Glass Transition Behavior Research Articles

Thermodynamic re-optimisation of the CaO-FeO-Fe2O3 system integrated with experimental phase equilibria studies (Part II – Thermodynamic optimisation)

The Ca-Fe-O system is essential for understanding the chemical equilibria involved in copper production using calcium ferrite slags. It forms a core component of a complex 20-component Cu-Pb-Zn-Fe-Ca-Si-O-S-Al-Mg-Cr-Na-As-Sn-Sb-Bi-Ag-Au-Ni-Co system developed for diverse applications in ferrous and non-ferrous metallurgy. This study re-evaluates the Ca-Fe-O system using recent experimental phase equilibrium data acquired by the authors [1] through advanced equilibration, quenching, and Electron Probe X-ray Microanalysis (EPMA) techniques. Thermodynamic properties of solid phases have been revised in accordance with the recommendations for the third generation of Calphad databases. Liquid endmember heat capacities have been refined to describe glass transition behaviour in supercooled liquids. The updated properties of liquid endmembers significantly extend the applicability of the database, enabling lower-temperature applications related to toxic element leaching from amorphous and partially crystallized slags. The revised, higher melting temperature of CaO enhances predictive accuracy in multicomponent systems. Liquid slag phase has been modelled within the Modified Quasichemical Formalism to account for short-range ordering phenomena. Recent advances in modelling and optimization technique made it possible to assess experimental data within the Ca-Fe-O system as an integral part of a large multicomponent dataset, applicable for industrial conditions.

Thickness-Dependent Segmental Dynamics in Supported Thin Films: Insights from a Dynamically Correlated Network Model.

A large body of experimental studies shows that the local dynamics in supercooled liquids are significantly altered by spatial nanoconfinement. In a previous study, we proposed a concept of a dynamically correlated network (DCN) model, which assumes that segments in a supercooled liquid undergo cooperative rearrangements within a network-like cluster. We further demonstrated that a model modified for freestanding thin films can predict for the glass transition dynamics in atactic polystyrene (PS) films consistent with experimental results. In this study, we adapted the model to apply it to supported thin films by introducing a layer of virtual vacant segments at the free surface and virtual anchoring segments at the liquid/substrate interface. The latter segments, carrying a finite number of virtual segments, reduce mobility at the interface. We evaluated the cooperative cluster size and distribution with respect to temperature and film thickness, along with the average relaxation time and glass transition temperature Tg for supported thin films of PS. The model predicted that the thickness dependence of Tg for PS becomes stronger with increasing time scale, and this result agreed well with experimental data across different timescales from pseudothermodynamic and dynamic measurements. The results provide insights into the origin of the dynamical decoupling between pseudothermodynamic and dynamic glass transition behaviors.

Poly(ethylene oxide) bis(cyclic carbonate) based hydrophilic non-isocyanate polyhydroxyurethanes: Polymer-water interactions and glass transition behavior

Hydrogen bonding, glass transition, water absorption, and plasticization are studied as a function of hydrogen bond donor concentration in the chain of a non-isocyanate polyhydroxyurethane system, synthesized by solvent-free aminolysis of a poly(ethylene oxide) (PEO) based cyclic carbonate. The concentration of hydrogen bond donors is controlled by varying the ratio of diaminobutane (DAB) and triethylenetetramine (TETA) in the amine component. Introduction of secondary amino groups enhances hydrogen bonding and rigidity of the chain, and, as a result, slows down dynamics, as evidenced by an increase in glass transition temperature. Hydroxyurethane groups are the primary hydration sites despite the hydrophilicity of the polyether. Secondary amino groups act as secondary hydration sites which further increases water sorption capacity. The Couchman-Karasz model describes excellently the dependence of glass transition temperature on composition in both dry and hydrated systems.

High-entropy non-covalent cyclic peptide glass.

