Transition Temperature Research Articles

Regioselective Copolymerization of Glucose-Derived Allopyranoside Epoxide with Cyclic Anhydrides: Developing Precise Sugar-Functionalized Polyesters with Unique Altrose Linkages.

Uniform sugar-functionalized polyesters combine the benefits of sugar's structural diversity, biocompatibility, and biodegradability with precise postfunctionalization capabilities, making them a highly valuable class of materials with extensive application potential. However, the irregular placement of hydroxyl groups has limited the synthesis of these polyesters. Here, we present the first platform for uniform sugar-functionalized polyesters via regioselective ring-opening copolymerizations (ROCOPs) of allopyranoside anhydrosugar epoxide (1, derived from d-glucose) with cyclic anhydrides, followed by complete selective deprotection. This method yields polyesters with controlled molecular weights, narrow molecular weight distributions (D̵ < 1.19), high glass transition temperatures (up to 188 °C), and uniform hydroxyl functionality. Furthermore, the degradation of the polyesters offers an efficient route for producing the highly valuable d-altrose. Mechanistic insights, supported by DFT calculations, as well as NMR and HPLC analyses, confirm the regioselective nucleophilic attack at the C2 position of the pyranose ring. Kinetic studies reveal a first-order dependence on 1 and a zero-order dependence on the cyclic anhydrides. Additionally, these uniform sugar-functionalized polyesters can be incorporated into triblock terpolymers through one-pot/one-step or one-pot/two-step procedures, forming uniform sugar-functionalized multiblock copolymers.

Influence of irradiation temperature on REBCO tape degradation

Abstract Commercial Rare Earth Barium Copper Oxide (REBCO) coated conductor tapes were irradiated at temperatures ranging from 20 K to 300 K with 1.2 MeV protons up to fluences of 1021 m-2. With in situ transport current measurements, we found that self-field critical currents (Ic) and transition temperature (Tc ) degrade in cold (20-200 K) irradiations by a factor of 1.6 faster than in 300 K irradiations. This warrants caution when basing the development of REBCO fusion magnets, which are operated at 20 K, on results from room-temperature irradiations. The degradation of Ic , n-value and Tc for irradiations in the range 20-200 K closely matched each other. However, small annealing effects can already be observed at 80 K, which is a lower threshold than previously thought. The observed Ic recovery increases with annealing temperature and is at 300 K four times higher than at 200 K. And finally, we compared the experimental data from this study with the calculated decrease of superfluid density, and find a surprisingly good correlation, supporting the Eisterer hypothesis for Ic degradation.

Microstructural insights into the coarse-grained heat-affected zone of a high-strength all-weld metal: Development of a continuous cooling transformation diagram

AbstractThe present study deals with the development of a continuous cooling transformation diagram corresponding to the coarse-grained heat-affected zone of a high-strength all-weld metal with a minimum yield strength of 1100 MPa fabricated via gas metal arc welding. Dilatometry tests were conducted to determine the transition temperatures. High-resolution imaging methods, such as transmission electron microscopy and atom probe tomography, as well as nanoindentation, were employed to resolve the microstructural constituents. At fast cooling rates (t8/5 from 1.4 to 25 s), the microstructure comprises a mixture of martensite and coalesced bainite, with a slight increase in the content of coalesced bainite with faster cooling. This demonstrates that coalesced bainite cannot be avoided in the coarse-grained heat-affected zone of the current alloy by increasing the cooling rate. With slower cooling (t8/5 ≥ 50 s), the microstructure becomes increasingly bainitic, accompanied by a marginal drop in Vickers hardness. At t8/5 times of 500 s and 1000 s, the all-weld metal consists of granular bainite with significant amounts of retained austenite and different shaped martensite-austenite constituents. The coarser massive-type constituents contain body-centered cubic grains, sized in the hundreds of nanometers, with a hardness approximately twice as high as that of the surrounding bainitic matrix.

