Showing papers on "Glass transition published in 2020"
TL;DR: In this article, a 3D copper nanowires-thermally annealed graphene aerogel (CuNWs-TAGA) framework is firstly prepared by freeze-drying followed by thermal annealing from CuNWs, graphene oxide (GO) and Lascorbic acid.
Abstract: 3D copper nanowires-thermally annealed graphene aerogel (CuNWs-TAGA) framework is firstly prepared by freeze-drying followed by thermal annealing from CuNWs, graphene oxide (GO) and L-ascorbic acid. Epoxy resin is then poured back into the above 3D CuNWs-TAGA framework to fabricate the CuNWs-TAGA/epoxy nanocomposites. CuNWs with average diameter of about 120 nm and length of approximate 10 μm are successfully prepared. When the mass fraction of CuNWs-TAGA is 7.2 wt% (6.0–1.2 wt% CuNWs-TAGA), the thermal conductivity coefficient (λ) value of the CuNWs-TAGA/epoxy nanocomposites reaches the maximum of 0.51 W/mK. Meantime, the CuNWs-TAGA/epoxy nanocomposites exhibit the maximum electromagnetic interference shielding effectiveness (EMI SE) value of 47 dB and electrical conductivity (σ) of 120.8 S/m, ascribed to perfect 3D CuNWs-TAGA conductive network structures. Meanwhile, the corresponding elasticity modulus, hardness, glass transition temperature (Tg) and heat-resistance index (THRI) of the CuNWs-TAGA/epoxy nanocomposites increase to 4.69 GPa, 0.33 GPa, 126.3 °C and 181.7 °C, respectively.
482 citations
TL;DR: In this article, a thermally conductive thermal interface material (TIM) was fabricated by vertical freezing the solution of carbon fibers and then freeze-dying to remove the ice and then infiltrate them with epoxy resin matrix.
180 citations
TL;DR: It is revealed that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of “free” and associated complementary moieties of hydrogen bonds, enabling network reconfiguration in theGlassy polymer.
Abstract: Glassy polymers are extremely difficult to self-heal below their glass transition temperature (Tg) due to the frozen molecules. Here, we fabricate a series of randomly hyperbranched polymers (RHP) with high density of multiple hydrogen bonds, which show Tg up to 49 °C and storage modulus up to 2.7 GPa. We reveal that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of “free” and associated complementary moieties of hydrogen bonds. The free complementary moieties can exchange with the associated hydrogen bonds, enabling network reconfiguration in the glassy polymer. As a result, the RHP shows amazing instantaneous self-healing with recovered tensile strength up to 5.5 MPa within 1 min, and the self-healing efficiency increases with contacting time at room temperature without the intervention of external stimuli.
107 citations
TL;DR: It is shown that ζ correlates strongly to the glass transition temperature, and that this simple method predicts the T g with a root-mean-square error of 13 °C for conjugated polymers with alkyl side chains.
Abstract: The glass transition temperature (Tg) is a key property that dictates the applicability of conjugated polymers. The Tg demarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. Here we show that a single adjustable parameter can be used to build a relationship between the Tg and the molecular structure of 32 semiflexible (mostly conjugated) polymers that differ drastically in aromatic backbone and alkyl side chain chemistry. An effective mobility value, ζ, is calculated using an assigned atomic mobility value within each repeat unit. The only adjustable parameter in the calculation of ζ is the ratio of mobility between conjugated and non-conjugated atoms. We show that ζ correlates strongly to the Tg, and that this simple method predicts the Tg with a root-mean-square error of 13 °C for conjugated polymers with alkyl side chains. The glass transition temperature (Tg) is a key property that dictates the applicability of conjugated polymers. Here the authors use one adjustable parameter to build a relationship between the Tg and the molecular structure of semiflexible polymers that differ in aromatic backbone and alkyl side chain chemistry.
97 citations
TL;DR: In this article, a catalysts free graphene oxide (GO) promoted self-healing vitrimer nanocomposites are designed, where the synthesized vitrimers displays selfhealing properties via disulfide exchange based covalent adaptive network behavior.
