Showing papers on "Glass transition published in 2004"
TL;DR: In this article, a roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
Abstract: Ionic liquids are good solvents for catalytic reactions. The rational selection of the appropriate ionic liquid solvent for a particular reaction requires general knowledge of the properties of ionic liquids, and the details of some properties of the specific ionic liquid solvents being considered. The solvent properties of ionic liquids that are relevant to catalysis are discussed, and sources of the values of those properties for ionic liquids are identified. A roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
745 citations
TL;DR: The compositional dependence of a glass-forming ability was systematically studied in a binary alloy series Cu100−xZrx (x=34, 36, 38.2, 40 at%) by the copper mold casting method.
548 citations
TL;DR: The discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods are reported, which showed interesting physical, magnetic, and mechanical properties, along with high thermal stability.
Abstract: Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist's dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.
537 citations
TL;DR: In this paper, the role of Y/Ln as a fluxing agent is relatively small in terms of glass formability enhancement, and the obtained bulk metallic glasses are non-ferromagnetic and exhibit high elastic moduli of approximately 180-200 GPa and microhardness of approximately 13 GPa.
Abstract: Fe–Cr–Mo–(Y,Ln)–C–B bulk metallic glasses (Ln are lanthanides) with maximum diameter thicknesses reaching 12 mm have been obtained by casting. The high glass formability is attained despite a low reduced glass transition temperature of 0.58. The inclusion of Y/Ln is motivated by the idea that elements with large atomic sizes can destabilize the competing crystalline phase, enabling the amorphous phase to be formed. It is found that the role of Y/Ln as a fluxing agent is relatively small in terms of glass formability enhancement. The obtained bulk metallic glasses are non-ferromagnetic and exhibit high elastic moduli of approximately 180–200 GPa and microhardness of approximately 13 GPa.
516 citations
TL;DR: This minireview describes the physics associated with the preparation and storage of amorphous solids including a review of the common theories of the glass transition and relaxation processes.
483 citations
TL;DR: In this article, the authors demonstrate that simple binary bulk amorphous alloys can be obtained by copper mold casting even in a binary metallic system, using the Cu-Zr model system, and demonstrate that the narrow, off-eutectic, bulk-glass-forming range was found to require composition pinpointing to < 1 at.
Abstract: Using the Cu–Zr model system, we demonstrate that bulk amorphous alloys can be obtained by copper mold casting even in a binary metallic system. The narrow, off-eutectic, bulk-glass-forming range was found to require composition pinpointing to <1 at. %. A phase selection diagram is used to explain the success of our microstructure-based approach to pinpoint the best glass former in a given system. The implications of discovering simple binary bulk amorphous alloys are discussed, in terms of its impact on understanding the formation and physics of bulk metallic glasses.
465 citations
TL;DR: It is shown that the fragility of a glass-forming liquid is intimately linked to a very basic property of the corresponding glass phase: the relative strength of shear and bulk moduli, or Poisson's ratio.
Abstract: The nature of the transformation by which a supercooled liquid ‘freezes’ to a glass—the glass transition—is a central issue in condensed matter physics1,2,3 but also affects many other fields, including biology4. Substantial progress has been made in understanding this phenomenon over the past two decades, yet many key questions remain. In particular, the factors that control the temperature-dependent relaxation and viscous properties of the liquid phase as the glass transition is approached (that is, whether the glass-forming liquid is ‘fragile’ or ‘strong’5,6,7) remain unclear. Here we show that the fragility of a glass-forming liquid is intimately linked to a very basic property of the corresponding glass phase: the relative strength of shear and bulk moduli, or Poisson's ratio.
457 citations
TL;DR: The hydrogen bond in polymer blends is an interesting and important subject of research as its presence usually enhances the miscibility of the blend as discussed by the authors, and methods to incorporate interassociated hydrogen bonds into immiscible blends are reviewed, based on work over the last twenty or so years.
438 citations
TL;DR: In this article, high-strength Fe-based bulk glassy alloys with super-high fracture strength of over 4000 MPa and high glass-forming ability were synthesized by the copper mold casting method.
