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Showing papers on "Glass transition published in 2014"


Journal ArticleDOI
TL;DR: In this article, the authors discuss recent experiments that directly measure mobility at or near the surface of glassy polymers and indicate that enhanced mobility near the free surface can exceed bulk mobility by several orders of magnitude and extend for several nanometers into the bulk polymer.
Abstract: The past 20 years have seen a substantial effort to understand dynamics and the glass transition in thin polymer films. In this Perspective, we consider developments in this field and offer a consistent interpretation of some major findings. We discuss recent experiments that directly measure mobility at or near the surface of glassy polymers. These experiments indicate that enhanced mobility near the free surface can exceed bulk mobility by several orders of magnitude and extend for several nanometers into the bulk polymer. Enhanced mobility near the free surface allows a qualitative understanding of many of the observations of a reduced glass transition temperature Tg in thin films. For thin films, knowledge of Tg by itself is less useful than for bulk materials. Because of this, new experimental methods that directly measure important material properties are being developed.

437 citations


Journal ArticleDOI
TL;DR: In this article, the effects of modified boron nitride (h-BN) content on the thermal and insulating properties of epoxy/BN composites were investigated, and it was found that incorporation of h-BN particles in the epoxy matrix significantly enhanced the thermal conductivity of the composites.
Abstract: Hexagonal boron nitride (h-BN) microparticles, modified by surface coupling agent 3-aminopropyl triethoxy silane (APTES), were used to fabricate thermally conductive epoxy/BN composites, and the effects of modified-BN content on the thermal and insulating properties were investigated. It was found that incorporation of h-BN particles in the epoxy matrix significantly enhanced the thermal conductivity of the composites. With 30 wt% modified-BN loading, the thermal conductivity of the composites was 1.178 W m−1 K−1, 6.14 times higher than that of the neat epoxy. Fabricated epoxy/BN composites exhibited improved thermal stability, storage modulus, and glass transition temperature with increased BN content. The composites also possessed excellent electrical insulation properties. These results revealed that epoxy/BN composites are promising as efficient heat-releasing materials for thermal management and microelectronic encapsulation.

258 citations


Journal ArticleDOI
TL;DR: In this article, the static and dynamic properties of poly(2-vinylpyridine)/silica nanocomposites are investigated by temperature modulated differential scanning calorimetry, broadband dielectric spectroscopy (BDS), small-angle X-ray scattering (SAXS), and transmission electron microscopy.
Abstract: The static and dynamic properties of poly(2-vinylpyridine)/silica nanocomposites are investigated by temperature modulated differential scanning calorimetry, broadband dielectric spectroscopy (BDS), small-angle X-ray scattering (SAXS), and transmission electron microscopy. Both BDS and SAXS detect the existence of an interfacial polymer layer on the surface of nanoparticles. The results show that whereas the calorimetric glass transition temperature varies only weakly with nanoparticle loading, the segmental mobility of the polymer interfacial layer is slower than the bulk polymer by 2 orders of magnitude. Detailed analysis of BDS and SAXS data reveal that the interfacial layer has a thickness of 4–6 nm irrespective of the nanoparticle concentration. These results demonstrate that in contrast to some recent articles on polymer nanocomposites, the interfacial polymer layer is by no means a “dead layer”. However, its existence might provide some explanation for controversies surrounding the dynamics of poly...

241 citations


Journal ArticleDOI
TL;DR: In this article, the main and secondary relaxations of metallic glasses are analyzed and the correlation between the atomic mobility and the thermo-mechanical treatments in metallic glasses is analyzed.

