Glass Transition Phenomenon Research Articles

Understanding Glass through Differential Scanning Calorimetry.

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.

Glass Transition Phenomenon for Conjugated Polymers

AbstractConjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin‐like electronics, wearable optoelectronics, and sensory technologies. In the past three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their thermomechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, have received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semirigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long‐term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories, and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a few empirical design rules are proposed to fine‐tune the glass transition temperature for conjugated polymers. The review paper is finished with perspectives on future directions on studying the glass transition phenomena of conjugated polymers. The goal of this perspective is to draw attention to challenges and opportunities of controlling, predicting, and designing polymeric semiconductors, specifically to accommodate their end use.

Thermo-kinetic behaviour of Ge20Te75I5 glass for infrared optics

ABSTRACTThe iodine-doped GeTe4 infrared chalcogenide glass was studied by means of differential scanning calorimetry DSC, X-ray diffraction XRD, Raman spectroscopy and infrared microscopy. Extensive non-isothermal thermo-kinetic characterisation of the glass transition, crystallisation and melting phenomena was performed in dependence on the particle size. The Tool–Narayanaswamy–Moynihan model was applied to describe the enthalpy relaxation processes: the compositional evolution of the relaxation parameters was then explained in terms of the structural changes and movements of the characteristic structural units. Mathematic deconvolution was applied to treat the complex crystallization kinetics – two crystal growth sub-processes were identified and described in terms of the autocatalytic Šesták-Berggren model. Based on the XRD and microscopic analyses the following crystallization mechanisms were revealed: initial precipitation of tellurium (surface-located) followed by a combined surface- and bulk-located formation of GeTe and GeI4 phases. Based on the DSC results obtained for fine powders, the presence of mechanically induced defects was found to accelerate the Te precipitation, the consequences of which are discussed with regard to the performance of nowadays glass stability criteria.

Thermal & Dielectric Spectroscopic Investigation on Orientationaly Disordered Crystal- Cyclobutanol

Abstract Orientationallydisordered crystals (plastic crystals) maintain translational order along their crystallographic axis while continue to have orientational degrees of freedom. Since freezing of orientational motion of molecule leads to glass transition, these rotationally disordered systems form glassy crystals below their glass transition temperature. Because of the presence of translational order, these kind of materials can easily treated in both mathematical and simulation approaches and are considered as the ideal or model system for studying glass transition phenomena. Here by using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), thermal and dielectric behaviour of the orientation ally disordered phases of an organic plastic crystal cyclobutanol have been studied. During quench cooling of the sample below the melting point, three solid-solid phase transitions, one at 180K called phase I, other at 170K called phase II, and another one at 158 K and glass transition (133K) events were observed using the DSC. The dielectric spectra of the cyclobutanol were recorded in a wide frequency range of 10-2 Hz to 107Hz for different temperatures. The dielectric spectra revealed the presence of the three phases, of which phase I was observed below the melting point up to nearly 180 K, the phase II was observed up to nearly 170 K and phase III was observed further up to 158K. In these phases signatures of two structural α relaxations were observed. The secondary relaxation below the glass transition event was also seen, whose strength was found to be very small compared to those observed in other plastic crystals. The α relaxation showed non-Arrhenius temperature dependence depicted by Vogel-Fulcher-Tammann equation,while secondary relaxation mimicked Arrhenius temperature dependence.

Cu nanoparticles constrain segmental dynamics of cross-linked polyethers: a trade-off between non-fouling and antibacterial properties.