Abstract: Catalyst free graphene oxide (GO) promoted self-healing vitrimer nanocomposites are designed, where the synthesized vitrimer nanocomposites displays self-healing properties via disulfide exchange based covalent adaptive network behavior. This study found that GO based nanofiller enhance the self-healing properties, including the shape memory and flexural strength of the materials. The GO induced lower glass transition was helpful to achieve low temperature self-healing: when compared to epoxy vitrimers (73% and 60% self-healing) the vitrimeric nanocomposites demonstrates a 88% and 80% self-healing for the first and second cycle, respectively.
78 citations
TL;DR: In this paper, the three-dimensional carbon fiber (CF)-MXenes foam, in which the vertically aligned CF constructed the heat transport paths, were prepared by simple freeze-drying method.
75 citations
TL;DR: Variation in NCC concentration and interparticle forces can explain the complex phase behaviours observed within suspensions formulated using NCC obtained from different sources, validates a key hypothesis for the study of NCC suspensions.
63 citations
TL;DR: It was found that, contrary to expectations, ASDs with drug-polymer hydrogen bonding exhibited poorer initial release at moderate drug loadings as compared to the non-hydrogen bonding analog ASDs, and surface crystallization led to deterioration of dissolution performance.
Abstract: Drug loading is an important parameter known to impact the release rate of a poorly soluble drug from an amorphous solid dispersion (ASD). Recent studies have shown that small increases in drug loading can dramatically reduce the drug release rate from ASDs prepared with poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA). However, the link between drug physicochemical properties and the drug loading where the release is abruptly compromised is not well understood. This study probes the role of different factors on the relative dissolution rates of drug and polymer from PVPVA-based ASDs as a function of drug loading: (1) the impact of drug-polymer hydrogen bonding interactions on the initial dissolution rate of ASDs, investigated using two structural analogues, indomethacin (IND) and indomethacin methyl ester (INDester), (2) the influence of surface drug crystallization, observed for INDester ASDs, and (3) by changing temperature, the impact of the "wet" glass transition temperature (Tg). Scanning electron microscopy (SEM), with or without energy dispersive X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FTIR), and powder X-ray diffraction (PXRD) were utilized to study the solid-state phase behavior and/or drug enrichment on the partially dissolved ASD tablet surfaces. Nanoparticle tracking analysis (NTA) was utilized to study the solution-state phase behavior. It was found that, contrary to expectations, ASDs with drug-polymer hydrogen bonding exhibited poorer initial release at moderate drug loadings (15-25%) as compared to the non-hydrogen bonding analogue ASDs. Surface crystallization led to the deterioration of dissolution performance. Lastly, Tg relative to experimental temperatures also appeared to play a role in the observed dissolution behavior as a function of drug loading. These findings shed light on potential mechanisms governing ASD dissolution performance and will aid in the development of optimized ASD formulations with enhanced dissolution performance.
62 citations
TL;DR: Vegetable oil-based polymeric materials always suffer from relatively poor performance, such as lower tensile strength and glass transition temperatures, than petroleum-based materials, w... as mentioned in this paper.
Abstract: Vegetable oil-based polymeric materials always suffer from relatively poor performance, such as lower tensile strength and glass transition temperatures, than petroleum-based polymeric materials, w...
60 citations
TL;DR: It is shown that in dense solutions of circular polymers containing (active) segments of increased mobility, the interplay of the activity and the topology of the polymers generates an unprecedented glassy state of matter, namely active topological glass.
