Width Of Glass Transition Research Articles

Glass transition kinetics and fragility of ZrCuAlNi(Nb) metallic glasses

The kinetics of glass transition and the fragility of Zr55Cu30Al10Ni5 and (Zr55Cu30Al10Ni5)98Nb2 metallic glasses were investigated by the calorimetric measurements. The Nb minor addition narrows the width of glass transition, accelerates the relaxation process during glass transition, and decreases the energy barrier of glass transition. In addition, the fragility was evaluated in terms of the kinetic fragility index. While both alloys can be classified as intermediate glass formers, the Nb minor addition remarkably decreases the fragility and a stronger glass is achieved by the microalloying process. The lower fragility in the Nb-containing alloy is accompanied by higher degree of short-range ordering inferred from structural characterizations, formation of nanoscale chemical heterogeneities evidenced from the energy-dispersive X-ray spectroscopy (EDS) results, and deteriorated plasticity evaluated from the bending experiments. Our results highlight positive correlations between the fragility and the plasticity of the studied glasses.

Topological Origin of the Super‐Flexible Phase of Se and Se‐Rich Glasses and Aging‐Induced 5‐fold Narrowing of Glass Transition Width

Pure Se glass and ternary AxBySe1−x−y glasses where A = Ge and B = P or As, in the low mean coordination number, ⟨r⟩, range of 2.00 < ⟨r⟩ < 2.12 display a 3‐ to 5‐fold reduction in the width of the glass transition when aged at room temperature over 4–8 months. Group IV (Ge) and group V (P, As) additives serve to crosslink the base Se glass polymeric chains, Sen, with n > 250 atoms and to reduce the length “n” between cross‐link points as x and y are increased. Herein, it is shown that in such weakly crosslinked glasses, the continued narrowing of the glass transition width Tg by a factor of 3–5, as in pure Se, stems from the fact that polymeric Sen chain segments between the crosslink points continue to have a length n of at least eight atoms or more. Such polymeric Sen chains are super‐flexible and reconstruct with each, as in pure Se, promoting structural ordering responsible for Tg narrowing. When n < 8, super flexibility is steadily lost. Along with the flexible, intermediate, and stressed‐rigid phases, a new super‐flexible phase of Se and Se‐rich glasses is obtained.

Relaxation dynamics in multicomponent glass formers with adjustable concentration fluctuations

Here, we study the structural relaxation kinetics in modified binary (i.e., ternary) mixtures with strong concentration fluctuation imposed by a polar picoline and an apolar triphenylethylene by adding a surfactant phenanthridine. The dielectric and enthalpy relaxation measurements are applied to monitor the dynamic properties aiming at distinguishing various effects of the concentration fluctuation. It is found that the strong concentration fluctuations are largely suppressed by adding the surfactant molecule. However, compared with the binary mixtures, a larger difference in the glass transition temperatures determined by the dielectric and enthalpy methods is observed in some of the ternary mixtures. Another unusual behavior in the ternary mixtures is that the enthalpy relaxation produces higher non-exponential factor β than the dielectric relaxation. The comparison of various parameters confirm that the reduced glass transition width is more suitable for characterizing the strength of concentration fluctuations in multi-component systems.

Dynamic coordination of miscible polymer blends towards highly designable shape memory effect

Miscible polymer blends offer great designability on shape memory effect (SME) with adjustable mechanical properties and stimuli-responsiveness, by simply changing the constituent compositions. However, the thermodynamics understanding behind those SMEs on miscible polymer blends are yet to be explored. This paper describes an approach to achieve highly designable SMEs with adjustable glass transition temperature (Tg) and width of glass transition zone by dynamically coordinating components in miscible blends. An extended domain size model was formulated based on the Adam-Gibbs theory and Gaussian distribution theory to study the synergistic coordination of component heterogeneities on conformational entropy, glass transition and relaxation behavior of the miscible blend. The effectiveness of model was demonstrated by applying it to predict dual- and triple-SMEs in miscible polymer blends, where the theoretical results show good agreements with the experiment results. We expect this study provide an effective guidance on designing advanced miscible polymer blends based on the SME.