Copper has a strong bactericidal effect against multi-drug resistant pathogens and polyethers are known for their resistance to biofilm formation. Herein, we combined Cu nanoparticles (NPs) and a polyether plasma polymer in the form of nanocomposite thin films and studied whether both effects can be coupled. Cu NPs were produced by magnetron sputtering via the aggregation in a cool buffer gas whereas polyether layers were synthesized by Plasma-Assisted Vapor Phase Deposition with poly(ethylene oxide) (PEO) used as a precursor. In situ specific heat spectroscopy and XPS analysis revealed the formation of a modified polymer layer around the NPs which propagates on the scale of a few nanometers from the Cu NP/polymer interface and then transforms into a bulk polymer phase. The chemical composition of the modified layer is found to be ether-deficient due to the catalytic influence of copper whereas the bulk polymer phase exhibits the chemical composition close to the original PEO. Two cooperative glass transition phenomena are revealed that belong to the modified polymer layer and the bulk phase. The former is characterized by constrained mobility of polymer segments which manifests itself via a 30 K increase of dynamic glass transition temperature. Furthermore, the modified layer is characterized by the heterogeneous structure which results in higher fragility of this layer as compared to the bulk phase. The Cu NPs/polyether thin films exhibit reduced protein adsorption; however, the constrained segmental dynamics leads to the deterioration of the non-fouling properties for ultra-thin polyether coatings. The films are found to have a bactericidal effect against multi-drug resistant Gram-positive Methicillin-Resistant Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa.

Instability of common beans during storage causes hardening: The role of glass transition phenomena

Long-term storage of common beans leads to loss of cooking quality and an ill-defined solution, appropriate storage, is recommended. Therefore, the polymer science theory of glasses that hypothesizes stability of a system below its glass transition temperature (Tg) was applied to determine bean stability during storage in relation to cooking behavior. Since composition influences Tg, powders of cotyledons and seed coats in addition to whole beans were equilibrated above different saturated salt solutions in order to generate materials with different moisture contents. A thermal mechanical compression test which measures compressibility changes in a system upon reaching its glass-rubber transition temperature region was conducted to obtain the Tg. A Tg-moisture relation was established, whose relevance was confirmed by storage and cooking experiments which showed development of hard-to-cook in beans stored above Tg but not below it. Therefore, this relation constitutes a stability map for storage of common beans.

Stress Relaxation in Cylindrical Glass-To-Metal Junctions With Account for the Quality of a Junction Region

With account for a complex behavior of glass (the phenomenon of glass transition) and the degree of adhesion between glass and metal layers, a numerical-analytical method for calculating the evolution of a stress state of glass–metal composite during temperature treatment is proposed. The effect of relaxation processes in the glass–metal junction region on the technological and residual stresses in the composite is studied.

The comprehensive approach towards study of (azo)polymers fragility parameter: Effect of architecture, intra- and intermolecular interactions and backbone conformation

The comprehensive investigations including the influence of architecture, intra– and intermolecular interactions and backbone conformation on the glass transition activation energy and the temperature dependence of segmental relaxation (fragility) in a series (azo)polyimides are presented. The studies were carried out using DSC measurements. To understand the microscopic parameters that control the glass transition phenomenon the activation energy was calculated using two different approaches, i.e., Kissinger and Moynihan models. The behavior of polyimides near the glass transition was investigated in the context of formation intra- and intermolecular H-bonds, which impact on rigidity and conformation of main and side chains of the polymers. Presence of the H-bonds was confirmed experimentally by 1H NMR and FTIR spectroscopes and theoretically by DFT simulations. Our investigations showed, that the presence of intra- and intermolecular interactions cause different conformations of the polymer chain, what may be the key to solve the puzzle of fragility parameter of polymers.