228 citations


Journal ArticleDOI
28 Feb 2014-Science
TL;DR: The experiments and model provide a measure of surface mobility in a simple geometry where confinement and substrate effects are negligible and fine control of the glassy rheology is of key interest to nanolithography among numerous other applications.
Abstract: Thin polymer films have striking dynamical properties that differ from their bulk counterparts. With the simple geometry of a stepped polymer film on a substrate, we probe mobility above and below the glass transition temperature Tg. Above Tg the entire film flows, whereas below Tg only the near-surface region responds to the excess interfacial energy. An analytical thin-film model for flow limited to the free surface region shows excellent agreement with sub-Tg data. The system transitions from whole-film flow to surface localized flow over a narrow temperature region near the bulk Tg. The experiments and model provide a measure of surface mobility in a simple geometry where confinement and substrate effects are negligible. This fine control of the glassy rheology is of key interest to nanolithography among numerous other applications.

208 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigate how dynamic behavior of functional poly(n-butyl acrylate) melts and cross-linked networks is influenced by different hydrogen-bonding side groups.
Abstract: Polymers containing hydrogen-bonding side groups (HBGs) can form transient supramolecular networks that exhibit technologically useful viscoelastic properties. Here, we investigate how dynamic behavior of functional poly(n-butyl acrylate) melts and cross-linked networks is influenced by different HBGs. Random copolymers containing weak and strong HBGs were synthesized and subjected to thermal and dynamic mechanical analysis. The glass transition temperature (Tg) increased nearly linearly with the HBG concentration, and this effect was similar for both weak and strong binding groups. Copolymers containing weak HBGs behaved as unentangled melts and exhibited higher storage and loss modulus with increasing amounts of binding group. In contrast, copolymers containing strong HBGs behaved like entangled networks. Flow activation energies increased linearly with comonomer content; and, for weak hydrogen-bonding groups, they depended only on the departure from Tg. Similar behavior was observed in cross-linked fil...

187 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the role change of Na+ cations from network modifier to charge compensator in the presence of Al3+ ions and showed that the configuration entropy of the configurational entropy at the glass transition temperature is strongly nonlinear, with sharp increases and decreases depending on the Al/(Al+Na) ratio.

173 citations


Journal ArticleDOI
TL;DR: It is demonstrated from a study of several metallic glass-forming liquids that the rate of this structural ordering as a function of temperature correlates with the kinetic fragility of the liquid, demonstrating a structural basis for fragility.
Abstract: Glass fragility characterises the rate of change in viscosity as a liquid is cooled towards the glass transition temperature. Here, the authors demonstrate via neutron diffraction that the rate at which structural ordering occurs within the melt correlates with kinetic fragility in a range of metallic glass samples.

170 citations


Journal ArticleDOI
TL;DR: In this paper, a molecular-level understanding of dynamics in imidazolium-based ionomers with different counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS).
Abstract: A molecular-level understanding of dynamics in imidazolium-based ionomers with different counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS). Variations of the counterion size and side chain length lead to changes in glass transition temperature (Tg), extent of ionic aggregation, and dielectric constant, with consequences for ion transport. A physical model of electrode polarization is used to determine the number density of simultaneously conducting ions and their mobility. Imidazolium-based ionomers with larger counterion and longer side chain have lower Tg, resulting in higher ionic conductivity and mobility. The ionic mobility is coupled to ion motions that are directly measured as a second segmental process in DRS, as these are observed to share the same Vogel temperature. Time–temperature superposition (tTS) was applied to create linear viscoelasticity master curves and to investigate the delay in chain motion re...