Biomolecule-based non-covalent glasses are biocompatible and biodegradable, and offer a sustainable alternative to conventional glass. Cyclic peptides (CPs) can serve as promising glass formers owing to their structural rigidity and resistance to enzymatic degradation. However, their potent crystallization tendency hinders their potential in glass construction. Here we engineered a series of CP glasses with tunable glass transition behaviours by modulating the conformational complexity of CP clusters. By incorporating multicomponent CPs, the formation of high-entropy CP glass is facilitated, which-in turn-inhibits the crystallization of individual CPs. The high-entropy CP glass demonstrates enhanced mechanical properties and enzyme tolerance compared with individual CP glass and a unique biorecycling capability that is unattainable by traditional glasses. These findings provide a promising paradigm for the design and development of stable non-covalent glasses based on naturally derived biomolecules, and advance their application in pharmaceutical formulations and smart functional materials.

Strain glass transition in Ti48Ni50Co2 alloy

Limited studies have been conducted on the impact of the Ni/Ti ratio on the strain glass (STG) transition behavior in TiNiCo alloys. For this work, Ti50-xNi48+xCo2 (x = 1, 2) alloys with varying Ni/Ti ratios are prepared to investigate the microstructural evolution, temperature-dependent electrical resistivity, and dynamic mechanical characteristics. It was found that no martensitic transformation occurs in Ti48Ni50Co2 owing to the increasing Ni/Ti ratio, but instead a STG transition was confirmed by the existence of nanodomains. Consequently, a continuous softening of storage moduli over a broad temperature range was observed.

Advancements in Novel Mechano-Rheological Probes for Studying Glassy Dynamics in Nanoconfined Thin Polymer Films.

The nanoconfinement effects of glassy polymer thin films on their thermal and mechanical properties have been investigated thoroughly, especially with an emphasis on its altered glass transition behavior compared to bulk polymer, which has been known for almost three decades. While research in this direction is still evolving, reaching new heights to unravel the underlying physics of phenomena observed in confined thin polymer films, we have a much clearer picture now. This, in turn, has promoted their application in miniaturized and functional applications. To extract the full potential of such confined films, starting from their fabrication, function, and various applications, we must realize the necessity to have an understanding and availability of robust characterization protocols that specifically target thin film thermo-mechanical stability. Being nanometer-sized in thickness, often atop a solid substrate, direct mechanical testing on such films becomes extremely challenging and often encounters serious complexity from the dominating effect of the substrate. In this review, we have compiled together a few important novel and promising techniques for mechano-rheological characterization of glassy polymer thin films. The conceptual background involved in each technique, constitutive equations, methodology, and current status of research are touched upon following a pedagogical tutorial approach. Further, we discussed each technique's success and limitations, carefully covering the puzzling or contradicting observations reported within the broad nexus of glass transition temperature-viscosity-modulus-molecular mobility (including diffusion and relaxation).

A dynamic phase separation model for glass transition behavior in water-triggered shape memory polymer towards programmable recovery onset

Water-triggered shape memory polymers (SMPs) have been extensively studied for biomedical applications due to their advantages of non-thermal actuation capability. However, few studies have been carried out to explore the working principle of shape recovery onset, which is essentially determined by the complex reactions between polymer macromolecules and water molecules. In this study, we developed a phase separation model to describe the dynamic glass transition in water-triggered SMPs. Based on the phase transition theory, dense and dilute phase separations of polymer macromolecules can be achieved when the dynamic diffusions of water molecules in the SMPs undergo dehydration and absorption processes, respectively. Then, the dynamic glass transition is resulted from the dehydration and absorption of water molecules, leading to the dense and dilute phases in the SMPs. Therefore, a free-energy equation has been developed to characterize the recovery onset, in which the mixing free energy and elastic free energy are originated from the Flory–Huggins solution theory and phase separation model, respectively. Moreover, the glass transition and its connection to shape recovery behaviors, i.e. recovery ratio, relaxation time and dynamic mechanical modulus, have also been investigated, according to the Fick’s diffusion law. Meanwhile, onset of programmable recovery has been explained by the dynamic phase separation, based on the transpiration theory and permeability model. Finally, the proposed model is verified using the experimental results reported in the literature. This study is expected to provide a fundamental approach to formulate the constitutive relationship between the dynamic phase separation and programmable recovery onset in the water-triggered SMPs.