438 citations
TL;DR: In this article, the effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass-transition temperature (Tg) have been studied.
Abstract: With advances in nanoscience and nanotechnology, there is increasing interest in polymer nanocomposites, both in scientific research and for engineering applications. Because of the small size of nanoparticles, the polymer–filler interface property becomes a dominant factor in determining the macroscopic material properties of the nanocomposites. The glass-transition behaviors of several epoxy nanocomposites have been investigated with modulated differential scanning calorimetry. The effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass-transition temperature (Tg) have been studied. In comparison with their counterparts with micrometer-sized fillers, the nanocomposites show a Tg depression. For the determination of the reason for the Tg depression, the thermomechanical and dielectric relaxation processes of the silica nanocomposites have been investigated with dynamic mechanical analysis and dielectric analysis. The Tg depression is related to the enhanced polymer dynamics due to the extra free volume at the resin–filler interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3849–3858, 2004
337 citations
TL;DR: In this paper, the authors discuss the various methods used to obtain the model equations and illustrate the effects of structure on dynamics and scaling behavior over different time scales using a wave-vector-dependent model.
Abstract: Mode-coupling theory is an approach to the study of complex behavior in the supercooled liquids which developed from the idea of a nonlinear feedback mechanism. From the coupling of slowly decaying correlation functions the theory predicts the existence of a characteristic temperature ${T}_{c}$ above the experimental glass transition temperature ${T}_{g}$ for the liquid. This article discusses the various methods used to obtain the model equations and illustrates the effects of structure on dynamics and scaling behavior over different time scales using a wave-vector-dependent model. It compares the theoretical predictions, experimental observations, and computer simulation results, and also considers phenomenological extensions of mode-coupling theory. Numerical solutions of the model equations to study the dynamics from a nonperturbative approach are also reviewed. The review looks briefly at recent observations from landscape studies of model systems of structural glasses and their relation to the mode-coupling temperature ${T}_{c}$. The equations for the mean-field dynamics driven by the $p$-spin interaction Hamiltonian are similar to those of mode-coupling theory for structural glasses. Related developments in the nonequilibrium dynamics and generalization of the fluctuation-dissipation relation for the structural glasses are briefly touched upon. The review ends with a summary of the open questions and possible future direction of the field.
TL;DR: Intracellular glasses exhibit a high molecular packing and slow molecular mobility, resembling glasses made of mixtures of proteins and sugars, which potentially interact with additional cytoplasmic components such as salts, organic acids, and amino acids above the glass transition temperature.
TL;DR: In this article, a series of polymerizable ionic liquid was synthesized and polymerized to prepare new type polymer electrolytes, and the effects of position of imidazolium cation, spacer structure and length, and anion species on the ionic conductivity have been investigated.
TL;DR: In this article, the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA) nanocomposites was shown to drop by 25 °C when compared to the neat polymer.
Abstract: Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by an in situ free-radical polymerization process with 38 and 17 nm diameter γ-alumina nanoparticles. At extremely low filler weight fractions (<1.0 wt % of 38 nm fillers or < 0.5 wt % of 17 nm fillers) the glass-transition temperature (Tg) of the nanocomposites drops by 25 °C when compared to the neat polymer. Further additions of filler (up to 10 wt %) do not lead to additional Tg reductions. The thermal behavior is shown to vary with particle size, but this dependence can be normalized with respect to a specific surface area. The nanocomposite Tg phenomenon is hypothesized to be because of nonadhering nanoparticles that serve as templates for a porous system with many internal interfaces that break up the percolating structure of dynamically heterogeneous domains recently suggested by Long, D.; and Lequeux, F. Eur Phys J E 2001, 4, 371 to be responsible for the Tg reductions in polymer ultrathin films. The results also point to a far field effect of the nanoparticle surface on the bulk matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4371–4383, 2004
TL;DR: In this article, a sonication technique was used to disperse fluorinated single-wall carbon nanotubes (FSWCNT) in the glassy epoxy network resulting in nanocomposites having large improvement in modulus with extremely small amount of FSWCNT.