Viscosity, relaxation and fragility of the Ca65Mg15Zn20 bulk metallic glass

The fragility of Ca65Mg15Zn20 bulk metallic glass was evaluated from calorimetric kinetics by differential scanning calorimeter and viscosity measurement. From the thermal analysis, the glass transition width was carefully determined to estimate the fragility, and the obtained fragility parameter D∗ is dependent on the pre-factor while the fragility index m keeps invariable, which indicates that m will be more reliable to display the fragility behavior. The viscosity in both the melt state and supercooled liquid region was measured and fitted using different equations as well. The fragility index m estimated from calorimetric method is smaller than that from viscosity in the supercooled liquid region which is ascribed to that the calorimetric evaluation of fragility corresponds to the glass state (non-equilibrium state) rather than supercooled liquid state (equilibrium state). The measured viscosity in the melt state is smaller than that predicted by VFT and Mauro equation when extrapolating the value from the supercooled liquid region to higher temperatures. This deviation implies that different regimes of dynamic behavior exists in the two states, and a dynamic crossover of viscosity may occur at the critical temperature Tc as suggested by the mode coupling theory.

Effect of bimodal molecular weight distribution on glass transition of confined polystyrene

We study the effect of bimodal molecular weight distribution on glass transition of polystyrene (PS) under one-dimensional confinement by employing hot-stage spectroscopic ellipsometry. The bulk PS is found to have an exceptionally low glass transition temperature (Tg) of around 61 °C. This intriguing finding is attributed to the presence of a sizable fraction of very low molecular weight components (∼3000 g/mol). A further suppression of Tg compared to the already reduced bulk value is observed upon reduction of the film thickness. We also observe that glass transition width of the bulk PS is broader than its monodisperse counterpart which is further broadened upon confinement.

Thermal Properties and Conductivity of Thermally Treated Epoxidized Natural Rubber‐Based Solid Polymer Electrolytes

Thermal properties and ionic conductivity of epoxidized natural rubber (ENR)‐based solid polymer electrolytes (SPEs) are influenced by their sample preparatory pathways. In literature, there are inconsistencies reported on conductivity values in the range of 10−8–10−9 S cm−1 due to different sample preparatory pathways for same systems at constant salt concentration. In this study, simple thermal treatment was adopted on SPE films for regulating the thermal properties of the materials which in turn to govern the conductivity of the materials. ENR (with 25 and 50 mol% epoxidation) and lithium perchlorate salt (0–20 wt.%) were used. The ENR‐based SPE films were thermally treated with three different annealing times (i.e. t = 0, ½, 24 h) at 80 °C under nitrogen atmosphere. Differential scanning calorimetry and impedance spectroscopy were utilized to analyze the thermal properties and ionic conductivity at room temperature, respectively. The glass transition parameters such as glass transition temperature, change in heat capacity, width of glass transition and change in enthalpy of endothermic overshoot were elucidated. Higher glass transition temperature values are noted for ENR‐based SPEs films with longer annealing time, which may imply higher extent of intermolecular interaction between ENR and salt, thus leading to an increase in ionic conductivity of ∼10−10–10−8 S cm−1 for t = 0 and 24 h, respectively at mass fraction of salt, WS = 0.107. Consequently, it is deemed important to have precise control in the thermal treatment of ENR‐based SPEs during their preparatory stage.

Molecular origin of aging of pure Se glass: Growth of inter-chain structural correlations, network compaction, and partial ordering.

