracellular matrix (dECM) is challenging due to their incapability of stimulating the formation of satellite cells (SCs), muscle stem cells, which are required for muscle regeneration. Additional stem cells and/or growth factors have to be incorporated in these constructs for improved efficacy. Here we report an approach by using bioactive glasses capable of regenerating VML without growth factors or stem cells. One silicate and two borate compositions with different degradation rates (2.4% for silicate 45S5; 5.3% and 30.4% for borate 8A3B and 13-9383, respectively, in simulated body fluid (SBF) at 37 degrees C for 30 days) were used for this study. Our in vitro models demonstrate the ability of ions released from bioactive glasses in promoting angiogenesis and stimulating cells to secrete critical muscle-related growth factors. We further show the activation of SCs and the regeneration of skeletal muscles in a rat VML model. Considering these promising results, this work reveals a potentially simple and safe approach to regenerating skeletal muscle defects. Statement of significance (1) This is the first report on an inorganic material used in skeletal muscle regeneration through in vitro and in vivo models. (2) Bioactive glass is found to activate the production of satellite cells (SCs), muscle stem cells, without the incorporation of extra stem cells or growth factors. (3) The work represents a simple, safe, low-cost yet efficient means for healing muscle defects. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Predicting Ionic Diffusion in Glass from Its Relaxation Behavior

    Wilkinson, Collin J.   Doss, Karan   Cassar, Daniel R.   Welch, Rebecca S.   Bragatto, Caio B.   Mauro, John C.  

    In low-viscosity liquids, diffusion is inversely related to viscosity via the Stokes-Einstein relation. However, the Stokes-Einstein relation breaks down near the glass transition as the supercooled liquid transitions into the non-ergodic glassy state. The nonequilibrium viscosity of glass is governed by the liquid-state viscous properties, namely, the glass transition temperature and the fragility. Here, a model is derived to predict the ionic diffusivity of a glass from its nonequilibrium viscosity, accounting for the compositional dependence of the glass. The free energy activation barrier for diffusion is related to the activation enthalpy for viscous flow using the Mauro-Allan-Potuzak model of nonequilibrium viscosity [Mauro, J. C.; Allan, D. C.; Potuzak, M. Nonequilibrium Viscosity of Glass. Phys. Rev. B 2009, 80, 094204]. These insights allow for accurate prediction of activation barriers for diffusion of alkali ions. The model is supported by experimental results and nudged-elastic band calculations applied to sodium silicate and borate glasses.
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  • Effect of water on topological constraints in silica glass

    Potter, Arron R.   Wilkinson, Collin J.   Kim, Seong H.   Mauro, John C.  

    A fundamental understanding of how water interacts with glass is valuable for many practical concerns due to the myriad effects of water on glass properties. Topological constraint theory, which has been shown in prior studies to be an excellent model for various thermomechanical properties, is expanded herein to account for strain on the glass network, in this application due to unbonded interstitial species. Literature T-g data have been collected for silicate glasses containing various alkali and water contents and an expanded constraint theory model has been successfully applied to describe the effects of water on the glass transition temperature. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • On the Prony series representation of stretched exponential relaxation

    Mauro, John C.   Mauro, Yihong Z.  

    Stretched exponential relaxation is a ubiquitous feature of homogeneous glasses. The stretched exponential decay function can be derived from the diffusion-trap model, which predicts certain critical values of the fractional stretching exponent, beta. In practical implementations of glass relaxation models, it is computationally convenient to represent the stretched exponential function as a Prony series of simple exponentials. Here, we perform a comprehensive mathematical analysis of the Prony series approximation of the stretched exponential relaxation, including optimized coefficients for certain critical values of beta. The fitting quality of the Prony series is analyzed as a function of the number of terms in the series. With a sufficient number of terms, the Prony series can accurately capture the time evolution of the stretched exponential function, including its "fat tail" at long times. However, it is unable to capture the divergence of the first-derivative of the stretched exponential function in the limit of zero time. We also present a frequency-domain analysis of the Prony series representation of the stretched exponential function and discuss its physical implications for the modeling of glass relaxation behavior. (C) 2018 Elsevier B.V. All rights reserved.
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  • Viscous flow of medieval cathedral glass

    Gulbiten, Ozgur   Mauro, John C.   Guo, Xiaoju   Boratav, Olus N.  