TL;DR: The experimental heat capacity of liquid PLA can be expressed by Cp(liquid)=(12017+0076T) J(lactic acid)−K−1−1··−mol−1 and has been compared to the ATHAS Data Bank, using contributions of other polymers with the same constituent groups.
TL;DR: Free films based on glucuronoxylan isolated from aspen wood were prepared by casting from aqueous solutions and drying in a controlled environment and thus examination of the material properties of these films found that films with xylitol gave lower extensibility.
TL;DR: Interestingly, WTC(g) and delta C(p) showed a negative linear correlation, indicating that the change in heat capacity during the glass transition is associated with the strength of the hydrogen-bonding network in the glassy state.
TL;DR: In this article, the brittle-to-ductile transition in uniaxial tension was found to depend on poor interfacial adhesion between polymer and nanoparticle, which allows the nucleation of voids, typically by larger particles.
Abstract: Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized using 38 and 17 nm alumina nanoparticles. At an optimum weight fraction, the resulting nanocomposites display a room-temperature brittle-to-ductile transition in uniaxial tension with an increase in the strain-to-failure that averages 40% strain and the appearance of a well-defined yield point in uniaxial tension. Concurrently, the glass transition temperature (Tg) of the nanocomposites drops by more than 20 °C. The brittle-to-ductile transition is found to depend on poor interfacial adhesion between polymer and nanoparticle. This allows the nucleation of voids, typically by larger particles (∼100 nm), which subsequently expand during loading. This void formation suppresses craze formation and promotes delocalized shear yielding. In addition, the reduction in Tg shrinks the shear yield envelope, further promoting this type of yield behavior. The brittle-to-ductile phenomenon is found to require both larger particles for void growth a...
TL;DR: In this paper, the phase behavior and the morphology in thin films of poly(3-hexylthiophene) (P3HT) have been studied using calorimetry, X-ray scattering, and scanning force microscopy (AFM).
Abstract: The thermodynamic phase behavior and the morphology in thin films of poly(3-hexylthiophene) (P3HT) has been studied using calorimetry, X-ray scattering, and scanning force microscopy (AFM). Around 225 °C a phase transition from the crystalline state to a layered, liquid crystalline structure occurs in regioregular P3HT, while the regiorandom counterpart material is disordered at all temperatures and displays a glass transition temperature T
g
≈−3 °C. Regioregular P3HT is semicrystalline and forms needle or plate like crystallites which in solution cast thin films are oriented with respect to the substrate. Films produced by spin coating display a non-equilibrium structure with reduced order and orientation. Annealing of these films in the liquid crystalline state leads to the formation of a morphology similar to the one observed in solution cast films.
TL;DR: Time-resolved optical Kerr effect measurements are reported that unambiguously demonstrate that the structural relaxation of liquid and weakly supercooled water follows the behaviour predicted by simple mode-coupling theory, supporting the interpretation of the singularity as a purely dynamical transition.
Abstract: Water has many kinetic and thermodynamic properties that exhibit an anomalous dependence on temperature, in particular in the supercooled phase. These anomalies have long been interpreted in terms of underlying structural causes, and their experimental characterization points to the existence of a singularity at a temperature of about 225 K. Further insights into the nature and origin of this singularity might be gained by completely characterizing the structural relaxation in supercooled water. But until now, such a characterization has only been realized in simulations that agree with the predictions of simple mode-coupling theory; unambiguous experimental support for this surprising conclusion is, however, not yet available. Here we report time-resolved optical Kerr effect measurements that unambiguously demonstrate that the structural relaxation of liquid and weakly supercooled water follows the behaviour predicted by simple mode-coupling theory. Our findings thus support the interpretation of the singularity as a purely dynamical transition. That is, the anomalous behaviour of weakly supercooled water can be explained using a fully dynamic model and without needing to invoke a thermodynamic origin. In this regard, water behaves like many other, normal molecular liquids that are fragile glass-formers.