Abstract: The glass transition in soft matter systems is generally triggered by an increase in packing fraction or a decrease in temperature. It has been conjectured that the internal topology of the constituent particles, such as polymers, can cause glassiness too. However, the conjecture relies on immobilizing a fraction of the particles and is therefore difficult to fulfill experimentally. Here we show that in dense solutions of circular polymers containing (active) segments of increased mobility, the interplay of the activity and the topology of the polymers generates an unprecedented glassy state of matter. The active isotropic driving enhances mutual ring threading to the extent that the rings can relax only in a cooperative way, which dramatically increases relaxation times. Moreover, the observed phenomena feature similarities with the conformation and dynamics of the DNA fibre in living nuclei of higher eukaryotes. Glass transition in soft materials can be affected by the topology of constituent particles, but the detail remains elusive. Here, Smrek et al. show that the interplay between circular topology of ring polymers and their active segments generates a new state of matter, namely active topological glass.
60 citations
Journal Article•
TL;DR: In this paper, the authors used a single adjustable parameter to build a relationship between the glass transition temperature and the molecular structure of 32 semi-lexible polymers that differ drastically in aromatic backbone and alkyl side chain chemistry.
Abstract: The glass transition temperature ( T g ) is a key property that dictates the applicability of conjugated polymers. The T g demarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. Here we show that a single adjustable parameter can be used to build a relationship between the T g and the molecular structure of 32 semiflexible (mostly conjugated) polymers that differ drastically in aromatic backbone and alkyl side chain chemistry. An effective mobility value, ζ , is calculated using an assigned atomic mobility value within each repeat unit. The only adjustable parameter in the calculation of ζ is the ratio of mobility between conjugated and non-conjugated atoms. We show that ζ correlates strongly to the T g , and that this simple method predicts the T g with a root-mean-square error of 13 °C for conjugated polymers with alkyl side chains. The glass transition temperature (Tg) is a key property that dictates the applicability of conjugated polymers. Here the authors use one adjustable parameter to build a relationship between the Tg and the molecular structure of semiflexible polymers that differ in aromatic backbone and alkyl side chain chemistry.
TL;DR: It is reported that electrolytes composed of the cyclic liquid ether, dioxolane (DOL), and containing the simple salt LiNO3 are able to completely bypass the liquid → crystalline solid thermal transition, and to exhibit abnormally high bulk and interfacial ionic conductivities down to temperatures as low as −50 °C.
Abstract: In the presence of Lewis acid salts, the cyclic ether, dioxolane (DOL), is known to undergo ring-opening polymerization inside electrochemical cells to form solid-state polymer batteries with good interfacial charge-transport properties. Here we report that LiNO3, which is unable to ring-open DOL, possesses a previously unknown ability to coordinate with and strain DOL molecules in bulk liquids, completely arresting their crystallization. The strained DOL electrolytes exhibit physical properties analogous to amorphous polymers, including a prominent glass transition, elevated moduli, and low activation entropy for ion transport, but manifest unusually high, liquidlike ionic conductivities (e.g., 1 mS/cm) at temperatures as low as −50 °C. Systematic electrochemical studies reveal that the electrolytes also promote reversible cycling of Li metal anodes with high Coulombic efficiency (CE) on both conventional planar substrates (1 mAh/cm2 over 1,000 cycles with 99.1% CE; 3 mAh/cm2 over 300 cycles with 99.2% CE) and unconventional, nonplanar/three-dimensional (3D) substrates (10 mAh/cm2 over 100 cycles with 99.3% CE). Our finding that LiNO3 promotes reversibility of Li metal electrodes in liquid DOL electrolytes by a physical mechanism provides a possible solution to a long-standing puzzle in the field about the versatility of LiNO3 salt additives for enhancing reversibility of Li metal electrodes in essentially any aprotic liquid electrolyte solvent. As a first step toward understanding practical benefits of these findings, we create functional Li||lithium iron phosphate (LFP) batteries in which LFP cathodes with high capacity (5 to 10 mAh/cm2) are paired with thin (50 μm) lithium metal anodes, and investigate their galvanostatic electrochemical cycling behaviors.
TL;DR: In this paper, a novel zinc vanadyl boro-phosphate glasses with nominal compositions 46V2O5-46P2O 5 −8-x B2O3-x ZnO (x = 0-8mol %) have been synthesized and coded as VPB8, VPB6Zn2, VPBF4Zn4, VPB2Zn6, and VPZn8, respectively.