Structural and EPR studies of Cu2+ ions in NaPO3 – Sb2O3 – CuO glasses

In this work, glass compositions in the system NaPO3 - Sb2O3 – CuO (PSbCu) containing different concentrations of CuO and Sb2O3 were prepared through the melt - quenching methodology. Thermal, structural and optical properties of the PSbCu glasses were systematically studied by differential scanning calorimetry (DSC), X – ray powder diffraction (XRD) and Raman, UV–Visible and Photoluminescence (PL) spectroscopies, besides electron paramagnetic resonance (EPR) measurements. The DSC curves for all samples presented the glass transition phenomenon (Tg), while the XRD patterns showed the presence of an amorphous halo, which confirmed the glassy nature of all samples analyzed. UV–Vis spectra of the glasses showed a transparent window from 450 to 800 nm. The EPR signals intensities were investigated as a function of the copper concentration and Sb2O3 content in the (PySb0.5Cu) (20 ≤ y ≤ 80) and (PSb80xCu) (0.25 ≤ x ≤ 1.25) glasses. The EPR results showed that the increase of Sb2O3 concentration on the PySb0.5Cu glasses decreased the Cu2+ signals, which suggests the Sb3+ oxidizing to Sb5+, also transferring electrons to Cu2+ species to create the EPR a silent Cu+ specie. According to EPR parameters and PL spectra (excited at 380 nm) of PySb0.5Cu glasses, the ions Cu2+ ions were preferentially found in a distorted octahedral geometry, while Cu+ is in a square planar geometry according to the Jahn-Teller effect.

Identification of complex glass transition phenomena by DSC in expanded cereal-based food extrudates: Impact of plasticization by water and sucrose

The physical state and mechanical properties of extruded cereal based products were studied as a function of sucrose content and relative humidity (RH) to evaluate how the presence of sucrose affects glass transition temperature (Tg), sorption isotherm, and texture parameters. Extrudates were prepared with different sucrose content (0–20 %wt). Sorption isotherm showed the water content of extrudates decreased when product contains high sucrose at low aw range and the inverse effect was observed at high aw. Tg s were determined using differential scanning calorimetry (DSC) and two transitions were detected on the heat flow first derivative curve. Addition of sucrose or water decreased both Tg s in extrudates. Young's modulus showed water acts as anti-plasticizer at low aw, while shows plasticizing effect at high aw. A stability map can explain the brittle-ductile transition occurred while it was below Tg.

Glass-ceramics from a zinc-electroplating solid waste: Devitrification promoted further crystallization of parent glass upon heat treatment

A solid waste from a zinc electroplating production line was successfully used as a main raw material for synthesizing glass-ceramics with a fine microstructure. X-ray fluorescence spectroscopy analysis on dried solid waste shows that the waste mainly contains iron and zinc oxides. X-ray diffraction (XRD) analysis identifies Fe3O4 and ZnO phases in calcined waste samples. Based on the above results, silica sand, lime stone and potassium feldspar were proportionally added to make parent glasses by melting the batches at 1450 °C for 2 h. The as-synthesized products show typical DSC and thermal expansion curves with obvious glass transition phenomenon. However, XRD patterns reveal that they had devitrified to form ZnFe2O4 phase during the shaping and cooling of the melts. The devitrification became weaker when more potassium feldspar was added. It is interesting to find that the pre-crystallization of ZnFe2O4 in the devitrified sample was beneficial to its further crystallization during the following heat-treatment. The result implies that the devitrification of parent glasses is not necessarily a detriment to the preparation of glass-ceramics via controlled crystallization process.

Viscoelasticity of Cu- and La-based bulk metallic glasses: Interpretation based on the quasi-point defects theory

The dynamic mechanical relaxation of metallic glasses is closely associated with the physical and mechanical properties. In the current work, the dynamic mechanical relaxation behaviors of Cu46Zr45Al7Y2 and La65Al14(Cu5/6Ag1/6)11(Ni1/2Co1/2)10 bulk metallic glasses are investigated by mechanical spectroscopy. In general, metallic glasses display two relaxation modes: main (α) relaxation and the slow secondary (β) relaxation. The α relaxation is linked to the dynamic glass transition phenomenon and viscous flow while the slow β relaxation is associated with many fundamental issues, such as diffusion and glass transition phenomenon. The experimental study shows La65Al14(Cu5/6Ag1/6)11(Ni1/2Co1/2)10 bulk metallic glass displays a noticeable slow β relaxation. Contrarily, the Cu46Zr45Al7Y2 bulk metallic glass relaxation process takes the form of an “excess wing”. In the framework of quasi-point defects (QPD) theory, the dynamic mechanical response of the metallic glasses is discussed.

Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x = 0–17.5 at%) glassy alloys

The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5–17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6%Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid.