Glass transition width W of pure Se narrows from 7.1(3) °C to 1.5(2) °C and the non-reversing enthalpy of relaxation (ΔHnr) at Tg increases from 0.23(5) cal/g to 0.90(5) cal/g upon room temperature aging for 4 months in the dark as examined in modulated differential scanning colorimetry (MDSC) at low scan rates. In Raman scattering, such aging leads the A1 mode of Sen-chains (near 250 cm-1) to narrow by 26% and its scattering strength to decrease as the strength of modes of correlated chains (near 235 cm-1) and of Se8 rings (near 264 cm-1) systematically grows. These calorimetric and Raman scattering results are consistent with the "molecular" chains of Sen, predominant in the fresh glass, reconstructing with each other to compact and partially order the network. Consequences of the aging induced reconstruction of the long super-flexible and uncorrelated Sen-chains are also manifested upon alloying up to 4 mol. % of Ge as revealed by a qualitative narrowing (by 25%) of the Raman vibrational mode of the corner-sharing GeSe4 tetrahedra and a blue-shift of the said mode by nearly 1 cm-1 in 194 cm-1. But, at higher Ge content (x> 6%), as the length of Sen chain-segments across Ge cross-links decreases qualitatively (⟨n⟩ < 8), these aging induced chain-reconstruction effects are suppressed. The width of Tg increases beyond 15 °C in binary GexSe100-x glasses as x> 10% to acquire values observed earlier as alloying concentration approaches 20% and networks become spontaneously rigid.

Mixed alkali silicophosphate oxynitride glasses: Structure-property relations

We investigate the structure, molar volume, dynamic behavior at the glass transition, and micromechanical properties of mixed Li2O-Na2O silicophosphate oxynitride glasses with varying R2O/SiO2 and N/O ratios. The degree of nitrogen-for-oxygen substitution along with the resulting PO4−yNy local bonding configurations is analyzed. Changes in the short (SRO) and intermediate range order (IRO) structures are determined through Raman spectroscopy, 31P and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). In the silica-free oxynitride phosphate glasses, the property changes with N/P ratio are associated with structural changes induced by N atoms. In the silicophosphate oxynitride glasses, structural changes are caused by both nitrogen and SiO2. For high silica content compositions, nitridation has only a minor effect on the measured properties, even for the sample with highest N/P ratio. Differential scanning calorimetry (DSC) measurements show that nitrogen incorporation into the silicophosphate glass network increases the glass transition temperature (Tg) and width of the glass transition (ΔTg), but the magnitude of these changes depend strongly on the silica content. On the other hand, the jump in isobaric heat capacity at the glass transition (ΔCp) and the liquid fragility index (m) do not exhibit systematic dependence on the N content. We discuss the glassy dynamics in terms of the distribution of nitride and silicon species within the phosphate sub-network. The changes in the IRO structural motifs upon SiO2 addition are explained by considering both the formation of the six-fold coordinated Si species in the silicate sub-network and the fact that Q3(P) shares only two bridging oxygen with P atoms, as the third is shared with a Si atom.

Effect of Compression on the Molecular Arrangement of Itraconazole-Soluplus Solid Dispersions: Induction of Liquid Crystals or Exacerbation of Phase Separation?

Predensification and compression are unit operations imperative to the manufacture of tablets and capsules. Such stress-inducing steps can cause destabilization of solid dispersions which can alter their molecular arrangement and ultimately affect dissolution rate and bioavailability. In this study, itraconazole-Soluplus solid dispersions with 50% (w/w) drug loading prepared by hot-melt extrusion (HME) were investigated. Compression was performed at both pharmaceutically relevant and extreme compression pressures and dwell times. The starting materials, powder, and compressed solid dispersions were analyzed using modulated differential scanning calorimetry (MDSC), X-ray diffraction (XRD), small- and wide-angle X-ray scattering (SWAXS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and broadband dielectric spectroscopy (BDS). MDSC analysis revealed that compression promotes phase separation of solid dispersions as indicated by an increase in glass transition width, occurrence of a peak in the nonreversing heat flow signal, and an increase in the net heat of fusion indicating crystallinity in the systems. SWAXS analysis ruled out the presence of mesophases. BDS measurements elucidated an increase in the Soluplus-rich regions of the solid dispersion upon compression. FTIR indicated changes in the spatiotemporal architecture of the solid dispersions mediated via disruption in hydrogen bonding and ultimately altered dynamics. These changes can have significant consequences on the final stability and performance of the solid dispersions.