Studies on Synthesis, Physical and Optical Properties of Dysprosium Ion-Doped Transparent Heavy Metal Oxide Glasses

The melt quench method was used to synthesize Dysprosium ions doped heavy metal oxide glasses of composition 50%TeO2–(30-x)%B2O3-10%Bi2O3–10%Na2O–x%Dy2O3(mol%) (x= 0, 0.2, 0.4, 0.6 and 0.8). The proof of glassy nature of prepared samples is substantiated by the X-ray diffractogram (XRD). Differential scanning calorimetry (DSC) is carried to obtain the value of glass transition temperature (Tg). Physical parameters such as polaron radius, density, inter-ions distance, lanthanide ion concentration and oxygen packing density (OPD) were calculated. Tauc’s plot is drawn to get information of energy band gap and hence refractive index. The distinctive absorption bands of dysprosium ions exist at 320, 348, 365, 387, 794, and 882 nm. The energy transitions from the 6H15/2 level to various higher levels of dysprosium ions are responsible for the UV-VIS-NIR absorption spectra. Using emissions monitoring at 576 nm, the excitation spectra was obtained between 200 and 550 nm. The 6H15/2→4I13/2, 4G11/2, 4I15/2, and 4F9/2 transitions were identified as the sources of the excitation bands at 390, 426, 452 and 470 nm, respectively. Notable bands of emission were observed when stimulated at 447 nm for 485, 575, 662, and 756 nm wavelengths it is due to the energy transfer from 4F9/2→6H15/2, 4F9/2→6H13/2, 4F9/2→6H11/2, and 4F9/2→6H9/2, 6F11/2. It was found the light emission from the samples was white.

Manipulating ambient pressure superconductivity in metal borocarbides through hole doping.

A Ca2B4C4 ternary compound obtained by using a machine learning (ML) guided structure search is found to be metastable with a formation energy of only 18 meV/atom above the convex hull but exhibits only marginal superconducting transition temperature (Tcc). By replacing Ca with Na, the electronic density of states (DOS) at the Fermi level is significantly enhanced, increasing the predicted Tc to 21.9 K. Extending this hole-doping strategy to other Ca-B-C compounds, we found that while Na4B2C22 remains superconducting with a Tc of 4.0 K, Na substitution in Ca2B4C8 transforms it from a semiconductor to a superconductor with a Tc of 28.9 K. The flat σ bands, particularly from the 2px and 2py orbitals of carbon, and a Van Hove singularity at the Fermi level, play crucial roles in enhancing the superconductivity. This work introduces a new class of B-C-based superconductors and broadens the compositional space for high-temperature superconducting materials.&#xD.

Thickness effect on the evolution of superconducting properties in FeSe0.4Te0.6 thin films.

Abstract A series of high-quality FeSe0.4Te0.6 epitaxial thin films with different thicknesses were fabricated on CaF2 substrates by pulsed laser deposition. With increasing the film thickness, the superconducting transition temperature is enhanced rapidly but deteriorates gradually in over thick films. The superconducting transition occurs in all films including the 5 nm one, and Tc above 21 K persists in the films with thicknesses from 45 to 180 nm. We find that Tc and the c-axis lattice constant show a nearly linear correlation, suggesting a strong interdependence between Tc and the lattice strain characteristics. The upper critical field, anisotropy and effective pinning energy are studied in detail for the 15, 60, 90 and 180 nm films. These observations provide key insights in understanding the thickness effect on the superconductivity of the FeSe0.4Te0.6 films.

A high-temperature multiferroic Tb2(MoO4)3

Magnetoelectric mutual control in multiferroics, which is the electric control of magnetization, or reciprocally the magnetic control of polarization has attracted much attention because of its possible applications to spintronic devices, multi-bit memories, and so on. While the required working temperature for the practical application is much higher than room temperature, which ensures stable functionality at room temperature, the reported working temperatures were at most around room temperature. Here, we demonstrated magnetic control of ferroelectric polarization at 432 K in ferroelectric and ferroelastic Tb2(MoO4)3, in which the polarity of ferroelectric polarization is coupled to the orthorhombic strain below the transition temperature 432 K. The paramagnetic but strongly magnetoelastic Tb3+ magnetic moments enable the magnetic control of ferroelectric and ferroelastic domains; the ferroelectric polarization is controlled depending on whether the magnetic field is applied along [110] or [11¯0]. This result may pave a new avenue for designing high-temperature multiferroics.