TL;DR: It is suggested that the shadow glass transition signals the thermodynamics of β relaxation in hyper-quenched metallic glasses.
Abstract: One puzzling phenomenon in glass physics is the so-called 'shadow glass transition' which is an anomalous heat-absorbing process below the real glass transition and influences glass properties. However, it has yet to be entirely characterized, let alone fundamentally understood. Conventional calorimetry detects it in limited heating rates. Here, with the chip-based fast scanning calorimetry, we study the dynamics of the shadow glass transition over four orders of magnitude in heating rates for 24 different hyper-quenched metallic glasses. We present evidence that the shadow glass transition correlates with the secondary (β) relaxation: (i) The shadow glass transition and the β relaxation follow the same temperature-time dependence, and both merge with the primary relaxation at high temperature. (ii) The shadow glass transition is more obvious in glasses with pronounced β relaxation, and vice versa; their magnitudes are proportional to each other. Our findings suggest that the shadow glass transition signals the thermodynamics of β relaxation in hyper-quenched metallic glasses.
TL;DR: In this article, the role of temperature and strain rate in the mechanical behavior of polyether-ether-ketone (PEEK) was investigated. And a constitutive model was proposed to explain the experimental observations by means of entropic strain hardening due to reorientation of polymer chains influenced by thermo-viscoelastic effects.
TL;DR: An analysis of the impact of nanoconfinement on adsorption, and a perspective on future work where the key ideas of irreversibility, equilibration and long-range interactions are addressed.
Abstract: For almost a decade, growing experimental evidence has revealed a strong correlation between the properties of nanoconfined polymers and the number of chains irreversibly adsorbed onto nonrepulsive interfaces, e.g. the supporting substrate of thin polymer coatings, or nanofillers dispersed in polymer melts. Based on such a correlation, it has already been possible to tailor structural and dynamics properties – such as the glass transition temperature, the crystallization rate, the thermal expansion coefficients, the viscosity and the wettability – of nanomaterials by controlling the adsorption kinetics. This evidence indicates that irreversible adsorption affects nanoconfinement effects. More recently, also the opposite phenomenon was experimentally observed: nanoconfinement alters interfacial interactions and, consequently, also the number of chains adsorbed in equilibrium conditions. In this review we discuss this intriguing interplay between irreversible adsorption and nanoconfinement effects in ultrathin polymer films. After introducing the methods currently used to prepare adsorbed layers and to measure the number of irreversibly adsorbed chains, we analyze the models employed to describe the kinetics of adsorption in polymer melts. We then discuss the structure of adsorbed polymer layers, focusing on the complex macromolecular architecture of interfacial chains and on their thermal expansion; we examine the way in which the structure of the adsorbed layer affects the thermal glass transition temperature, vitrification, and crystallization. By analyzing segmental dynamics of 1D confined systems, we describe experiments to track the changes in density during adsorption. We conclude this review with an analysis of the impact of nanoconfinement on adsorption, and a perspective on future work where we also address the key ideas of irreversibility, equilibration and long-range interactions.
TL;DR: In this article, a new dynamic covalent chemistry based on siloxane equilibrium exchange into liquid crystalline elastomers (LCE) is introduced to enable processing (director alignment, remolding, and welding).
Abstract: Liquid crystalline elastomers (LCE) undergo reversible shape changes in response to stimuli, which enables a wide range of smart applications, in soft robotics, adhesive systems or biomedical medical devices. In this study, we introduce a new dynamic covalent chemistry based on siloxane equilibrium exchange into the LCE to enable processing (director alignment, remolding, and welding). Unlike the traditional siloxane based LCE, which were produced by reaction schemes with irreversible bonds (e.g. hydrosilylation), here we use a much more robust reaction (thiol-acrylate/thiol-ene ‘double-click’ chemistry) to obtain highly uniform dynamically crosslinked networks. Combining the siloxane crosslinker with click chemistry produces exchangeable LCE (xLCE) with tunable properties, low glass transition (−30 °C), controllable nematic to isotropic transition (33 to 70 °C), and a very high vitrification temperature (up to 250 °C). Accordingly, this class of dynamically crosslinked xLCE shows unprecedented thermal stability within the working temperature range (−50 to 140 °C), over many thermal actuation cycles without any creep. Finally, multiple xLCE sharing the same siloxane exchangeable bonds can be welded into single continuous structures to allow for composite materials that sequentially and reversibly undergo multiple phase transformations in different sections of the sample.
