Publications by authors named "John C Mauro"

74 Publications

Theory of structural relaxation in glass from the thermodynamics of irreversible processes.

Phys Rev E 2021 Jun;103(6-1):062606

Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

This work proposes a fundamental thermodynamic description of structural relaxation in glasses by establishing a link between the Prony series solution to volume relaxation derived from the principles of irreversible thermodynamics and asymmetric Lévy stable distribution of relaxation rates. Additionally, it is shown that the bulk viscosity of glass, and not the shear viscosity, is the transport coefficient governing structural relaxation. We also report the distribution of relaxation times and energy barrier heights underpinning stretched exponential relaxation. It is proposed that this framework may be used for qualitative and quantitative descriptions of the relaxation kinetics in glass.
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http://dx.doi.org/10.1103/PhysRevE.103.062606DOI Listing
June 2021

Atomistic Mechanisms of Thermal Transformation in a Zr-Metal Organic Framework, MIL-140C.

J Phys Chem Lett 2021 Jan 15;12(1):177-184. Epub 2020 Dec 15.

Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.

To understand the mechanisms responsible for thermal decomposition of a Zr-MOF (MIL-140C), we perform atomistic-scale molecular dynamics (MD) simulations and discuss the simulation data in comparison with the TEM images obtained for the decomposed Zr-MOF. First, we introduce the ReaxFF parameters suitable for the Zr/C/H/O chemistry and then apply them to investigate the thermal stability and morphological changes in the MIL-140C during heating. Based on the performed simulations we propose an atomic mechanism for the collapse of the MIL-140C and the molecular pathways for carbon monoxide formation, the main product of the MIL-140C thermal degradation. We also determine that the oxidation state of the ZrO clusters, evolved due to the thermal degradation, approximates the tetragonal phase of ZrO. Both simulations and experiments show a distribution of very small ZrO clusters embedded in the disrupted organic sheet that could contribute to the unusual high catalytic activity of the decomposed MIL-140C.
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http://dx.doi.org/10.1021/acs.jpclett.0c02930DOI Listing
January 2021

Mixed Alkali Effect in Silicate Glass Structure: Viewpoint of Si Nuclear Magnetic Resonance and Statistical Mechanics.

J Phys Chem B 2020 Nov 3;124(45):10292-10299. Epub 2020 Nov 3.

Department of Chemistry and Bioscience, Aalborg University, 9220 Aalborg, Denmark.

The mixed alkali effect in glasses is the deviation from linear property changes when alkali cations are mixed. The extent of this effect and its structural origin remain topics of interest. In this work, we use a statistical mechanics approach to predict the composition-structure relationship in mixed modifier NaO-KO-SiO glasses. This is achieved by accounting for the enthalpy between each pairwise alkali ion and silicate unit interaction. The initial enthalpy parameters are obtained based on experimental structural data for binary NaO-SiO and KO-SiO glasses, which can be transferred to predict the short-range order structure of mixed modifier glasses without additional free parameters. To this end, we have performed Si magic angle spinning NMR spectroscopy measurements on (NaO-(1 - )KO)-(100 - )SiO glasses with = 0, 0.25, 0.5, 0.75, and 1 and = 34, 42, and 50. Good agreement between experimental data and model predictions are observed. Finally, we use this information to discuss the relative entropic and enthalpic contributions to the mixed modifier effect in silicate glass structure.
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http://dx.doi.org/10.1021/acs.jpcb.0c07980DOI Listing
November 2020

Bauchy et al. Reply.

Phys Rev Lett 2020 05;124(19):199602

Department of Chemistry and Bioscience, Aalborg University, 9220 Aalborg, Denmark.

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http://dx.doi.org/10.1103/PhysRevLett.124.199602DOI Listing
May 2020

Why does BO suppress nepheline (NaAlSiO) crystallization in sodium aluminosilicate glasses?

Phys Chem Chem Phys 2020 Apr;22(16):8679-8698

Department of Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8065, USA.