TL;DR: In this article, the glass transition temperature (Tg) of chitosan (140 ∼ 150°C) was determined by means of four techniques, namely, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally simulated current spectroscopy (TSC), and dilatometry (DIL).
Abstract: Studies on the glass transition temperature (Tg) of chitosan are difficult to pursue because of the difficulty in sample preparation and the hydroscopicity of samples. There are a few works concerning this principal relaxation of chitosan. Among them, several quite different values (150°C, 161°C, and 203°C) have been reported. In this paper, the Tg of chitosan (140 ∼ 150°C) was determined by means of four techniques, namely, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally simulated current spectroscopy (TSC), and dilatometry (DIL).
DSC measurement has been assumed not to be sensitive enough to detect the relaxation temperature of polysaccharides. We propose a new method to improve the sensitivity of the DSC measurement. After a physical aging treatment of samples, the transition in DSC traces became much more distinct because of the enthalpy relaxation. This technique was also used to distinguish the Tg from other relaxations.
The Tg of chitosan with different degree of deacetylation (D.D.) was examined by DSC. No influence of D.D. on Tg was found. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1553–1558, 2004
TL;DR: The key features of these new salts are their low melting points or extremely low glass transition, and considerably low viscosities, which are compared with the reported [BF4](-)-based ones.
Abstract: A series of twenty two hydrophobic ionic liquids, 1-alkyl(alkyl ether)-3-methylimidazolium ([C(m)mim]+ or [C(m)O(n)mim]+; where Cm is 1-alkyl, Cm = nCmH(2m+1), m = 1-4 and 6; C(m)O(n) is 1-alkyl ether, C2O1 = CH3OCH2, C3O1 = CH3OCH2CH2, and C5O2 = CH3(OCH2CH2)2) perfluoroalkyltrifluoroborate ([RFBF3]-, RF = CF3, C2F5, nC3F7, nC4F9), have been prepared and characterized. Some of the important physicochemical properties of these salts including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and were compared with those of the reported [BF4](-)-based ones. The influence of the structure variation in the imidazolium cation and the perfluoroalkyltrifluoroborate ([RFBF3]-) anion on the above physicochemical properties was discussed. The key features of these new salts are their low melting points (-42 to 35 degrees C) or extremely low glass transition (between -87 and -117 degrees C) without melting, and considerably low viscosities (26-77 cP at 25 degrees C).
TL;DR: In this paper, it was observed that polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days.
Abstract: It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between Tg and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.
TL;DR: Detailed calorimetric characterizations of hyperquenched inorganic glasses that, when heated, do not crystallize before reaching their glass transition temperatures are reported, substantiating the conclusion that the glass transition of water cannot be probed directly.
Abstract: The formation of glasses is normal for substances that remain liquid over a wide temperature range (the ‘good glassformers’) and can be induced for most liquids if cooling is fast enough to bypass crystallization. During reheating but still below the melting point, good glassformers exhibit glass transitions as they abruptly transform into supercooled liquids, whereas other substances transform directly from the glassy to the crystalline state. Whether water exhibits a glass transition before crystallization has been much debated over five decades1,2,3,4,5,6. For the last 20 years, the existence of a glass transition at 136 K (ref. 3) has been widely accepted2,3,4, but the transition exhibits qualities difficult to reconcile with our current knowledge of glass transitions2,5,6. Here we report detailed calorimetric characterizations of hyperquenched inorganic glasses that, when heated, do not crystallize before reaching their glass transition temperatures. We compare our results to the behaviour of glassy water and find that small endothermic effects, such as the one attributed to the glass transition of water, are only a ‘shadow’ of the real glass transition occurring at higher temperatures, thus substantiating the conclusion6 that the glass transition of water cannot be probed directly.
TL;DR: In this paper, a large supercooled liquid region exceeding 40 K was obtained in the composition range of 30 to 70 at%Zr and 35 to 60 at%Hf.