Impact of nitridation of metaphosphate glasses on liquid fragility

Oxynitride glasses are mixed-anion glasses, in which the oxygen atoms have been partially substituted by either two-fold (Nd) or three-fold (Nt) coordinated nitrogen atoms, introducing additional bonds and thereby constraining the glass network and enhancing the atomic packing density. Phosphate glasses are more prone to undergo nitridation via ammonolysis at relatively low temperature compared to other types of oxide glasses, but here the question is how the nitridation influences the glass transition, structure, and dynamics in phosphate glasses. Here, we answer this question by taking sodium and lithium metaphosphate oxynitride glasses as model systems. Using differential scanning calorimetry (DSC), we measure the effect of the atomic nitrogen/phosphorus (N/P) ratio on the glass transition temperature (Tg), jump in isobaric heat capacity at the glass transition (ΔCp), glass transition width (ΔTg), and liquid fragility index (m) of these model glasses. The results show that the nitridation causes an increase in the atomic packing density and Tg. In addition, ΔTg increases and m decreases with increasing N/P, both implying that the liquids become stronger upon nitridation, whereas ΔCp does not vary systematically with N/P within the error range. We discuss the origin of these changes in terms of the underlying changes in the short- and intermediate-range order structures, as detected by Raman spectroscopy.

Dependence of calorimetric glass transition profiles on relaxation dynamics in non-polymeric glass formers

The dependence between the calorimetric glass transition width ΔTg defined in heat capacity curves and structural relaxation dynamics is studied in analytical and experimental fashions. The Tool–Narayanaswamy–Moynihan–Hodge model is analyzed to extract the relations between the normalized glass transition width ΔTg/Tg and three dynamic parameters: fragility (m), stretching exponent (βKWW) and non-linear factor (x). When the other two dynamic parameters are fixed, ΔTg/Tg is found to scale linearly with 1/m or 1/βKWW, but not to show marked variation with x in the range of practically accessible values. Experimental data of more than 50 glass formers covering molecular, metallic and oxide systems are examined, and the linear relations are reproduced for m (or βKWW) among the chemicals of comparable βKWW (or m). Joint consideration of m and βKWW makes an empirical equation of ΔTg/Tg=2.20*(1/m+0.0026)*(1/βKWW−0.59) with high accuracy for all the materials. For the glass formers with similar βKWW, Moynihan's relation can be approximately restored.

Drug–Polymer Miscibility across a Spray Dryer: A Case Study of Naproxen and Miconazole Solid Dispersions

The structural and physical stability of solid dispersions have not been adequately explored during spray drying manufacturing processes. In this study a wide range of compositions of naproxen/PVP-VA 64 (poly(1-vinylpyrrolidone-co-vinyl acetate)) and miconazole/PVP-VA 64 solid dispersions prepared by different laboratory spray dryers were collected from various selected locations and used to investigate the drug-polymer mixing across spray dryers. Spray-dried dispersions with 30% (w/w) naproxen collected from the transport tube of the Pro-C-epT Microspray dryer showed the narrowest glass transition width, which apparently indicates the highest degree of drug-polymer mixing compared to the other locations. The intensity of the naproxen-PVP-VA 64 interaction peak at 1654 cm(-1) of IR spectra differs for solid dispersions (SDs) from the collector and transport tube of Pro-C-epT Microspray dryer with a higher intensity for the latter. Samples with 50% (w/w) naproxen loading collected from the cyclone and the cyclone steel part of the Buchi mini spray dryer showed a melting endotherm (Tm at 112.2 ± 0.8 °C and ΔHf between 0.7 and 1.8 J/g), whereas samples from the cyclone tube to the drying chamber were devoid of crystalline material. The variations in drug-polymer mixing extend to miconazole/PVP-VA solid dispersions where 20% drug loading showed location-dependent drug-polymer mixing. This study clearly showed that the variation in drug-polymer miscibility and solid form of the drug in solid dispersions can occur across spray dryer in small-scale manufacturing processes. The optimization of formulation parameters and spray drying process parameters is imperative to diminish these variations to enhance homogeneity of solid dispersions in laboratory scale spray dryers. The same problem can occur in geometrically large spray drying manufacturing equipment, and the robustness of the processes should be carefully assessed.