The uncontrolled growth of nepheline (NaAlSiO4) crystals during the manufacturing of sodium aluminosilicate glasses via the fusion draw or float techniques and during the vitrification of some of the sodium- and alumina-rich nuclear waste glasses is a well-known problem. The addition of B2O3 to suppress the crystallization in these glasses is well documented in the literature. Another advantage of B2O3 is that it lowers the viscosity of the glass melt and, if incorporated in its trigonal coordination state, will improve the intrinsic damage resistance of the final glass product. Hence, B2O3 has been an integral component of glass compositions for advanced industrial applications and for nuclear waste vitrification. However, one major disadvantage of adding B2O3 to alkali aluminosilicate based glasses is its adverse impact on their chemical durability due to the rapid hydrolysis of B[3,4]-O-B[3,4] bonds in comparison to (Si, Al)-O-(Si, Al) bonds. Therefore, designing a boron-containing alkali aluminosilicate based functional glass with minimal tendency towards crystallization and high chemical durability requires an in-depth fundamental understanding of the mechanism through which B2O3 tends to suppress crystallization in these glasses. There is no current consensus on the fundamental mechanism through which B2O3 tends to suppress nepheline crystallization in these glasses. Based on the mechanisms described and the questions raised in the preceding literature, the present study focuses on addressing the ongoing debate through a detailed structural and thermo-kinetic investigation of glasses designed in the Na2O-Al2O3-B2O3-SiO2 based quaternary system over a broad composition space. Using a combination of Raman and (1D and 2D) nuclear magnetic resonance spectroscopies along with equilibrium and non-equilibrium viscosity, and liquidus temperature measurements, it has been shown that the substitution of Si-O-Al by Si-O-B linkages in the glass structure results in a significant increase in the glass forming ability as well as an increase in the liquidus viscosity (slower diffusivity), thereby suppressing the nepheline crystallization.
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http://dx.doi.org/10.1039/d0cp00172dDOI Listing
April 2020

Predicting Ionic Diffusion in Glass from Its Relaxation Behavior.

J Phys Chem B 2020 Feb 30;124(6):1099-1103. Epub 2020 Jan 30.

Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.

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. , , 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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http://dx.doi.org/10.1021/acs.jpcb.9b10645DOI Listing
February 2020

Relating structural disorder and melting in complex mixed ligand zeolitic imidazolate framework glasses.

Dalton Trans 2020 Jan;49(3):850-857

Department of Materials Science and Metallurgy, University of Cambridge, UK.

We report the formation of zeolitic imidazolate framework glasses incorporating three organic linkers, from their corresponding novel crystalline structures [Zn(Im2-x-ybImxmbImy)]. Structure-property relationships between chemical compositions and thermal properties are analysed, in addition to the effect on the nanoscale porosity of the glasses formed. A probabilistic model is used to explain melting and the glass transition temperatures of the obtained glasses and link to the nanoscale structural disorder of their crystalline starting structures.
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http://dx.doi.org/10.1039/c9dt03559aDOI Listing
January 2020

Glass-activated regeneration of volumetric muscle loss.

Acta Biomater 2020 02 9;103:306-317. Epub 2019 Dec 9.

Science and Technology Division, Corning Incorporated, Corning, NY 14831, USA. Electronic address:

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 13-93B3, respectively, in simulated body fluid (SBF) at 37 °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.
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http://dx.doi.org/10.1016/j.actbio.2019.12.007DOI Listing
February 2020

Mechanical properties of bioactive glasses, ceramics, glass-ceramics and composites: State-of-the-art review and future challenges.

Mater Sci Eng C Mater Biol Appl 2019 Nov 16;104:109895. Epub 2019 Jun 16.

School of Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.