Effect of temperature on the mechanical behavior of glass fiber reinforced with hollow glass particle-filled epoxy composites

The design of marine ships and aircraft components with hollow glass particle-filled fiber-reinforced composites demands an understanding of their performance under outdoor conditions. The continuous glass fiber-reinforced epoxy matrix filled with hollow glass particles in the range of 0–0.3 vol fraction was prepared by the compression molding machine. The influence of temperature exposure on the mechanical behavior of glass fiber-reinforced hollow glass particle composites was studied by conducting tensile and flexural tests. The temperature exposure varying from room temperature up to 60 °C was used to investigate the effect of service temperature on the hollow glass particle-filled fiber composite specimens. Differential scanning calorimetry (DSC) analysis was conducted to study the glass transition behavior of the composites. The incorporation of microspheres in the glass fiber composites gradually reduced the tensile and flexural strength, while their specific values increased as increasing the microspheres. The hollow glass particle-filled fiber composites tested at 60 °C exhibited a decrease in tensile and flexural strength compared with room temperature. As the température of the test spécimens was nearer to the glass transition value, the polymer chain was softened, leading to a reduction in strength. In contrast, the modulus values remain unaffected by increasing the temperature to 60 °C.

The glass transition and enthalpy recovery of polystyrene nanorods using Flash differential scanning calorimetry.

The glass transition (Tg) behavior and enthalpy recovery of polystyrene nanorods within an anodic aluminum oxide (AAO) template (supported nanorods) and after removal from AAO (unsupported nanorods) is studied using Flash differential scanning calorimetry. Tg is found to be depressed relative to the bulk by 20 ± 2K for 20 nm-diameter unsupported polystyrene (PS) nanorods at the slowest cooling rate and by 9 ± 1K for 55 nm-diameter rods. On the other hand, bulk-like behavior is observed in the case of unsupported 350 nm-diameter nanorods and for all supported rods in AAO. The size-dependent Tg behavior of the PS unsupported nanorods compares well with results for ultrathin films when scaled using the volume/surface ratio. Enthalpy recovery was also studied for the 20 and 350nm unsupported nanorods with evolution toward equilibrium found to be linear with logarithmic time. The rate of enthalpy recovery for the 350nm rods was similar to that for the bulk, whereas the rate of recovery was enhanced for the 20nm rods for down-jump sizes larger than 17K. A relaxation map summarizes the behavior of the nanorods relative to the bulk and relative to that for the 20 nm-thick ultrathin film. Interestingly, the fragility of the 20 nm-diameter nanorod and the 20nm ultrathin film are identical within the error of measurements, and when plotted vs departure from Tg (i.e., T - Tg), the relaxation maps of the two samples are identical in spite of the fact that the Tg is depressed 8K more in the nanorod sample.

The thermo-optical coefficient as an alternative probe for the structural arrest of polymeric glass formers

The most important, yet independent susceptibilities to characterize the canonical glass transition include the thermal expansion, the specific heat and the shear modulus. At the glass transition, all these susceptibilities show a step-like behaviour as a function of temperature. However, in principle, different susceptibilities provide different perspectives on the glass transition. Due to the effect of sample history and considerable kinetic influences on the thermal glass transition behaviour, the best way to evaluate these different perspectives is to investigate them simultaneously. In this publication, different perspectives on the dynamical freezing process are obtained by a single experimental method: Temperature-modulated optical refractometry (TMOR). TMOR is used to simultaneously investigate the dynamic thermal expansion and, indirectly, the shear viscosity of a model polymer, both contributing to the thermo-optical coefficient. It will be discussed how this thermo-optical property couples to the structural arrest designated as one of the characteristics of the solidification process of polymers.