TL;DR: In this article, the perovskite quantum dots (QDs)-glass composite yields radioluminescence (RL), showing X-ray excited RL ∼ 1/18 to that of commercial Bi4Ge3O12 (BGO) single crystal.
Abstract: CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have emerged as a kind of brand-new X-ray scintillator with high performance. Herein, following the phase transformation from amorphous to crystalline, CsPb(Cl,Br)3 QDs are in-situ precipitated from a borate glass matrix. It is demonstrated for the first time that the perovskite QDs-glass composite yields radioluminescence (RL), showing X-ray excited RL ∼1/18 to that of commercial Bi4Ge3O12 (BGO) single crystal. The color of RL is adjustable, dependent on the anionic species. Evidently, the high power X-ray induced damage in material is recoverable just by re-heating it at glass transition temperature. This work highlights the partial settlement of tough issues in perovskite QDs as scintillators, such as, physical stability, service lifetime, Pb-toxicity, and production scale.
TL;DR: In this paper, the effects of the content of pickling sludge on crystalline properties of parent glass and physicochemical properties of glass-ceramics have been systematically discussed, and the gap between nucleation temperature and crystallization temperature can be narrowed with higher content of sludge, which caused fracture of the glass network (Si-O) and generation of the nonbridging oxygen (NBO), promoting the formation of diopside phase.
TL;DR: In this article, the authors evaluated the thermal properties and the kinetic parameters of TeO2-Li2O-ZnO-Nb2O5-Yb 2O3 glass series as a function of increasing Yb 2 O3 content.
Abstract: The thermal properties and the kinetic parameters of TeO2–Li2O–ZnO–Nb2O5–Yb2O3 glass series have been evaluated as a function of increasing Yb2O3 content. The theoretical elastic properties and the quantitative analysis (the link between the elastic features and the changed chemical composition of the glass) have been determined by the use of bond compression and Makishima–Mackenzie models. The thermal analysis Differential Scanning Calorimetry (DSC) test was used for estimating the glass characteristics temperatures, thermal stability, and non-isothermal kinetic parameters at the heating rates (β) 10, 15, 20 and 25 K/min. The activation energies of the glass transition 〈 Eg 〉 and crystallization 〈 Ec 〉 , as well as the order of the crystallization reaction (n), have been computed by different models with clear consistency and harmony between them. It was found that the characteristics temperatures of transition (Tg), softening (Ts), the onset of the crystallization (Tx) and the crystallization (Tc) increased with increasing the heating rate. Also, the results showed the higher thermal stability values (>100 K) for the understudied glass which is confirmed by KSP and ((Tc–Tg)/Tg) parameters values. Calculating of (n) showed that the crystallization started with surface nucleation and finished with bulk volume nucleation with rising Yb2O3 (mol %). The computed elastic moduli were linked with the interpretation of the thermal parameters to give a comprehensive image of the studied glass system.
TL;DR: In this article, a shuffle-nanodomain regulated strain glass transition in a metastable β-Ti alloy, Ti-24Nb-4Zr-8Sn (wt.%, Ti2448), is reported.
TL;DR: In this paper, a crosslinked gel polymer electrolyte by polymerization of methyl methacrylate with poly(ethylene glycol) dimethacrylated within a liquid electrolyte composed of an ethylene carbonate/propylene carbonates low volatility solvent mixture is presented.