The repair and restoration of bone defects in orthopaedic and dental surgery remains a major challenge despite advances in surgical procedures and post-operative treatments. Bioactive glasses, ceramics, glass-ceramics and composites show considerable potential for such applications as they can promote bone tissue regeneration. This paper presents an overview of the mechanical properties of various bioactive materials, which have the potential for bone regeneration. It also identifies current strategies for improving the mechanical properties of these novel materials, as these are rarely ideal as direct replacements for human bone. For this reason bioactive organic-inorganic composites and hybrids that have tailorable mechanical properties are of particular interest. The inorganic component (bioactive glass, ceramic or glass-ceramic) can provide both strength and bioactivity, while the organic component can add structural reinforcement, toughness and processability. Another topic presented in this paper includes 3D porous scaffolds that act as a template for cell attachment, proliferation and bone growth. Mechanical limitations of existing glass and ceramic scaffolds are discussed, along with the relevant challenges and strategies for further improvement. Advantages and disadvantages of different bioactive materials are critically examined. This paper is focused on optimization of biomaterials properties, in particular mechanical properties and bioactivity.
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http://dx.doi.org/10.1016/j.msec.2019.109895DOI Listing
November 2019

Statistical Mechanical Model of Topological Fluctuations and the Intermediate Phase in Binary Phosphate Glasses.

J Phys Chem B 2019 Sep 22;123(35):7640-7648. Epub 2019 Aug 22.

Department of Chemistry and Bioscience, Aalborg University, 9220 Aalborg, Denmark.

Glasses are topologically disordered materials with varying degrees of fluctuations in structure and topology. This study links statistical mechanics and topological constraint theory to quantify the degree of topological fluctuations in binary phosphate glasses. Because fluctuations are a potential mechanism enabling self-organization, we investigated the ability of phosphate glasses to adapt their topology to mitigate localized stresses, e.g., in the formation of a stress-free intermediate phase. Results revealed the dependency of both glass composition and temperature in governing the ability of a glass network to relax localized stresses and achieve an ideal, isostatic state; also, the possibility of a second intermediate phase at higher modifier content was found.
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http://dx.doi.org/10.1021/acs.jpcb.9b05932DOI Listing
September 2019

Topological Origins of the Mixed Alkali Effect in Glass.

J Phys Chem B 2019 Aug 15;123(34):7482-7489. Epub 2019 Aug 15.

Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.

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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http://dx.doi.org/10.1021/acs.jpcb.9b06512DOI Listing
August 2019

Topological Control of Water Reactivity on Glass Surfaces: Evidence of a Chemically Stable Intermediate Phase.

J Phys Chem Lett 2019 Jul 2;10(14):3955-3960. Epub 2019 Jul 2.

Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.

Glass surfaces are of considerable interest due to their disproportionately large influence on the performance of glass articles in many applications. However, the behavior of glass surfaces has proven difficult to model and predict due to their complex structure and interactions with the environment. Here, the effects of glass network topology on the surface reactivity of glasses have been investigated using reactive and nonreactive force field-based molecular dynamics simulations as well as density functional theory. A topological constraint-based description for surface reactivity is developed, allowing for improved understanding of the physical and chemical origins of surface reactivity. Results show evidence for the existence of a chemically stable intermediate phase on the surface of the glass where the glass network is mechanically isostatic.
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http://dx.doi.org/10.1021/acs.jpclett.9b01275DOI Listing
July 2019

Understanding Glass through Differential Scanning Calorimetry.

Chem Rev 2019 Jul 23;119(13):7848-7939. Epub 2019 May 23.

School of Materials Science and Engineering , Qilu University of Technology (Shandong Academy of Sciences) , Jinan 250353 , China.

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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http://dx.doi.org/10.1021/acs.chemrev.8b00510DOI Listing
July 2019

Optical properties of a melt-quenched metal-organic framework glass.

Opt Lett 2019 Apr;44(7):1623-1625

Metal-organic framework (MOF) glasses are characterized by the possession of both inorganic and organic components, linked in a continuous network structure by coordination bonds. To the best of our knowledge, the optical properties of MOF glasses have not been reported until now. In this work, we prepared a transparent bubble-free bulk MOF glass, namely, the ZIF-62 glass (ZnImbIm), using our newly developed hot-pressing technique, and measured its optical properties. The ZIF-62 glass has a high transmittance (up to 90%) in the visible and near-infrared wavelength ranges, which is comparable to that of many oxide glasses. Using the Becke line n method, we found that the ZIF-62 glass exhibits a refractive index (1.56) similar to most inorganic glasses, though a lower Abbe number (∼31).
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http://dx.doi.org/10.1364/OL.44.001623DOI Listing
April 2019

Modifier clustering and avoidance principle in borosilicate glasses: A molecular dynamics study.