Crystallization of n-Alkanes under Anisotropic Nanoconfinement in Lipid Bilayers.

Understanding crystallization behavior is integral to the design of pharmaceutical compounds for which the pharmacological properties depend on the crystal forms achieved. Very often, these crystals are based on hydrophobic molecules. One method for delivering crystal-forming hydrophobic drugs is by means of lipid nanoparticle carriers. However, so far, a characterization of the potential crystallization of fully hydrophobic molecules in a lipid environment has never been reported. In this work we investigate the crystallization behavior of two model hydrophobic chains, n-eicosane (C20) and n-triacontane (C30), in phospholipid bilayers. We combine static 2H nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry (DSC) and show that C30 molecules can indeed crystallize inside DMPC and POPC bilayers. The phase transition temperatures of C30 are slightly reduced inside DMPC, and rotator phase formation becomes a two-step process: Preorganized n-alkane chains assemble in rotator-phase crystallites just as fast as bulk C30, but further addition of molecules is notably slower. Under the same isothermal conditions, different crystal forms can be obtained by crystallization in the membrane and in bulk. In excess water conditions, homogeneous nucleation of C30 is observed. The initial anisotropic molecular arrangement of C30 molecules in the membrane is readily recovered upon reheating, showing reversibility. The shorter C20 molecules on the other hand become trapped in the DMPC membrane gel-phase upon cooling and do not crystallize. This work marks the first observation of the crystallization of hydrophobic chains inside a lipid bilayer environment. As such, it defines a fundamental starting point for studying the crystallization characteristics of various hydrophobic molecules in lipid membranes.

Low‐Temperature Cured and High‐Toughness Epoxy Resin Modified by Triblock Liquid Rubber

ABSTRACTLow‐temperature cured epoxy resin (EP) is a suitable resin system for bonding thermal and temperature‐sensitive devices, which can also reduce energy consumption and production costs. In order to further broaden the application range of low‐temperature curing EP systems in amine‐sensitive environments, in addition to selecting a well‐compatible curing agent, an effective rubber to form a three‐dimensional network structure with the resin matrix, so as to significantly improve the toughness of the EP. In this work, two kinds of triblock liquid rubber hydroxy‐terminated polypropylene glycol‐polybutadiene‐polypropylene glycol (HTPO‐PB‐PO) and hydroxy‐terminated polyphenylethylene oxide‐polybutadiene‐polyphenylethylene oxide (HTSO‐PB‐SO) with controlled molecular weight are synthesized and adopted to improve the mechanical properties of cured EP with methyl hexahydro phthalic anhydride (MEHHPA). It is found that all triblock liquid rubber‐modified epoxy systems can be cured below 100°C, and the curing mechanism is similar to that of the pure EP system. Compared with the original pure EP, the impact resistance of modified samples is significantly improved, and the glass transition temperature (Tg) is similar, among which the best impact strength of modified EP can reach 16.22 kJ/m2, 62.7% higher than that of the pure sample with only slightly reduced thermal decomposition temperature. These results can provide a low‐temperature curing resin material with excellent mechanical properties, high dimensional accuracy, and high heat resistance for amine‐sensitive environments while reducing costs due to high‐temperature components and energy consumption.

Predicting the glass transition temperature of polymer based on generative adversarial networks and automated machine learning

AbstractSolution styrene‐butadiene rubber (SSBR) finds wide applications in high performance tire design and various other fields. This study aims to create a quantitative structure–property relationship (QSPR) model linking SSBR's glass transition temperature (Tg) to its structural properties. A dataset of 68 sets of data from published literature was compiled to develop a predictive machine learning model for SSBR's structural design and synthesis using small sample sizes. To tackle small sample sizes, a framework combining generative adversarial networks (GAN) and the Tree‐based Pipeline Optimization Tool (TPOT) is proposed. GAN is first used to generate additional samples that mirror the original dataset's distribution, expanding the dataset. The TPOT is then applied to automatically find the best model and parameter combinations, creating an optimal predictive model for the mixed dataset. Experimental results show that using GAN to enlarge the dataset and TPOT regression models significantly enhances model performance, increasing the R2 value from 0.745 to 0.985 and decreasing the RMSE from 7.676 to 1.569. The proposed GAN–TPOT framework demonstrates the potential of combining generative models with automated machine learning to improve materials science research. This combination accelerates research and development processes, enhances prediction and design accuracy, and introduces new perspectives and possibilities for the field.