Thermal analysis of cadmium addition on the glass transition and crystallization kinetics of Se–Te–Sn glassy network

Calorimetric measurements have been performed in quaternary glassy system Se78−xTe20Sn2Cdx (x = 0, 2, 4, and 6) to study the thermally induced glass transition and crystallization phenomena. The characteristics kinetic temperatures (glass transition temperature $$T_{\text{g}}$$ , onset crystallization temperature $$T_{\text{o}}$$ , peak crystallization temperature $$T_{\text{c}}$$ ) and static melting temperature $$T_{\text{m}}$$ of the quaternary glassy series have been determined using their non-isothermal DSC curves. These temperatures were utilized to calculate the thermal stability $$S$$ and the Hruby parameter $$H_{\text{R}}$$ for the studied glasses. Both the activation energy of glass transition $$E_{\text{t}}$$ and the activation energy of crystallization $$E_{\text{c}}$$ for all compositions were evaluated using the well-known Kissinger's relation and the method of Augis–Bennett. Values of the fragility index $$m$$ and the crystallization rate factor $$K_{\text{p}}$$ were estimated using the activation energy values $$E_{\text{t}}$$ and $$E_{\text{c}}$$ , respectively. The compositional dependence of the above-mentioned parameters was discussed on the basis of rigidity models and according to the formation of iono-covalent bonds when our glassy Se–Te–Sn system is doped with a heavy element as Cd.

Decoupling of Dynamic and Thermal Glass Transition in Thin Films of a PVME/PS Blend.

The discussions on the nanoconfinement effect on the glass transition and glassy dynamics phenomena have yielded many open questions. Here, the thickness dependence of the thermal glass transition temperature Tgtherm of thin films of a PVME/PS blend is investigated by ellipsometry. Its thickness dependence was compared to that of the dynamic glass transition (measured by specific heat spectroscopy) and the deduced Vogel temperature (T0). While Tgtherm and T0 showed a monotonous increase, with decreasing film thickness, the dynamic glass transition temperature (Tgdyn) measured at a finite frequency showed a nonmonotonous dependence that peaks at 30 nm. This was discussed by assuming different cooperativity length scales at these temperatures, which have different sensitivities to composition and thickness. This nonmonotonous thickness dependence of Tgdyn disappears for frequencies characteristic for T0. Further analysis of the fragility parameter showed a change in the glassy dynamics from strong to fragile, with decreasing film thickness.

Molecular Dynamics Study of Polystyrene-b-poly(ethylene oxide) Asymmetric Diblock Copolymer Systems.

Two polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers differing in molecular mass (49 and 78 kDa) but possessing the same PEO cylindrical morphology are examined to elucidate their molecular dynamics. Of particular interest here is the molecular motion of the PEO blocks involved in the rigid amorphous fraction (RAF). An analysis of complementary thermal calorimetry and X-ray scattering data confirms the presence of microphase-separated morphology as well as semicrystalline structure in each copolymer. Molecular motion within the copolymer systems is monitored by dielectric and nuclear magnetic resonance spectroscopies. The results reported herein reveal the existence of two local Arrhenius-type processes attributed to the noncooperative local motion of PEO segments involved in fully amorphous and rigid amorphous PEO microphases. In both systems, two structural relaxations governed by glass-transition phenomena are identified and assigned to cooperative segmental motion in the fully amorphous phase (the α process) and the RAF (the αc process). We measure the temperature dependence of the dynamics associated with all of the processes mentioned above and propose that these local processes are associated with corresponding cooperative segmental motion in both copolymer systems. In marked contrast to the thermal activation of the α process as discerned in both copolymers, the αc process appears to be a sensitive probe of the copolymer nanostructure. That is, the copolymer with shorter PEO blocks exhibits more highly restricted cooperative dynamics of PEO segments in the RAF, which can be explained in terms of the greater constraint imposed by the glassy PS matrix on the PEO blocks comprising smaller cylindrical microdomains.