169 citations


Journal ArticleDOI
TL;DR: In this article, a series of rigid, bulky triptycene-based diamine monomers were designed, synthesized, and subsequently incorporated into the backbone of polyimides via polycondensation with 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) to obtain a series polyimide membranes with high fractional free volume.
Abstract: Robust polymer membranes that are highly permeable and selective are desired for energy efficient gas separation processes. In this study, a series of rigid, bulky triptycene-based diamine monomers were designed, synthesized, and subsequently incorporated into the backbone of polyimides via polycondensation with 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) to obtain a series of polyimide membranes with high fractional free volume. These triptycene-containing polyimides with systematic variations in their chemical structure demonstrate the viability of the ‘tunable’ fractional free volume by introducing various substituents onto the polymer backbone. All the polyimides synthesized exhibited film-forming high molecular weight, high solubility, and excellent thermal properties, with glass transition temperatures ranging from 280 °C to 300 °C and thermal stability up to 500 °C. Compared to other classes of glassy polymers, these triptycene-polyimides had high combinations of permeability and selectivity, suggesting that a favorable free volume size distribution in these triptycene polyimides was induced by the unique chain packing mechanism of triptycene units. The correlation between gas transport properties and the polymer chemical structure was also investigated. Altering the size of the substituents neighboring the triptycene units provides greater opportunity to fine-tune the fractional free volume and free volume size distribution in the polymer, which in turn can change the transport properties effectively to meet various separation needs. It is expected that additional design modifications made by exploiting the chemistry versatility of the triptycene moiety and by selectively adding other components may improve these membranes to break the gas permeability–selectivity trade-off barrier.

165 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of polymer crystallization on ion transport is decoupled by designing and fabricating a model polymer single crystal electrolyte system with controlled crystal structure, size, crystallinity, and orientation.
Abstract: Polymer electrolytes have attracted intensive attention due to their potential applications in all-solid-state lithium batteries. Ion conduction in this system is generally considered to be confined in the amorphous polymer/ion phase, where segmental relaxation of the polymer above glass transition temperature facilitates ion transport. In this article, we show quantitatively that the effect of polymer crystallization on ion transport is twofold: structural (tortuosity) and dynamic (tethered chain confinement). We decouple these two effects by designing and fabricating a model polymer single crystal electrolyte system with controlled crystal structure, size, crystallinity, and orientation. Ion conduction is confined within the chain fold region and guided by the crystalline lamellae. We show that, at low content, due to the tortuosity effect, the in-plane conductivity is 2000 times greater than through-plane one. Contradictory to the general view, the dynamic effect is negligible at moderate ion contents....

Journal ArticleDOI
TL;DR: In this paper, the mesoporous metal organic framework (MOF) Fe(BTC) in a Matrimid®-PI matrix was characterized in terms of their carbon dioxide (CO2) and methane (CH4) separation performance at low and high pressures.

Journal ArticleDOI
TL;DR: In this paper, the authors have shown that ZnO acts as a network modifier with BiO6 octahedral structural units for glass samples with x = 5, 10, and 15.

Journal ArticleDOI
Naisheng Jiang1, Jun Shang1, Xiaoyu Di1, Maya K. Endoh1, Tadanori Koga1 
TL;DR: In this article, three different homopolymers (polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate), which have similar inherent stiffness and bulk glass transition temperature (Tg), but have different affinities with Si substrates, were chosen as models.
Abstract: Thermal annealing is one of the most indispensable polymer fabrication processes and plays essential roles in controlling morphologies and properties of polymeric materials. We here report that thermal annealing also facilitates polymer adsorption from the melt on planar silicon (Si) substrates, resulting in the formation of a high-density polymer nanolayer with flattened chain confirmations. Three different homopolymers (polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate)), which have similar inherent stiffness and bulk glass transition temperature (Tg), but have different affinities with Si substrates, were chosen as models. Spin-cast films (∼50 nm in thickness) with the three polymers were prepared on cleaned Si substrates and then placed in a vacuum oven set at a temperature far above the bulk Tg. In order to monitor the polymer adsorption process at the solid-polymer melt interface during thermal annealing, we used the protocol that combines vitrification of the annealed films (via rapi...