    A popular urban legend concerns the apparent flow of stained glass windows in medieval cathedrals, where the glass windows are commonly observed to be thicker at the bottom than they are at the top. Advances in glass transition theory and experimental characterization techniques now allow for us to address this urban legend directly. In this work, we investigate the dynamics of a typical medieval glass composition used in Westminster Abbey. Depending on the thermal history of the glass, the room temperature viscosity is on the order of 10(24) to 10(25) Pa.s, about 16 orders of magnitude lower than found in a previous study of soda lime silicate glass. This measurement is in quantitative agreement with a newly derived model for the composition dependence of the nonequilibrium viscosity of glass. Despite this significantly lower value of the room temperature viscosity, the viscosity of the glass is much too high to observe measurable viscous flow on a human time scale. Using analytical expressions to describe the glass flow over a wall, we calculate a maximum flow of similar to 1 nm over a billion years.
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  • Statistical mechanical model of bonding in mixed modifier glasses

    Goyal, Sushmit   Mauro, John C.  

    Oxide glasses often consist of multiple network formers that create the backbone of the glass network and modifiers that serve as either charge compensators or creators of non-bridging oxygens. The variety of bonding preferences results in very rich composition-property relationships. In this work, we present a statistical description of the glass structure governed by the relative enthalpic and entropic contributions to the bonding preferences in a glassy system. Using the proposed model, we derive an analytical expression to represent the bonding in mixed modifier glasses and explain the role of composition and fictive temperature on glass structure. The model provides the criteria for nonlinearity in bonding preference and reveals regions where high fluctuations in local structure are predicted.
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  • Modeling of delayed elasticity in glass

    Zheng, Zheming   Mauro, John C.   Allan, Douglas C.  

    We have developed a numerical model based on finite element analysis (FEA) with a viscoelastic material model coupling stress relaxation and structural relaxation, using the Mauro-Allan-Potuzak (MAP) non-equilibrium viscosity equation as the shift function. A modeling study of the delayed elasticity behavior in glass under different equilibrium viscosity and non-equilibrium viscosity conditions is conducted. The delayed elastic response is found to be well described by a stretched exponential function with three parameters: the maximum delayed elasticity response, the retardation time of delayed elasticity response, and the stretching exponent of delayed elasticity response. The delayed elasticity magnitude is seen to increase with lower values of the stretching exponent b(stress). At equilibrium viscosity, the retardation time shows a linear relationship with the stress relaxation time. However, when the temperature drops sharply in the non-equilibrium viscosity cases, the delayed elastic response may be frozen resulting in a lower magnitude for the delayed elasticity and the retardation time is not linear any more with the stress relaxation time. The delayed elasticity stretching exponent is seen to vary slightly at different relaxation times and normalized delayed elasticity response can roughly be collapsed into a single master curve. The impact of liquid fragility is also studied.
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  • Perspectives on the scientific career and impact of Prabhat K. Gupta

    Varshneya, Arun K.   Zanotto, Edgar D.   Mauro, John C.  

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  • The relativistic glass transition: A thought experiment

    Wilkinson, Collin J.   Doss, Karan   Palmer, Greg   Mauro, John C.  