J Chem Phys 2019 Jan;150(4):044502

Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095, USA.

Oxide glasses are typically described as having a random, disordered skeleton of network-forming polyhedra that are depolymerized by network-modifying cations. However, the existence of local heterogeneity or clustering within the network-forming and network-modifying species remains unclear. Here, based on molecular dynamics simulations, we investigate the atomic structure of a series of borosilicate glasses. We show that the network-modifying cations exhibit some level of clustering that depends on composition-in agreement with Greaves' modified random network model. In addition, we demonstrate the existence of some mutual avoidance among network-forming atoms, which echoes the Loewenstein avoidance principle typically observed in aluminosilicate phases. Importantly, we demonstrate that the degree of heterogeneity in the spatial distribution of the network modifiers is controlled by the level of ordering in the interconnectivity of the network formers. Specifically, the mutual avoidance of network formers is found to decrease the propensity for modifier clustering.
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http://dx.doi.org/10.1063/1.5051746DOI Listing
January 2019

Statistical Mechanical Modeling of Borate Glass Structure and Topology: Prediction of Superstructural Units and Glass Transition Temperature.

J Phys Chem B 2019 Feb 24;123(5):1206-1213. Epub 2019 Jan 24.

Department of Chemistry and Bioscience , Aalborg University , 9220 Aalborg , Denmark.

Predicting the compositional evolution of the atomic-scale structure and properties of oxide glasses is important for designing new materials for advanced applications. A statistical mechanics-based approach has recently been applied to predict the composition-structure evolution in binary phosphate glasses, while topological constraint theory (TCT) has been applied in the last decade to predict the structure-property evolution in various oxide and nonoxide glass systems. In this work, we couple these two approaches to enable quantitative predictions of the compositional dependence of glass transition temperature and the population of superstructural units. The object of the study is the lithium borate glass system because they feature interesting structural characteristics (e.g., boron anomaly), and ample structure and property data are available. In these glasses, the average coordination number of boron first increases when lithium modifiers are added and then later decreases accompanied by network depolymerization. First, on the basis of B nuclear magnetic resonance spectroscopy data from literature, we present a statistical description of the structural evolution in lithium borate glasses by accounting for the relative enthalpic and entropic contributions to the bonding preferences. We show that the entire glass structure evolution (both short- and intermediate-range) can be predicted based on experimental structural information for only a few glass compositions. We then show that the developed structural model can be combined with a previously established TCT model to predict the compositional evolution of the glass transition temperature. This work thus opens a new avenue for the computational design of glasses with tailored properties.
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http://dx.doi.org/10.1021/acs.jpcb.8b11926DOI Listing
February 2019

Prediction of the Glass Transition Temperatures of Zeolitic Imidazolate Glasses through Topological Constraint Theory.

J Phys Chem Lett 2018 Dec 3;9(24):6985-6990. Epub 2018 Dec 3.

Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.

A topological constraint model is developed to predict the compositional scaling of glass transition temperature ( T) in a metal-organic framework glass, aZIF-62 [Zn(ImbIm )]. A hierarchy of bond constraints is established using a combination of experimental results and molecular dynamic simulations with ReaxFF. The model can explain the topological origin of T as a function of the benzimidazolate concentration with an error of 3.5 K. The model is further extended to account for the effect of 5-methylbenzimidazolate, enabling calculation of a ternary diagram of T with a mixture of three organic ligands in an as-yet unsynthesized, hypothetical framework. We show that topological constraint theory is an effective tool for understanding the properties of metal-organic framework glasses.
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http://dx.doi.org/10.1021/acs.jpclett.8b03348DOI Listing
December 2018

Unusual thermal response of tellurium near-infrared luminescence in phosphate laser glass.