Journal ArticleDOI
TL;DR: In this article, reduced graphene oxide (RGO)-encapsulated SiO2 hybrids (SiO2@RGO) were fabricated from the thermal reduction of electrostatically assembled SiO 2@GO hybrids.
Abstract: Reduced graphene oxide (RGO)-encapsulated SiO2 hybrids (SiO2@RGO) were fabricated from the thermal reduction of electrostatically assembled SiO2@GO hybrids. Then, epoxy composites, filled with SiO2, SiO2@GO and SiO2@RGO hybrids, were prepared by a solvent-free curing process, and their thermal, dielectric and thermo-mechanical properties were investigated and compared. In the SiO2@RGO/epoxy composites, the mono-dispersed SiO2 nanoparticles are firmly embedded in the thin layer of RGO nanosheets, forming unique core–shell nanostructures that effectively prevent the aggregation of RGO nanosheets in the polymer matrix, construct conductive pathways at the particle–polymer interface and afford the epoxy composites with outstanding thermo-mechanical properties. The dielectric properties of the SiO2@RGO/epoxy composites exhibit a typical percolation transition near 0.174 vol% for RGO (20 wt% of SiO2@RGO hybrids), where the dielectric constant could reach 77.23 at 1 kHz, which is 22 times that of the neat epoxy resin. Upon further increase of the loading content, the gradual contact of the filler particles leads to the formation of interfacial continuous conductive networks, and both the thermal conductivity and dielectric constant of the composites show a dramatic increase. With a filler loading of 40 wt% SiO2@RGO (0.373 vol% for RGO), a thermal conductivity of 0.452 W m−1 K−1 is obtained, which is two times larger than that of neat epoxy. In addition, SiO2@RGO/epoxy composites reveal significantly decreased coefficient of thermal expansion (CTE) and increased glass transition temperature (Tg). We believe this special core–shell SiO2@RGO structure, with its inner mechanically enhanced inorganic particles and outer interfacial conductive phase, could make full use of the enhancement effect of different components and thus endow the polymer composites with outstanding properties overall.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a phase diagram model to predict the structural units of glass with mutually miscible or immiscible phases based on infrared spectroscopy, Raman and nuclear magnetic resonance (NMR) measurements.

Journal ArticleDOI
TL;DR: In this review, the peculiarities of the thermodynamics and dynamics of glass-forming polymers are discussed, with particular emphasis on those topics currently the subject of debate.
Abstract: The fate of matter when decreasing the temperature at constant pressure is that of passing from gas to liquid and, subsequently, from liquid to crystal. However, a class of materials can exist in an amorphous phase below the melting temperature. On cooling such materials, a glass is formed; that is, a material with the rigidity of a solid but exhibiting no long-range order. The study of the thermodynamics and dynamics of glass-forming systems is the subject of continuous research. Within the wide variety of glass formers, an important sub-class is represented by glass forming polymers. The presence of chain connectivity and, in some cases, conformational disorder are unfavourable factors from the point of view of crystallization. Furthermore, many of them, such as amorphous thermoplastics, thermosets and rubbers, are widely employed in many applications. In this review, the peculiarities of the thermodynamics and dynamics of glass-forming polymers are discussed, with particular emphasis on those topics currently the subject of debate. In particular, the following aspects will be reviewed in the present work: (i) the connection between the pronounced slowing down of glassy dynamics on cooling towards the glass transition temperature (Tg) and the thermodynamics; and, (ii) the fate of the dynamics and thermodynamics below Tg. Both aspects are reviewed in light of the possible presence of a singularity at a finite temperature with diverging relaxation time and zero configurational entropy. In this context, the specificity of glass-forming polymers is emphasized.

Journal ArticleDOI
TL;DR: In this paper, the relationship between glass structure and tensile behavior across a wide range of structural states was investigated using ion irradiation of thermoplastically molded Pt57.5Cu14.3Ni5.7P22.5 metallic glass nanowires.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs).
Abstract: Charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) are investigated by a combination of broadband dielectric spectroscopy, dynamic mechanical spectroscopy and differential scanning calorimetry. While the dc conductivity and fluidity exhibit practically identical temperature dependence for the non-polymerized IL, a significant decoupling of ionic conduction from structural dynamics is observed for the polymerized IL. In addition, the dc conductivity of the polymerized IL exceeds that of its molecular counterpart by four orders of magnitude at their respective calorimetric glass transition temperatures. This is attributed to the unusually high mobility of the anions especially at lower temperatures when the structural dynamics is significantly slowed down. A simple physical explanation of the possible origin of the remarkable decoupling of ionic conductivity from structural dynamics is proposed.