Glass transition, fragility, and structural features of amorphous nickel–tellurate–vanadate samples

The experimental FTIR spectra and DSC curves of the ternary 40TeO2–(60−x)V2O5–xNiO glasses with 0 ≤ x ≤ 30 (in mol%) have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (Tg), glass transition width (ΔTg), heat capacity change at glass transition (ΔCP) and Fragility (F). Thermal stability, fragility, and glass-forming tendency of these glasses have been estimated. Also, Poisson’s ratio (μ) and IR spectra of the presented systems have been investigated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus, and shear modulus, indicating a strong relation between elastic properties and structure of glass. In general, results of this work show that glasses with x = 0 and 30 have the highest shear and young’s modulus which make them as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 30 has higher handling temperature and super resistance against thermal shock.

Influence of molecular weight on enthalpy relaxation and fragility of amorphous carbohydrates

► The glass transition temperature increased with increasing molecular weight. ► Mean enthalpy relaxation time increased with increasing molecular weight. ► The KWW equation was able to describe enthalpy relaxation behavior of selected carbohydrates. ► Fragility analysis indicated maltose and maltotriose as strong systems. Enthalpy relaxation and fragility of selected carbohydrates were correlated with their molecular weight. Anhydrous glucose and its oligomers (i.e. maltose and maltotriose) were selected to represent amorphous carbohydrates with increasing molecular weight. The enthalpy relaxation behavior of glucose, maltose and maltotriose was determined at 5 °C below their respective glass transition temperatures using differential scanning calorimetry (DSC). The non-exponential behavior of enthalpy relaxation was fitted with the Kohlrausch–Williams–Watts (KWW) equation. The mean relaxation time constants ( τ ) for glucose, maltose and maltotriose at ( T g − 5) were 16.9, 38.4 and 128.6 h, respectively. The fragility indices ( m ) of glucose, maltose and maltotriose, determined using the DSC glass transition width approach, were 105, 88.1 and 97.6, respectively. The glass transition temperature and mean enthalpy relaxation time increased with increasing molecular weight for the selected carbohydrates studied herein. The greater glass transition temperature and enthalpy relaxation time of maltotriose are attributed to the decreased specific volume, segmental mobility and increased entanglements resulting from its higher molecular weight. Maltotriose may be preferred as an encapsulant or food ingredient to reduce structural relaxation in food formulations during storage.

DSC and elastic moduli studies on tellurite-vanadate glasses containing antimony oxide

xSb2O3-40TeO2-(60 − x) V2O5 glasses with 0 ≤ x ≤ 10 (in mol%) have been prepared by rapid- melt quenching method. DSC curves of these ternary glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (Tg), glass transition width (ΔTg), heat capacity change at glass transition (ΔCP) and fragility (F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been estimated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 0 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 8 has higher handling temperature and super resistance against thermal attack.