Opt Lett 2018 Oct;43(19):4823-4826

We report an unusual thermal response of tellurium (Te) near-infrared (NIR) luminescence in phosphate laser glass, where the luminescence first increases and then decreases with heat-treatment temperatures increasing from 250°C to the glass transition temperature (T). This is followed by a distinct revival of Te NIR luminescence at temperatures above T. This result differs from the scenario in conventional rare-earth (Er, Nd, and Yb)-doped phosphate glasses, where the rare-earth NIR emission decreases with increasing heat-treatment temperature. The difference may originate from conversion between Te and other Te species, which depends on the evolution of the glass structure and molecular motion during the reheating processes, leading to unusual thermal response of Te NIR luminescence. The increase in Te clusters enhances Te NIR emission, indicating that Te NIR luminescence is assigned to the Te cluster, in contrast to previous studies. Heating and cooling cycles between 50°C and 250°C reveal strong dependence of the thermal degradation on glass structure. Te-doped phosphate laser glass with zero thermal degradation can be realized by stabilizing NIR luminescence center Te by adjusting the glass structure with reduced network crosslinking. The superior optical performance has been confirmed in our previous study that the NIR luminescence properties can be well maintained in Te-doped fiber. The findings indicate that Te-doped phosphate glass with unusual thermal responses can potentially be used in fiber laser devices.
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http://dx.doi.org/10.1364/OL.43.004823DOI Listing
October 2018

Enabling Computational Design of ZIFs Using ReaxFF.

J Phys Chem B 2018 Oct 9;122(41):9616-9624. Epub 2018 Oct 9.

Department of Materials Science and Metallurgy , University of Cambridge , 27 Charles Babbage Road , Cambridge CB3 0FS , U.K.

Classical force fields have been broadly used in studies of metal-organic framework crystals. However, processes involving bond breaking or forming are prohibited due to the nonreactive nature of the potentials. With emerging trends in the study of zeolitic imidazolate frameworks (ZIFs) that include glass formation, defect engineering, and chemical stability, enhanced computational methods are needed for efficient computational screening of ZIF materials. Here, we present simulations of three ZIF compounds using a ReaxFF reactive force field. By simulating the melt-quench process of ZIF-4, ReaxFF can reproduce the atomic structure, density, thermal properties, and pore morphology of the glass formed ( aZIF-4), showing remarkable agreement with experimental and first-principles molecular dynamics results. The predictive capability of ReaxFF is further exemplified in the melting of ZIF-62, where the balancing of electronic and steric effects of benzimidazolate yields a lower T. On the basis of the electron-withdrawing effect of the -NO group, ReaxFF simulations predict that ZIF-77 has an even lower T in terms of Zn-N interaction, but its low chemical stability makes it unsuitable as a glass former. Because of its low computational cost and transferability, ReaxFF will enable the computational design of ZIF materials by accounting for properties associated with disorder/defects.
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http://dx.doi.org/10.1021/acs.jpcb.8b08094DOI Listing
October 2018

Comment on "Glass Transition, Crystallization of Glass-Forming Melts, and Entropy" 2018, , 103.

Entropy (Basel) 2018 Sep 13;20(9). Epub 2018 Sep 13.

Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.

In a recent article, Schmelzer and Tropin [ , , 103] presented a critique of several aspects of modern glass science, including various features of glass transition and relaxation, crystallization, and the definition of glass itself. We argue that these criticisms are at odds with well-accepted knowledge in the field from both theory and experiments. The objective of this short comment is to clarify several of these issues.
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http://dx.doi.org/10.3390/e20090703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7513222PMC
September 2018

Predicting Q-Speciation in Binary Phosphate Glasses Using Statistical Mechanics.

J Phys Chem B 2018 08 24;122(30):7609-7615. Epub 2018 Jul 24.

Department of Chemistry and Bioscience , Aalborg University , 9220 Aalborg , Denmark.