Journal ArticleDOI
TL;DR: In this paper, the nucleation efficiency of multiwall carbon nanotubes (MWCNT) in poly(e-caprolactone) (PCL) was tested for a wide range of temperatures and cooling rates and compared to the efficiency of homogeneously formed nuclei.

Journal ArticleDOI
TL;DR: In this article, the authors reported the dramatic deviation of glass transition behaviors of poly(methyl methacrylate) (PMMA) confined in cylindrical nanopores with diameter significantly larger than chain's radius of gyration (Rg).
Abstract: Recently, confinement of polymers with different geometries has become a research hotspot. Here, we report the dramatic deviation of glass transition behaviors of poly(methyl methacrylate) (PMMA) confined in cylindrical nanopores with diameter significantly larger than chain’s radius of gyration (Rg). Fast cooling a PMMA melt in the nanopores results in a glass with one single glass transition temperature (Tg). But two distinct Tgs are detected after slow cooling the melt. The deviation in Tg could be as large as 45 K. This phenomenon is interpreted by a two-layer model. During vitrification under slow cooling two distinct layers are formed: a strongly constrained interfacial layer showing an increased Tg as compared to that of the bulk polymer and a core with a decreased Tg. By thermal annealing experiments, we find that these two Tgs are inherently correlated. In addition, the deviation of Tg for PMMA confined in nanopores reveals a dependence on molecular weight.

Journal ArticleDOI
TL;DR: In this article, the effect of the addition of graphene on the glass transition temperature (Tg) of polymers was investigated, first with poly(methyl methacrylate) and then with an extensive literature review.
Abstract: The effect of the addition of graphene on the glass transition temperature (Tg) of polymers was investigated, first with poly(methyl methacrylate) and then with an extensive literature review. Isotactic (i-PMMA) and atactic PMMA (a-PMMA) were blended with pristine graphene (PG) and thermally reduced graphene (TRG). A Tg increase was found for a-PMMA nanocomposites made via in situ polymerization with TRG but not when a-PMMA was solvent blended with TRG. However, a Tg increase was found for TRG solvent blended into i-PMMA and a smaller increase for PG with i-PMMA. Nearly all the increase occurred at the lowest loading, 0.25 wt %, with little change at increased graphene concentration. Tg increases due to interfacial interactions between matrix polymers and fillers. Physical blending such as solvent processes cannot provide enough interaction at the interfaces, whereas chemical blending processes such as in situ polymerization can yield strong covalent bonds. However, i-PMMA molecules can align on graphene ...

Journal ArticleDOI
TL;DR: This work shows that to quantitatively understand stability at a microscopic level, the presence of weakly interacting pairs of particles must be included, and predicts various nontrivial scaling behavior of the elasticity and vibrational properties of colloidal glasses that can be tested experimentally.
Abstract: How a liquid becomes rigid at the glass transition is a central problem in condensed matter physics. In many scenarios of the glass transition, liquids go through a critical temperature below which minima of free energy appear. However, even in the simplest glass, hard spheres, what confers mechanical stability at large density is highly debated. In this work we show that to quantitatively understand stability at a microscopic level, the presence of weakly interacting pairs of particles must be included. This approach allows us to predict various nontrivial scaling behavior of the elasticity and vibrational properties of colloidal glasses that can be tested experimentally. It also gives a spatial interpretation to recent, exact calculations in infinite dimensions.