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  • Understanding Glass through Differential Scanning Calorimetry

    Zheng, Qiuju   Zhang, Yanfei   Montazerian, Maziar   Gulbiten, Ozgur   Mauro, John C.   Zanotto, Edgar D.   Yue, Yuanzheng  

    Differential scanning calorimetry (DSC) is a powerful tool to address some of the most challenging issues in glass science and technology, such as the nonequilibrium nature of the glassy state and the detailed thermodynamics and kinetics of glass-forming systems during glass transition, relaxation, rejuvenation, polyamorphic transition, and crystallization. The utility of the DSC technique spans across all glass forming chemistries, including oxide, chalcogenide, metallic, and organic systems, as well as recently discovered metal organic framework glass-forming systems. Here we present a comprehensive review of the many applications of DSC in glass science with focus on glass transition, relaxation, polyamorphism, and crystallization phenomena. We also emphasize recent advances in DSC characterization technology, including flash DSC and temperature-modulated DSC. This review demonstrates how DSC studies have led to a multitude of relevant advances in the understanding of glass physics, chemistry, and even technology.
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  • Atomic picture of structural relaxation in silicate glasses

    Song, Weiying   Li, Xin   Wang, Bu   Krishnan, N. M. Anoop   Goyal, Sushmit   Smedskjaer, Morten M.   Mauro, John C.   Hoover, Christian G.   Bauchy, Mathieu  

    As nonequilibrium materials, glasses continually relax toward the supercooled liquid state. However, the atomic-scale origin and mechanism of glass relaxation remain unclear. Here, based on molecular dynamics simulations of sodium silicate glasses quenched with varying cooling rates, we show that structural relaxation occurs through the transformation of small silicate rings into larger ones. We demonstrate that this mechanism is driven by the fact that small rings (<6-membered) are topologically overconstrained and experience some internal stress. At the atomic level, such stress manifests itself by a competition between radial and angular constraints, wherein the weaker bond-bending constraints yield to the stronger bond-stretching ones. These results strongly echo von Neumann's N - 6 rule in grain growth theory and suggest that the stability of both atomic rings and two-dimensional crystal grains is fully topological in nature.
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  • Topological Origins of the Mixed Alkali Effect in Glass

    Wilkinson, Collin J.   Potter, Arron R.   Welch, Rebecca S.   Bragatto, Caio   Zheng, Qiuju   Bauchy, Mathieu   Affatigato, Mario   Feller, Steven A.   Mauro, John C.  

    The mixed alkali effect, the deviation from expected linear property changes when alkali ions are mixed in a glass, remains a point of contention in the glass community. While several earlier models have been proposed to explain mixed alkali effects on ionic motion, models based on or containing discussion of structural aspects of mixed-alkali glasses remain rare by comparison. However, the transition-range viscosity depression effect is many orders in magnitude for mixed-alkali glasses, and the original observation of the effect (then known as the Thermometer Effect) concerned the highly anomalous temperature dependence of stress and structural relaxation time constants. With this in mind, a new structural model based on topological constraint theory is proposed herein which elucidates the origin of the mixed alkali effect as a consequence of network strain due to differing cation radii. Discussion of literature models and data alongside new molecular dynamics simulations and experimental data are presented in support of the model, with good agreement.
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  • Topological constraint model for the elasticity of glass-forming systems

    Wilkinson, Collin J.   Zheng, Qiuju   Huang, Liping   Mauro, John C.  

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  • Workplace accidents and self-organized criticality

    Mauro, John C.   Diehl, Brett   Marcellin, Richard F.   Vaughn, Daniel J.  

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  • Crack initiation in an indented metallic glass with embedded nanoparticle

    Lee, Kuo-Hao   Yang, Yongjian   Mauro, John C.  

    Nanoindentation was performed on a metallic glass with an embedded glassy nanoparticle using molecular dynamics simulations to investigate the effect of the second phase on shear band formation and crack initiation. It was found that the addition of a nanoparticle having a lower elastic modulus compared to that of matrix centralizes the region of shear strain below the indenter, which facilitates crack initiation. In contrast, the addition of a nanoparticle with a higher elastic modulus has the effect of branching the shear band, which confines the shear bands within the hydrostatic zone and suppresses crack initiation. Published under license by AIP Publishing.
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