Predicting the compositional evolution of the atomic-scale structure of oxide glasses is important for developing quantitative composition-property models. In binary phosphate glasses, the addition of network modifiers generally leads to depolymerization of the networks as described by the Q-speciation, where Q denotes PO tetrahedra with n number (between 0 and 3) of bridging P-O-P linkages per tetrahedron. Upon the initial creation of nonbridging oxygens and thus partly depolymerized Q species, a variety of network former-modifier interactions exist. Here, on the basis of P magic angle spinning nuclear magnetic resonance spectroscopy data from the literature, we present a statistical description of the compositional evolution of Q-speciation in these glasses by accounting for the relative enthalpic and entropic contributions to the bonding preferences. We show that the entire glass structure evolution can be predicted based on experimental structural information for only a few glass compositions in each series. The model also captures the differences in bonding preferences in glasses with different field strengths (charge-to-size ratio) of the modifier cations.
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http://dx.doi.org/10.1021/acs.jpcb.8b04604DOI Listing
August 2018

A metal-organic framework with ultrahigh glass-forming ability.

Sci Adv 2018 03 9;4(3):eaao6827. Epub 2018 Mar 9.

State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China.

Glass-forming ability (GFA) is the ability of a liquid to avoid crystallization during cooling. Metal-organic frameworks (MOFs) are a new class of glass formers (-), with hitherto unknown dynamic and thermodynamic properties. We report the discovery of a new series of tetrahedral glass systems, zeolitic imidazolate framework-62 (ZIF-62) [Zn(Im bIm )], which have ultrahigh GFA, superior to any other known glass formers. This ultrahigh GFA is evidenced by a high viscosity η (10 Pa·s) at the melting temperature , a large crystal-glass network density deficit (Δρ/ρ), no crystallization in supercooled region on laboratory time scales, a low fragility ( = 23), an extremely high Poisson's ratio (ν = 0.45), and the highest / ratio (0.84) ever reported. and both increase with benzimidazolate (bIm) content but retain the same ultrahigh / ratio, owing to high steric hindrance and frustrated network dynamics and also to the unusually low enthalpy and entropy typical of the soft and flexible nature of MOFs. On the basis of these versatile properties, we explain the exceptional GFA of the ZIF-62 system.
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http://dx.doi.org/10.1126/sciadv.aao6827DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844704PMC
March 2018

Compositional Dependence of Solubility/Retention of Molybdenum Oxides in Aluminoborosilicate-Based Model Nuclear Waste Glasses.

J Phys Chem B 2018 02 26;122(5):1714-1729. Epub 2018 Jan 26.

Department of Materials Science and Engineering, Rutgers - The State University of New Jersey , Piscataway, New Jersey 08854, United States.

Molybdenum oxides are an integral component of the high-level waste streams being generated from the nuclear reactors in several countries. Although borosilicate glass has been chosen as the baseline waste form by most of the countries to immobilize these waste streams, molybdate oxyanions (MoO) exhibit very low solubility (∼1 mol %) in these glass matrices. In the past three to four decades, several studies describing the compositional and structural dependence of molybdate anions in borosilicate and aluminoborosilicate glasses have been reported in the literature, providing a basis for our understanding of fundamental science that governs the solubility and retention of these species in the nuclear waste glasses. However, there are still several open questions that need to be answered to gain an in-depth understanding of the mechanisms that control the solubility and retention of these oxyanions in glassy waste forms. This article is focused on finding answers to two such questions: (1) What are the solubility and retention limits of MoO in aluminoborosilicate glasses as a function of chemical composition? (2) Why is there a considerable increase in the solubility of MoO with incorporation of rare-earth oxides (for example, NdO) in aluminoborosilicate glasses? Accordingly, three different series of aluminoborosilicate glasses (compositional complexity being added in a tiered approach) with varying MoO concentrations have been synthesized and characterized for their ability to accommodate molybdate ions in their structure (solubility) and as a glass-ceramic (retention). The contradictory viewpoints (between different research groups) pertaining to the impact of rare-earth cations on the structure of aluminoborosilicate glasses are discussed, and their implications on the solubility of MoO in these glasses are evaluated. A novel hypothesis explaining the mechanism governing the solubility of MoO in rare-earth containing aluminoborosilicate glasses has been proposed.
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http://dx.doi.org/10.1021/acs.jpcb.7b09158DOI Listing
February 2018

Thermometer Effect: Origin of the Mixed Alkali Effect in Glass Relaxation.

Phys Rev Lett 2017 Sep 31;119(9):095501. Epub 2017 Aug 31.

Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095, USA.