Abstract: Glassy alloy rods with diameters up to 1.5 mm exhibiting a large supercooled liquid region before crystallization and high mechanical strength were formed in Cu-Zr and Cu-Hf binary alloy systems by the copper mold castingmethod. The large supercooled liquid region exceeding 40 K was obtained in the composition range of 30 to 70 at%Zr and 35 to 60 at%Hf. The largest value of the supercooled liquid region defined by the difference between glass transition temperature (Tg) and crystallization temperature (T x ), ΔT x (= T x - Tg), was 58 K for Cu 6 0 Zr 4 0 and 59 K for Cu 5 5 Hf 4 5 . The reduced glass transition temperature (T g /T 1 ) of the two alloys was 0.61 and 0.59, respectively. The alloys with large ΔT x above 50K were formed into a bulk glassy alloy form with diameters up to 1.5 mm by copper mold casting. The Cu 6 0 Zr 4 0 , Cu 4 5 Zr 5 5 , Cu 6 0 Hf 4 0 and Cu 5 5 Hf 4 5 glassy alloy rods exhibited high fracture strength of 1920, 1880, 2245 and 2260 MPa, respectively, Young's modulus of 107, 102, 120 and 121 GPa, respectively, a nearly constant elastic elongation of about 1.9% and plastic elongation up to 2.2%. The formation of these binary glassy alloy rods can he interpreted in the framework of the concept of the formation of the unique glassy structure consisting mainly of icosahedral atomic configuration as similar to that for special multi-component alloys with the three component rules.
TL;DR: The glassy alloy rods exhibit ultra-high fracture strength of 5185 MPa, high Young's modulus of 268 GPa and high specific strength of 6.5B31.
01 Jul 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the thermal properties, crystallization behavior, glass forming ability and mechanical properties of Ti-based amorphous alloys were studied by using differential scanning calorimetry (DSC), X-ray diffractometry, transmission electron microscopy and compressive test.
Abstract: The thermal property, crystallization behavior, glass forming ability (GFA) and mechanical properties of Ti-based amorphous alloys were studied by using differential scanning calorimetry (DSC), X-ray diffractometry, transmission electron microscopy and compressive test. These alloys were developed systematically by considering atomic size and interaction parameters between constituting elements. Partial replacement of Cu by Be and Ti by Zr in Ti–Cu–Ni–Sn alloy improved the GFA. Fully amorphous rods, of diameter 2, 5 and 8 mm, could be fabricated by injection casting Ti 50 Cu 25 Ni 15 Sn 3 Be 7 , Ti 45 Cu 25 Ni 15 Sn 3 Be 7 Zr 5 and Ti 40 Zr 25 Ni 8 Cu 9 Be 18 alloys, respectively. The T rg (= T g / T l ) and γ (= T x /( T g + T l )) parameter shows a relatively good agreement with the maximum diameter of bulk glass, while Δ T x has poor relationship with the GFA of alloys. The bulk amorphous alloys exhibit high compressive strength of approximately 2500 MPa with good ductility.
Abstract: Multi-walled carbon nanotubes (MW-CNTs) were dispersed throughout a thermosetting polyimide Triple A PI (TriA-PI). TriA-PI is a newly developed phenylethynyl terminated polyimide, and exhibits excellent mechanical properties and processability with high glass transition temperature (T g >300 °C ). The resulting composites containing 3.3, 7.7, 14.3 wt% MW-CNT exhibited relatively good dispersion in macroscopic scale. Tensile tests on the composites showed an increase in the elastic modulus and the yield strength, and decrease in the failure strain. Dynamic mechanical analysis (DMA) showed an increase in the glass transition temperature with incorporation of the carbon nanotubes. The experimental results suggested that the carbon nanotubes are acting as macroscopic crosslinks, and are further immobilizing the polyimide chains at elevated temperature.
TL;DR: In this paper, the effects of filler content and mixing time on the phase morphology, crystallization behavior, rheology, and mechanical properties of immiscible polypropylene(PP)/polystyrene(PS) blends compatibilized with nano-SiO 2 particles were investigated.