Dynamic Viscoelastic Properties of Kenaf Fiber Reinforced Shape Memory Polymer Composites

This paper comprehensively investigates the dynamic viscoelastic behavior of shape memory polymer composites (SMPCs) reinforced with different weight percentages of kenaf fiber (KF) ranging from 0%, 5%, 10%, 15%, 20%, 30% and 40%. The dynamic mechanical behavior of these composites was characterized using dynamic mechanical analysis (DMA) over a range of temperatures. The objective was to determine the optimal fiber content of KF as reinforcement in SMPCs, specifically on viscoelastic response, storage modulus, loss modulus, damping and glass transition behaviour. The results revealed a clear correlation between the KF contents and the dynamic mechanical properties of SMPCs. The storage modulus significantly improves at higher KF content, particularly at elevated temperatures. Additionally, a quantitative assessment of coefficient C demonstrates strong interfacial bonding between fibers and the matrix in samples 30KF and 40KF. These samples also exhibit higher loss modulus and lower tan delta values, providing evidence for the efficacy of KF in enhancing composite properties. Moreover, higher KF contents induce a shift in the glass transition temperature, signifying enhanced in fiber-matrix interaction and thermal stability. The Cole-cole further demonstrates that at higher KF content, the sample surpasses Neat SMPU, presenting compelling evidence of improved matrix-fiber bonding. Statistical analysis through one-way analysis of variance (ANOVA) substantiates the statistical significance of the dynamic mechanical properties across the different weight percentages of KF-SMPCs. Based on these findings, 30KF is the optimal fiber content, balancing mechanical enhancement and feasible fabrication. This decision is grounded in challenges encountered at 40KF, where ensuring composite homogeneity becomes complex. This study contributes to the growing body of knowledge on utilization of natural fibers in development of advanced polymer composites while maintaining eco-sustainability.

Effect of Asymmetric Lobe Size on the Molecular Dynamics, Glass Transition, and Dielectric Behavior in Janus Nanoparticles

Effect of Asymmetric Lobe Size on the Molecular Dynamics, Glass Transition, and Dielectric Behavior in Janus Nanoparticles

Investigation of the isothermal curing and glass transition behaviors of epoxy–imidazole systems

The isothermal curing behavior of an epoxy–imidazole system was investigated through thermal, mechanical, and compositional analyses. Precise control over temperature and time afforded the monitoring of the progression of the curing reaction and enthalpy relaxation via fast scanning calorimetry. The real-time tracking of the glass transition temperature (Tg) during isothermal curing revealed a temperature-dependent relationship between Tg and thermally estimated conversion, distinct from epoxy–amine systems. Unlike previous research suggesting plasticization through cyclic-compound formation in epoxy–imidazole systems, such compounds were not detected in the early curing stages in this study. Furthermore, an endothermic reaction from imidazole regeneration was suggested to overlap with the main exothermic reaction of polymerization. Therefore, assessing thermally estimated conversion in the intermediate curing stage through differential scanning calorimetry was deemed practically impossible for epoxy–imidazole systems. The Tg values of resins with different thermal histories were equal after complete curing under high-temperature/long-duration conditions.

Structural investigation and thermal properties of Al2O3-PbO-B2O3 glasses

Two series of aluminum lead borate glasses, (Al2O3)y(PbO)35-y(B2O3)65 and (Al2O3)y(PbO)70-y(B2O3)30, were prepared and effect of PbO → Al2O3 substitution on their structure and thermal properties was studied. The semi-quantitative analysis of the Raman spectroscopy data was used to structural interpretation of glass transition behavior in the Al2O3-doped lead borate glasses. The mechanisms of structural reorganization of glassy network under PbO → Al2O3 substitution were found to differ for the studied series although Al3+ ions are incorporated in the glass network, mainly, in form of AlO4 units in the both cases. The formation of AlO4 tetrahedra is accompanied by transformation of various isolated borate anions into finite-sized metaborate chains as well as the conversion of four-fold coordinated [BØ3O−]− species with one non-bridging oxygen atom into fully polymerized [BØ4]− tetrahedra in the (Al2O3)y(PbO)70-y(B2O3)30 glasses. In the series of glasses with high concentration of B2O3, B[4] → B[3] transformation including the shift of [BØ4]− ↔ BØ2O− equilibrium toward the right side is the main process of structural reorganization caused by PbO → Al2O3 substitution. In this case, the change in the network connectivity is determined by competition between increasing the amount of Al-O-B bonds against the background of decreasing the amount of B-O-B bonds between borate structural species. In the B-poor series, the glass transition temperature increased with Al2O3 from 280 to 360 °C, and the crystallization peak onset occurs at 340 and 380 °C for the glasses with the 0 and 3 mol.% Al2O3 contents, respectively (higher aluminum oxide contents already prevent crystallization). In the B-rich series, Tg increases with the Al2O3 content from 430 to 490 °C, and the crystallization occurs at 560 °C only for the Al2O3-free glass. The structural relaxation behavior in the glass transition rage was described in terms of the Tool-Narayanaswamy-Moynihan model. The activation energy for the relaxation movements was found to be non-monotonous in case of both compositional series.