Optical, thermal and electrical properties of ternary TeO2–WO3–PbO glasses

Abstract Optical absorption, MDSC and DC conductivity studies have been used to study the influence of WO3 and PbO oxides on optical, thermal and conductivity properties of the TeO2–WO3–PbO glass system. From MDSC thermogram, the glass transition temperature (Tg), onset crystallization (To), thermal stability (ΔT), glass transition width (ΔTg), heat capacities in the glassy and liquid state (Cpg and Cpl), heat capacity change (ΔCp) and ratios Cpl/Cpg of the glass systems were calculated. The variation in Tg with the addition of PbO content has been correlated with structural properties ( n c ¯ , nb, F ¯ ). The optical band gap (Eopt), Urbach energy (ΔE), molar refraction (RM), metallization criterion (M), optical basicity (Λ), electronic polarizability of the oxide ion ( α O 2 - ) and refractive index (n) have been determined from optical absorption data and their variations have been discussed in terms of the glass structure. DC electrical conductivity of the present glasses was studied in the temperature range of 150 °C to below their Tg values. The activation energies (Eact) of all the glasses for the conduction were calculated and found to be composition dependent.

Fragility, DSC and elastic moduli studies on tellurite–vanadate glasses containing molybdenum

Ternary xMoO 3–40TeO 2–(60 − x)V 2O 5 glasses with 0 ⩽ x ⩽ 60 (in mol%) have been prepared by normal melt quenching method. DSC curves of these glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature ( T g ), glass transition width (Δ T g ), heat capacity change at glass transition (Δ C P) and calculated fragility ( F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been evaluated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for calculation of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 60 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 20 has higher handling temperature and super resistance against thermal attack.

Raman and DSC studies of fragility in tellurium‐zinc oxide glass formers

AbstractRaman scattering and differential scanning calorimetry (DSC) measurements have been carried out in four mixed (TeO2)1‐x(ZnO)x (x = 0.1, 0.2, 0.3, 0.4) glasses at high temperatures (Raman and DSC through the glass transition) and high pressures (Raman) with the aim of determining the fragility of these glass forming oxides. Four different criteria, corresponding to four parameters, were applied to assess the fragility of the glasses. From the DSC studies, we have obtained the fragility parameter m which corresponds to the slopes of Arrhenius (lnQ vs. 1/Tg, were Q is the heating rate) plots, and the glass transition width ΔTg. Also, from the low‐frequency Raman scattering, and in particular the boson peak intensity of the glasses at Tg, we have estimated the fragility ratio rR (Tg) = Imin/Imax whose value serves as another (empirical) fragility criterion. Finally, from high pressure Raman measurements on the glasses, we have estimated the Grüneisen parameter γT for each glass, which constitutes the fourth fragility parameter adopted in this work. Considering the four parameters ΔTg, m, r (Tg) and γT and the generally accepted (empirical) fragility criteria, we conclude that the mixed tellurium‐zinc oxides constitute strong‐to‐intermediate glass formers (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Interactions in a blend of two polymers greatly differing in glass transition temperature

Blends of poly(N-methyldodecano-12-lactam) PMDL with poly(4-vinyphenol) PVPh have been studied by the DSC and ATR FTIR methods. The difference in glass transition temperature Tg between the components is 206 °C. A single composition-dependent Tg suggests miscibility of the system, that is, homogeneity on the scale of about 10 nm. Fitting of the equation of Brostow et al. to the Tg data indicates relatively strong specific interactions and high complexity of the system. The Schneider's equation applied separately to low- and high-PVPh regions provides good agreement with experiment; the calculated curves cross at the point of PVPh weight fraction 0.27. In the low-PVPh region, the analysis indicates weak interactions with predominance of segment homocontacts and strong involvement of conformational entropy. In the high-PVPh region, strong specific interactions predominate and entropic effects are suppressed. Composition dependences of the heat capacity difference at Tg and the width of glass transition indicate strong interactions in the system and existence of certain heterogeneities on segmental level, respectively. According to ATR FTIR, hydrogen bonds between PVPh as proton donor and PMDL as proton acceptor induce miscibility in blends of higher PVPh content (above about 0.28 weight fraction). In low-PVPh blends, it is conformational entropy that enables intimate intermolecular mixing. Hydrogen bonds adopt several (distorted) geometries and are on average stronger than average hydrogen bonds formed in self-associating PVPh. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011