Despite the dramatic increase of viscosity as temperature decreases, some glasses are known to feature room-temperature relaxation. However, the structural origin of this phenomenon-known as the "thermometer effect"-remains unclear. Here, based on accelerated molecular dynamics simulations of alkali silicate glasses, we show that both enthalpy and volume follow stretched exponential decay functions upon relaxation. However, we observe a bifurcation of their stretching exponents, with β=3/5 and 3/7 for enthalpy and volume relaxation, respectively, in agreement with Phillips's topological diffusion-trap model. Based on these results, we demonstrate that the thermometer effect is a manifestation of the mixed alkali effect. We show that relaxation is driven by the existence of stressed local structural instabilities in mixed alkali glasses. This driving force is found to be at a maximum when the concentrations of each alkali atom equal each other, which arises from a balance between the concentration of each alkali atom and the magnitude of the local stress that they experience.
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http://dx.doi.org/10.1103/PhysRevLett.119.095501DOI Listing
September 2017

Computational approaches for investigating interfacial adhesion phenomena of polyimide on silica glass.

Sci Rep 2017 09 5;7(1):10475. Epub 2017 Sep 5.

Platform Technology Lab, Samsung Advanced Institute of Technology, 130 Samsung-ro, Suwon, Gyeonggi-do, 443-803, Republic of Korea.

This manuscript provides a comprehensive study of adhesion behavior and its governing mechanisms when polyimide undergoes various modes of detachment from silica glass. Within the framework of steered molecular dynamics, we develop three different adhesion measurement techniques: pulling, peeling, and sliding. Such computational methodologies can be applied to investigate heterogeneous materials with differing interfacial adhesion modes. Here, a novel hybrid potential involving a combination of the INTERFACE force field in conjunction with ReaxFF and including Coulombic and Lennard-Jones interactions is employed to study such interfaces. The studies indicate that the pulling test requires the largest force and the shortest distance to detachment as the interfacial area is separated instantaneously, while the peeling test is observed to exhibit the largest distance for detachment because it separates via line-by-line adhesion. Two kinds of polyimides, aromatic and aliphatic type, are considered to demonstrate the rigidity dependent adhesion properties. The aromatic polyimide, which is more rigid due to the stronger charge transfer complex between chains, requires a greater force but a smaller distance at detachment than the aliphatic polyimide for all of the three methodologies.
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http://dx.doi.org/10.1038/s41598-017-10994-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5585183PMC
September 2017

Cooling rate effects in sodium silicate glasses: Bridging the gap between molecular dynamics simulations and experiments.

J Chem Phys 2017 Aug;147(7):074501

Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), University of California, Los Angeles, California 90095-1593, USA.

Although molecular dynamics (MD) simulations are commonly used to predict the structure and properties of glasses, they are intrinsically limited to short time scales, necessitating the use of fast cooling rates. It is therefore challenging to compare results from MD simulations to experimental results for glasses cooled on typical laboratory time scales. Based on MD simulations of a sodium silicate glass with varying cooling rate (from 0.01 to 100 K/ps), here we show that thermal history primarily affects the medium-range order structure, while the short-range order is largely unaffected over the range of cooling rates simulated. This results in a decoupling between the enthalpy and volume relaxation functions, where the enthalpy quickly plateaus as the cooling rate decreases, whereas density exhibits a slower relaxation. Finally, we show that, using the proper extrapolation method, the outcomes of MD simulations can be meaningfully compared to experimental values when extrapolated to slower cooling rates.
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http://dx.doi.org/10.1063/1.4998611DOI Listing
August 2017

Accessing Forbidden Glass Regimes through High-Pressure Sub-T Annealing.

Sci Rep 2017 04 18;7:46631. Epub 2017 Apr 18.

Department of Chemistry and Bioscience, Aalborg University, Aalborg 9220, Denmark.