A Two-Dimensional Superconducting Electron Gas at LaFeO3/SrTiO3 Interfaces.

Transition metal oxide interfaces have garnered great attention due to their fascinating properties that are absent in their bulk counterparts. The high mobility and coexistence of superconductivity and magnetism at these interfaces remain compelling research topics. Here, we first report superconductivity in the 2DEG formed at the LaFeO3/SrTiO3 interfaces, characterized by a superconducting transition temperature (Tc) of 333 mK and a superconducting layer thickness of 13.7 nm. The observation of a Berezinskii-Kosterlitz-Thouless transition at low temperatures indicates the two-dimensional nature of the superconductivity. Such two-dimensional superconductivity can be tuned by applying a gate voltage (Vg) across the SrTiO3 substrate, showing a dome-shaped Tc-Vg dependence. Moreover, we observe a hysteretic behavior in the magnetoresistance in the superconducting regime, and the underlying mechanism requires further investigation. Our results unveil the superconducting characteristics of 2DEG at LaFeO3/SrTiO3 interfaces and offer a new compelling platform to investigate emergent quantum phenomena at oxide interfaces.

Transient Thermal Mapping Utilizing the Sintering of Glass‐Ceramics

Thermal paints are essential for mapping the surface temperature of gas turbine engine components but can only indicate maximum temperature. A novel transient thermal history sensor that combines the capabilities of a thermocouple with those of a thermal paint is developed here, enabling the retrieval of full thermal history using a “sintering” model. The glassy ceramic thermal paint undergoes a qualitative optical transition due to sintering in response to temperature that is quantified using UV–vis spectroscopy. This provides high‐resolution transient temperature measurement (±6 °C) when maximum temperature is above its glass transition temperature (Tg) of 563 °C and up to 660 °C. The glass‐ceramic coating exhibits strong adhesion to Inconel 718 substrates due to matched coefficients of thermal expansion. By fabricating similar paints with distinct temperature ranges and placing them in proximity, this approach can significantly reduce the number of thermocouples needed for surface temperature mapping, thereby improving the accuracy of measurements required for engine validation.

Connecting Dynamics and Thermodynamics in Polymer–Resin Cured Systems

This work connects the calorimetric responses of different rubber–resin blends with varying resin contents with their alpha relaxation dynamics. We used differential scanning calorimetry and broadband dielectric spectroscopy to characterize the calorimetric and dielectric responses of styrene–butadiene, polybutadiene, and polyisoprene with different resin contents. To model the results, we used the Gordon–Taylor equation combined with an extension of the Adam–Gibbs approach. Thus, we propose a simple and effective model that allows us to estimate the blend dynamics from the temperature dependence of the relaxation times of the pure components and the calorimetric measurement of the glass transition temperature of only one blend composition. By estimating an effective interaction parameter from calorimetry, we achieved accurate alpha relaxation dynamics predictions for different resin concentrations. Our highly predictive approach provides a realistic description of the expected dynamics. This study offers valuable insights into the dynamic properties of polymer compounds, paving the way for the fast and effective development of advanced and more sustainable materials.

Experimental and Theoretical Evidence of Weak Spin–Lattice Coupling in the Double Perovskite Sr2YRuO6

ABSTRACTSr2YRuO6 is a material that provides an ideal platform for studying magnetic frustration in three‐dimensional geometries. Herein, we combine Raman spectroscopy and density functional theory calculations to establish connections between the lattice dynamics and magnetic states in Sr2YRuO6 single crystals. The x‐ray diffraction profiles reveal that Sr2YRuO6 possesses an ordered double‐perovskite structure with distorted monoclinic symmetry. Three magnetic phase transitions are observed and linked to the presence of weak ferromagnetism at 135 K and short‐ and long‐range antiferromagnetic orderings at 32 and 26 K. The oxygen‐octahedron antistretching and stretching modes, observed at 570 and 766 cm−1, exhibit anomalies near the magnetic phase transition temperatures, indicating an intriguing interplay between the lattice and spin degrees of freedom. Their spin–phonon coupling constants of 0.7 cm−1 reflect the weak spin–lattice interactions in Sr2YRuO6.