Interparticle interaction-dependent jamming in colloids: insights into glass transition and morphology modulation during rapid evaporation-induced assembly.

Understanding the role of interparticle interactions in jamming phenomena is essential for gaining insights into the intriguing glass transition behavior observed in atomic and molecular systems. In this study, we investigate the jamming behavior of colloids with tunable interparticle interactions during evaporation-induced assembly (EIA). By manipulating the interaction among charged colloids using cationic polyethyleneimine (PEI) through electro-sorption and subsequent free polymer induced repulsion, we observe distinct jamming behavior in silica colloids during EIA, depending on the interparticle interactions. Silica colloids with strong repulsive interactions exhibit a repulsive colloidal glass state with a volume fraction of silica colloids in supraparticle ϕ ∼ 0.70. On the other hand, PEI-mediated attractive interactions among silica colloids lead to an attractive colloidal glass phase with a significantly lower ϕ ∼ 0.43. Free polymer induced repulsion of colloids at higher PEI concentration once again results in a repulsive glassy state with ϕ ∼ 0.61. Furthermore, we revealed that interparticle interactions not only influence the jamming behavior but also play a significant role in shaping the morphology of self-assembled structures during EIA, and the assembled structure undergoes a morphological reentrant transition from a doughnut-like shape to a spherical form and again back to a doughnut-like configuration. Jamming-dependent evolution of micropores and dynamics of the confined PEI have been probed using positron annihilation lifetime spectroscopy (PALS) and broadband dielectric spectroscopy (BDS). PALS reveals distinct variations in the micropores of the supraparticles with different PEI loadings, confirming the impact of jamming on the evolution of the micropores within the supraparticles. BDS measurements uncover non-monotonic dynamics of PEI molecules confined in the evolved pore network. It is revealed that the reentrant jamming behavior of colloids, modulated by PEI, holds profound significance for the long-term stability of supraparticles.

Mechanochemically-induced glass formation from two-dimensional hybrid organic-inorganic perovskites.

Hybrid organic-inorganic perovskites (HOIPs) occupy a prominent position in the field of materials chemistry due to their attractive optoelectronic properties. While extensive work has been done on the crystalline materials over the past decades, the newly reported glasses formed from HOIPs open up a new avenue for perovskite research with their unique structures and functionalities. Melt-quenching is the predominant route to glass formation; however, the absence of a stable liquid state prior to thermal decomposition precludes this method for most HOIPs. In this work, we describe the first mechanochemically-induced crystal-glass transformation of HOIPs as a rapid, green and efficient approach for producing glasses. The amorphous phase was formed from the crystalline phase within 10 minutes of ball-milling, and exhibited glass transition behaviour as evidenced by thermal analysis techniques. Time-resolved in situ ball-milling with synchrotron powder diffraction was employed to study the microstructural evolution of amorphisation, which showed that the crystallite size reaches a comminution limit before the amorphisation process is complete, indicating that energy may be further accumulated as crystal defects. Total scattering experiments revealed the limited short-range order of amorphous HOIPs, and their optical properties were studied by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy.