Journal ArticleDOI
TL;DR: In this article, the authors derived the detailed expression of stress relaxation time, which reveals an Arrhenius type dependency of material relaxation behavior on the applied temperature, and determined the energy barrier for the BERs in different networks.
Abstract: Thermally malleable polymers which undergo covalent bond exchange reactions (BERs) have been shown to be able to rearrange their network topology at high temperatures without impairing the network integrity. At low temperatures, the BERs are so sluggish that the materials behave like traditional thermosetting polymers. In this paper, we demonstrated that the temperature dependent BER rate could be tuned by adjusting the stoichiometry of monomers. As the ratio of hard segments in the epoxy thermoset network is increased, the material's glass transition temperature (Tg) is increased, with a corresponding increase in the temperature required to achieve a given stress relaxation rate. The material stress relaxation behavior was studied from both a theoretical and experimental point of view. Based on the kinetics of BERs, we derived the detailed expression of stress relaxation time, which reveals an Arrhenius type dependency of material relaxation behavior on the applied temperature. Subsequently, from the experimental stress relaxation curves, we determined the energy barrier for the BERs in different networks. With the Tg being elevated from 30.3 °C to 63.0 °C, the BER energy barrier is linearly increased from 68.2 kJ mol−1 to 97.3 kJ mol−1. Such a correlation between these two thermomechanical behaviors provides an additional design parameter (beyond catalyst choice) which can aid in achieving highly tunable service conditions for practical engineering applications of thermally malleable thermosets.

Journal ArticleDOI
TL;DR: In this article, NH2-MIL 53 was used to fabricate a mixed matrix membrane (MMM) and various characterization methods as well as a series of CO2/CH4 gas separation tests (i.e. pure and mixed gas tests) were conducted in order to determine the effect of NH2MIL53 on the properties of the prepared MMMs and their gas transport characteristics.
Abstract: Poly(4-methyl-1-pentyne) (PMP) as a polymer matrix together with synthesized NH2-MIL 53 metal organic framework (MOF) as a filler were used to fabricate a mixed matrix membrane (MMM). Various characterization methods as well as a series of CO2/CH4 gas separation tests (i.e. pure and mixed gas tests) were conducted in order to determine the effect of NH2-MIL 53 on the properties of the prepared MMMs and their gas transport characteristics. The results of TGA and DMA showed that both degradation temperature (Td) and glass transition temperature (Tg) increased by increasing the NH2-MIL 53 loading. SEM images also demonstrated that uniform dispersion of NH2-MIL 53 particles in the PMP matrix was achieved with no noticeable voids in the polymer-filler interfaces. It was also found that incorporation of NH2-MIL 53 in PMP results in an increase of gas permeability (especially for CO2) and higher CO2/CH4 selectivity. In contrast with the increment of CO2 solubility due to the presence of MOF in the polymer matrix, the solubility of CH4 decreases. Although the CO2 solubility was improved with the addition of NH2-MIL 53, its diffusivity remained almost constant with no significant changes. Lastly, it was observed that increasing the MOF loading along with higher feed pressure provide a condition to overcome the Robeson upper bound.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the dynamics of gold nanoparticles within an entangled liquid of poly(n-butyl methacrylate) (PBMA) above the glass transition temperature (Tg).
Abstract: We investigated the dynamics of gold nanoparticles (NPs) within an entangled liquid of poly(n-butyl methacrylate) (PBMA) above the glass transition temperature (Tg). The experiments were performed by using a modified version of fluctuation correlation spectroscopy (FCS), which measured the translational diffusion (D) of the isolated NPs as a function of their size (2R0 = 5–20 nm) and temperature (T). We probed the most interesting but sparsely investigated length regime where the particle size/tube diameter (dt) ratio ranges between ∼1–4. This allowed us to put into direct test recently developed theories and simulations. By measuring the bulk viscosity of the melt, the ratio D/DSE was determined, where DSE is the continuum prediction from Stokes–Einstein (SE) relation. Our results indicate gradual recovery to SE behavior and full coupling to entanglement relaxation would require 2R0 ≈ 7–10dt.

Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of various statistical mechanical descriptions of the glassy state and their practical use in understanding glass physics and in the design of new glass compositions.
Abstract: The field of glass science is quickly maturing from a purely empirical science to one built upon rigorous fundamental physics. These advancements offer an unprecedented level of understanding of the glass transition and the glassy state, as well as the ability to design new glass compositions starting at the atomic level. As a nonequilibrium material, the structure and properties of glass depend not only on its composition, but also on its thermal and pressure histories. Since glass is thermodynamically unstable, it is continually relaxing toward the metastable supercooled liquid state. Owing to this time dependence of glass properties and microstructure, traditional reversible thermodynamics cannot be directly applied to study the glassy state. While some nonequilibrium aspects of the glassy state can be estimated using irreversible thermodynamics, this approach has no microscopic basis and hence cannot offer a rigorous physical description of either the glass transition or glass itself. Alternatively, nonequilibrium statistical mechanics offers a framework in which the macroscopic properties of a glass can be rigorously calculated from its microscopic structure. As such, statistical mechanics has many practical applications in glass science and technology. The objective of this article is to provide an overview of various statistical mechanical descriptions of the glassy state and their practical use in understanding glass physics and in the design of new glass compositions. The relationship among these various descriptions is emphasized to build a single unified picture of glass statistical mechanics synthesizing these various approaches.

Journal ArticleDOI
TL;DR: In this paper, the effects of WO 3 concentration on the structural, thermal and optical properties of tellurite glasses have been discussed, and the results show an important decrease of the optical band gap with the increase of W o 3 concentration.
Abstract: Tellurite glasses with the molar composition (89-x) TeO 2 –10TiO 2 –1Nd 2 O 3 –xWO 3 (x = 0, 10 and 20 mol%) were prepared by the conventional melt-quenching technique. The effects of WO 3 concentration on the structural, thermal and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry measurements, thermal properties such as glass transition temperature T g , crystallization temperature T x , and thermal stability ΔT are estimated. It was found that ΔT increases with the increase of WO 3 composition which can indicate a reinforcement of the glassy network. Both Raman and FTIR results show that the addition of WO 3 induced a depolymerisation of tellurite glass since the Te–O–Te inter-chain linkages are progressively substituted by stronger Te–O–W bridges that are at the origin of the increase of the thermal stability of the glass. The optical band gap energy values corresponding to the direct and indirect allowed transitions and the Urbach energy values of the prepared tellurite glasses have been calculated from optical absorption edges. The results show an important decrease of the optical band gap with the increase of WO 3 concentration. It was assigned to W 6 + ions that could have a role as network modifier. The Urbach energy was found to decrease with WO 3 compositions which suggest the possibility of long range order. The refractive index and extinction coefficient were obtained by spectroscopic ellipsometry. Higher values for the refractive index are recorded due to the high polarizability of non-bridging oxygen. It is observed also that the refractive index, n increases with increasing WO 3 content. It is established that there is a trend by which the energy gap decreases with increasing refractive index and increasing the polarizability of the oxide ions. The complex dielectric function e, relative to each sample, was estimated from regression analysis. The material studied here has potential application as optical fiber.

Journal ArticleDOI
Haiyan Ding1, Yang Shao1, Pan Gong1, Jing-Feng Li1, Kefu Yao1 
TL;DR: In this article, a high-entropy bulk metallic glass (HE-BMG) with a critical diameter larger than 15mm has been successfully prepared by copper mold casting, and it showed that newly developed HE-BMGs possess large glass-forming ability, together with the supercooled liquid region Δ T (= T x − T g ), reduced glass transition temperature T rg (= T g / T l ) and γ parameter (=T x /( T g + T l )) of 70 K, 0.619 and 0.422, respectively.

Journal ArticleDOI
TL;DR: In this article, the structural properties of barium vanadophophosphate glass were investigated using XPS and FTIR spectroscopy, and it was found that the O1s, P2p, and V2p core level spectra indicate the presence of primarily P−O−P, P-O−V and V−O-V structural bonds, and more than one valence state of V ions being present.