Influence of synthesis conditions on thermal release of palm oil as liquid core filled in polymeric nanoparticles

After synthesis of poly(styrene-co-maleimide) nanoparticles with 70 mass% encapsulated palm oil, by an imidization reaction of the poly(styrene-co-maleic anhydride) copolymer with different concentrations of ammonium hydroxide, the thermal release properties of palm oil were studied under various temperatures and heating times. The altered reaction conditions lead to progressively higher imide contents, resulting in better thermal stability and retarded release profiles. Based on differential scanning calorimetry, the release of oil is associated with an exotherm reaction, while the glass transition phenomena may be partially masked due to the complex structure of the oil and organic phase. The isothermal scans show different rates of oil release followed by a post-imidization reaction. From dynamic mechanical analysis, the thermal release can be followed by changes in visco-elastic properties and a shift in maximum loss factor. The thermal release profiles after heating for 2 min to 6 h at 125–250 °C were identified from FTIR to Raman spectroscopy, following variations in oil-related and imide-related absorption bands. The amount of exposed oil progressively decreases at higher ammonium hydroxide concentrations, while the oil release is stabilized at temperatures below the glass transition temperature and linear oil release starts at temperatures above the glass transition temperature. The kinetics and mechanism of oil release can be described by the release rate and diffusion exponent of the Korsmeyer–Peppas model. Therefore, it was concluded that the diffusion mechanisms are closely related to the softening properties of the polymer, with linear time-dependent release (Fick diffusion) or more immediate release (anomalous diffusion) stimulated by softening of the polymer matrix.

Correlation between some thermo-mechanical and physico-chemical properties in multi-component glasses of Se-Te-Sn-Cd system

The glass transition phenomenon is guided by the swift cooling of a melt (glass-forming liquid). Consequently, the glass as a final product consists of a considerable number of micro-voids having the size of the order of atomic and/or molecular sizes. The model of free volume fluctuation helps in describing the diverse physico-chemical properties of amorphous materials (like glasses and polymers). This theory is based on the fraction of fluctuation free frozen at the glass transition temperature and it forms a basis for determination of various significant thermo-mechanical properties. In the present work, Vickers hardness test method is employed that provides useful information concerning the mechanical behavior of brittle solids. The present work emphasizes the results of micro-indentation measurements on recently synthesized novel Se78−x Te20Sn2Cd x glassy system. Basic thermo-mechanical parameters such as micro-hardness, volume (V h), formation energy (E h) of micro-voids in the glassy network and modulus of elasticity (E) have been determined and their variation with glass composition has been investigated.

Correlation between flow units and crystallization in metallic glasses

The relationship between metastable and intrinsic inhomogeneous amorphous structure and the crystallization of metallic glasses (MGs) is not yet well explored. We have found a correlation between the flow unit, which can model the structural heterogeneity and explain the thermal relaxations, glass transition and plastic deformation phenomenon in MGs, and enthalpy of crystallization of MGs. The results help to understand the atomic scale evolution during nucleation and growth in the crystallization process and the nature of metallic glass.

Ordering and dimensional crossovers in metallic glasses and liquids

The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu46Zr54, Ni80Al20, Ni33.3Zr66.7, and Pd82Si18. Resulting cumulative coordination numbers (CN) show that metallic liquids have a dimension of d = 2.55 +/- 0.06 from the center atom to the first coordination shell and metallic glasses have d = 2.71 +/- 0.04, both less than 3. Between the first and second coordination shells, both phases crossover to a dimension of d = 3, as for a crystal. Observations from discrete atom center-of-mass position counting are corroborated by continuously counting Cu glass- and liquid-phase atoms on an artificial grid, which accounts for the occupied atomic volume. Results from Cu grid analysis show short-range d = 2.65 for Cu liquid and d = 2.76 for Cu glass. Cu grid structures crossover to d = 3 at {\xi}~8 {\AA} (~3 atomic diameters). We study the evolution of local structural dimensions during quenching and discuss its correlation with the glass transition phenomenon.