TL;DR: It is shown that the time scale of the α-relaxation exhibits super-Arrhenius temperature dependence typical of fragile liquids, while vitrification kinetics displays milder temperature dependence at moderate undercooling, and thereby, vitrification takes place at temperatures lower than those associated to theα- Relaxation.
Abstract: Understanding how glasses form, the so-called vitrification, remains a major challenge in materials science. Here, we study vitrification kinetics, in terms of the limiting fictive temperature, and atomic mobility related to the α-relaxation of an Au-based bulk metallic glass former by fast scanning calorimetry. We show that the time scale of the α-relaxation exhibits super-Arrhenius temperature dependence typical of fragile liquids. In contrast, vitrification kinetics displays milder temperature dependence at moderate undercooling, and thereby, vitrification takes place at temperatures lower than those associated to the α-relaxation. This finding challenges the paradigmatic view based on a one-to-one correlation between vitrification, leading to the glass transition, and the α-relaxation. We provide arguments that at moderate to deep undercooling, other atomic motions, which are not involved in the α-relaxation and that originate from the heterogeneous dynamics in metallic glasses, contribute to vitrification. Implications from the viewpoint of glasses fundamental properties are discussed.
TL;DR: In this article, a 12-component asphalt model was employed in the molecular dynamics simulations with the modified Amber-Cornell force field to evaluate the thermal (glass transition temperature), transport (self-diffusion), and rheological (viscosity, storage and loss modulus) properties of asphalt via laboratory experiments and molecular dynamics simulation.
TL;DR: It was found that furan-bifuran copolyesters could be as effective, or better, oxygen barrier materials as neat PBF or PBBf, which themselves were found superior to common barrier polyesters such as PET.
TL;DR: In this article, the first observation of a reentrant glass transition in amorphous alloys was reported, where the supercooled liquid of the super-quenched glass transitions into a new glass, and the resulting lower-energy glass has its own glass transition temperature higher than that of Glass I by as much as 50 degrees.
TL;DR: In this paper, the effect of temperature curing conditions of the glass transition temperature of the epoxy polymer used for externally bonded strengthening system applied by wet lay-up methods is investigated.
TL;DR: In this paper, a networked solid polymer electrolyte (N-SPE) consisting of a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt as well as a polymer framework constructed using cage-like polyhedral oligomeric silsesquioxane (POSS) and serving as hubs to network poly(ethylene oxide-co-polypropylene oxide) (P(EO-co)-PO)) chains is presented.
TL;DR: For the first time, nano-scale aluminum hypophosphite (AlPO2) was simply obtained in a two-step milling process and applied in preparation of epoxy nanocomposites varying concentration and thermogravimetric analysis (TGA) showed that nanocomPOSites were thermally stable.
Abstract: For the first time, nano-scale aluminum hypophosphite (AlPO2) was simply obtained in a two-step milling process and applied in preparation of epoxy nanocomposites varying concentration (0.1, 0.3, and 0.5 wt.% based on resin weight). Studying the cure kinetics and thermal stability of these nanocomposites would pave the way toward the design of high-performance nanocomposites for special applications. Scanning electron microscopy (SEM) and transmittance electron microscopy (TEM) revealed AlPO2 particles having domains less than 60 nm with high potential for agglomeration. Excellent (at heating rate of 5 °C/min) and Good (at heating rates of 10, 15 and 20 °C/min) cure states were detected for nanocomposites under nonisothermal differential scanning calorimetry (DSC). While the dimensionless curing temperature interval (ΔT*) was almost equal for epoxy/AlPO2 nanocomposites, dimensionless heat release (ΔH*) changed by densification of polymeric network. Quantitative cure analysis based on isoconversional Friedman and Kissinger methods gave rise to the kinetic parameters such as activation energy and the order of reaction as well as frequency factor. Variation of glass transition temperature (Tg) was monitored to explain the molecular interaction in the system, where Tg increased from 73.2 °C for neat epoxy to just 79.5 °C for the system containing 0.1 wt.% AlPO2. Moreover, thermogravimetric analysis (TGA) showed that nanocomposites were thermally stable.