Effect of overheating-induced minor addition on Zr-based metallic glasses

Melt treatment is well known to have an important influence on the properties of metallic glasses (MGs). However, for the MGs quenched from different melt temperatures with a quartz tube, the underlying physical origin responsible for the variation of properties remains poorly understood. In the present work, we systematically studied the influence of melt treatment on the thermal properties of a Zr50Cu36Al14 glass-forming alloy and unveiled the microscopic origins. Specifically, we quenched the melt at different temperatures ranging from 1.1T l to 1.5T l (T l is the liquidus temperature) to obtain melt-spun MG ribbons and investigated the variation of thermal properties of the MGs upon heating. We found that glass transition temperature, T g, increases by as much as 36 K, and the supercooled liquid region disappears in the curve of differential scanning calorimetry when the melt is quenched at a high temperature up to 1.5T l. The careful chemical analyses indicate that the change in glass transition behavior originates from the incorporation of oxygen and silicon in the molten alloys. The incorporated oxygen and silicon can both enhance the interactions between atoms, which renders the cooperative rearrangements of atoms difficult, and thus enhances the kinetic stability of the MGs.

Physical origin of the second damping peak in ionomers as traced by enthalpy relaxation

Ionomers possess two loss factor peaks, thus providing a possibility for the fabrication of novel damping materials. Eisenberg et al. assigned the second damping peak to the glass transition of restricted regions in the ionic cluster. However, the ordinary heat flow curves showed only one glass transition corresponding to the first loss factor peak. Moreover, the conventional view by multiplet/cluster model has been questioned by Simmons due to their different conclusions on the size of restricted regions (Macromolecules 2015, 48, 2313−2323). Meanwhile, we found that the storage modulus of the second damping peak was right in the modulus range of the Rouse relaxation mode. In view of these confusions, enthalpy relaxation characteristics were investigated to clarify the nature of the second loss factor peak. It was found that all the ionomers possessed anomalous enthalpy hysteresis due to the existence of two different but partly coupled glass transitions, while Rouse motion did not cause anomalous enthalpy hysteresis. Furthermore, the heat capacity curves after physical aging clearly showed two glass transition behaviors. These experimental evidences confirmed that the second loss factor peak originated from the glass transition in cluster rather than Rouse relaxation, thus further validating the view by multiplet/cluster model.

Design and Investigation of a Side-Chain Liquid Crystalline Polysiloxane with a Ntb-Phase-Forming Side Chain

A new mesogenic non-symmetric dimeric monomer with a terminal olefin function, forming a twist bend nematic (Ntb) as well as a nematic (N) phase, was synthesized, using an enhanced synthetic methodology, which avoids isomerization of the terminal double bond in the preparation of the dimer. This monomer was attached to a pentamethyldisiloxane group, resulting in the SmA LC phase behavior of the ensuing material. Linking the monomer to a siloxane main chain resulted in nematic phase behavior. Detailed studies with the Ntb phase forming dimer DTC5C7 show full miscibility of the dimer and the new LC polymer in the LC state, suggesting that the side-chain LC polymer forms a Ntb phase as the low-temperature nematic phase. Copolymerizing the monomer with a cyanobiphenyl-based monomer allows us to tune the glass transition and phase behavior further.

A redox effect on the viscosity of molten pyrolite

The viscosity of molten Earth mantle has been determined for various redox states using very high temperature viscometry at 1 bar. The viscosity-temperature relationship of the most oxidised pyrolite studied here is comparable to that of a previous determination of the viscosity of a peridotite melt. For the first time, the effect of iron redox state on molten mantle viscosity has been determined by calorimetric analysis of the glass transition on extremely carefully characterised glassy samples quenched from conditions of variable fO2 using gas-mixing levitation. There is a clear trend of decreasing viscosity with increasing redox state over the range of Fe3+/ΣFe. = 0.07–0.29. We also observe an increase in glass transition temperatures with increasing melt depolymerisation (i.e., higher NBO/T ratios). Both the negative oxidation dependence of viscosity and glass transition behaviour upon depolymerisation are contradictory to the trends observed from redox viscometry of more silica-rich melts but may be consistent with the broadly diminishing positive redox viscometry trends of melts with increasing basicity.