Density and hardness of glasses are known to increase upon both compression at the glass transition temperature (T) and ambient pressure sub-T annealing. However, a serial combination of the two methods does not result in higher density and hardness, since the effect of compression is countered by subsequent annealing and vice versa. In this study, we circumvent this by introducing a novel treatment protocol that enables the preparation of high-density, high-hardness bulk aluminosilicate glasses. This is done by first compressing a sodium-magnesium aluminosilicate glass at 1 GPa at T, followed by sub-T annealing in-situ at 1 GPa. Through density, hardness, and heat capacity measurements, we demonstrate that the effects of hot compression and sub-T annealing can be combined to access a "forbidden glass" regime that is inaccessible through thermal history or pressure history variation alone. We also study the relaxation behavior of the densified samples during subsequent ambient pressure sub-T annealing. Density and hardness are found to relax and approach their ambient condition values upon annealing, but the difference in relaxation time of density and hardness, which is usually observed for hot compressed glasses, vanishes for samples previously subjected to high-pressure sub-T annealing. This confirms the unique configurational state of these glasses.
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http://dx.doi.org/10.1038/srep46631DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5394531PMC
April 2017

Variability in the relaxation behavior of glass: Impact of thermal history fluctuations and fragility.

J Chem Phys 2017 Feb;146(7):074504

School of Materials Science and Engineering, Qilu University of Technology, Jinan, Shandong, China.

Glasses are nonequilibrium materials that continuously relax toward the metastable supercooled liquid state. As such, the properties of a glass depend on both its composition and thermal history. When an initially cooled glass is subjected to additional thermal cycles, relaxation during the heat treatment is accelerated, leading to changes in the macroscopic properties of the glass. This relaxation behavior is intrinsic to the glassy state and of critical interest to the high-tech glass industry. In many practical cases, the magnitude of the relaxation is less important than the variability of the relaxation effects due to slight variations in the thermal history experienced by the glass. These fluctuations in thermal history can occur either during the initial glass formation or during the subsequent heat treatment cycle(s). Here we calculate the variation in relaxation behavior using a detailed enthalpy landscape model, showing that the relaxation variability can be reduced dramatically by increasing the fragility of the system.
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http://dx.doi.org/10.1063/1.4975760DOI Listing
February 2017

Crack nucleation criterion and its application to impact indentation in glasses.

Sci Rep 2016 Apr 15;6:23720. Epub 2016 Apr 15.

Science and Technology Division, Corning Incorporated, Corning, New York 14831, USA.

Molecular dynamics (MD) simulations are used to directly observe nucleation of median cracks in oxide glasses under indentation. Indenters with sharp angles can nucleate median cracks in samples with no pre-existing flaws, while indenters with larger indenter angles cannot. Increasing the tip radius increases the critical load for nucleation of the median crack. Based upon an independent set of simulations under homogeneous loading, the fracture criterion in the domain of the principal stresses is constructed. The fracture criterion, or "fracture locus", can quantitatively explain the observed effects of indenter angle and indenter tip radius on median crack nucleation. Our simulations suggest that beyond the maximum principal stress, plasticity and multi-axial stresses should also be considered for crack nucleation under indentation, even for brittle glassy systems.
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http://dx.doi.org/10.1038/srep23720DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4832188PMC
April 2016

Linking Equilibrium and Nonequilibrium Dynamics in Glass-Forming Systems.

J Phys Chem B 2016 Mar 18;120(12):3226-31. Epub 2016 Mar 18.

Science and Technology Division, Corning Incorporated , Corning, New York 14831, United States.

Understanding nonequilibrium glassy dynamics is of great scientific and technological importance. However, prediction of the temperature, thermal history, and composition dependence of nonequilibrium viscosity is challenging due to the noncrystalline and nonergodic nature of the glassy state. Here, we show that the nonequilibrium glassy dynamics are intimately connected with the equilibrium liquid dynamics. This is accomplished by deriving a new functional form for the thermal history dependence of nonequilibrium viscosity, which is validated against experimental measurements of industrial silicate glasses and computed viscosities for selenium over a wide range of conditions. Since the temperature and composition dependence of liquid viscosity can be predicted using temperature-dependent constraint theory, our work also opens the possibility to improve understanding of the physics of nonequilibrium viscosity.
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http://dx.doi.org/10.1021/acs.jpcb.6b00141DOI Listing
March 2016
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