Dynamically Switchable Multifunctional Device for Terahertz Application using Vanadium Dioxide and Graphene-Based Metasurface

Abstract In this article, a dynamically switchable and multifunctional metasurface is realized using a combination of vanadium dioxide (VO2) and graphene-based structures. The device can be tuned using the temperature transition property of vanadium dioxide from a wideband linear-to-circular polarization converter (LTCPC) to a wideband linear-to-linear cross polarization converter (LTLPC) and a dual-band absorber. The unit cell is designed with a gold-backed lossy-silicon dioxide (SiO2) substrate with a permittivity of 3.9, and the top metasurface layer is designed with a graphene-based dual triangle loaded split ring (DTLSR) and two stripes of vanadium oxide to cover the split partially. The proposed device can be used as a wideband LTCPC at normal temperature (298 K) from 1.43 THz to 2.85 THz, i.e., 66.35% fractional bandwidth (FBW). At temperatures greater than 341 K, VO2 exhibits metallic properties, and the structure functions as LTLPC from 1.82 THz to 3.31 THz (PCR ≥ 80%), i.e., 58.08 % FBW and maximum polarization conversion ratio (PCR) reported as high as 99.65 %. Furthermore, at this metallic condition, two absorption peaks are obtained at 1.22 THz and 3.30 THz with absorptivity of 93.5% and 100%, respectively. The device offers incident angle invariability up to 40° for LTCPC and up to 50° for LTLPC operation. Further insight into the mechanism of operation is developed using the surface current density and electric field distribution analysis. The advantage of the proposed metasurface over other similar structures is assessed with respect to multifunctional behavior, bandwidth, and stability under oblique incidence.&amp;#xD;

Study on Preparation, Structure, and Properties of Flexible Shape Memory Epoxy Resin

To improve the toughness of epoxy resins, we add N, N-dimethylformamide (DMF) to epoxy resin as it is curing, and the flexible epoxy resin is prepared. According to the results of Fourier Transform Infrared Spectroscopy (FT-IR), DMF is able to effectively graft onto the epoxy resin. The glass transition temperature (Tg) of the epoxy resin drops from 99.9°C to 19.4°C, indicating a reduction in the thermodynamic stability of DMF/epoxy, according to the results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). According to tensile studies, DMF/epoxy's mechanical strength is decreased, but its elongation is significantly longer and enhanced by three orders of magnitude. Impact testing reveals a significant improvement in the material's hardness (from 1.67 to 15 J·cm-2). Furthermore, DMF/epoxy is flexibly bendable. Finally, the DMA test shows that DMF/epoxy can achieve good shape memory at low temperatures to room temperature.

Dynamic Mechanical Properties of Elastomeric Poly(n‐Butyl Acrylate) Ionomers

ABSTRACTThis research explored the impact of temperature on the mechanical properties of poly(n‐butyl acrylate‐co‐Na methacrylate) (PBA) ionomers, as an elastomeric ionomer, with an emphasis on their ion content. The PBA ionomers were found to exhibit dual glass transition temperatures (Tgs) and ionic plateaus, characteristics typically observed in other amorphous ionomers. Significantly, in PBA ionomers, ionic aggregates (i.e., multiplets) functioned like chemical cross‐linking points in addition to their conventional role as physical cross‐links. This dual functionality resulted in an upward shift of the rubbery plateau and a consequent enhancement of storage moduli. In a comparative analysis of the mechanical properties of PBA, poly(ethyl acrylate) (PEA), and poly(styrene‐methacrylate) (PSMA) ionomers, it was determined that the extent of ionomer clustering increased progressively from PBA ionomer to PEA ionomer to PSMA ionomer. The mechanical properties of these three ionomer systems were interpreted through the lens of multiplet formation mechanisms, with a particular focus on the quantity of multiplets and the number of ion pairs per multiplet, both of which were modulated by the matrix Tgs of each ionomer.

Mechanically robust and thermal stable polyurethane elastomers with self‐healing and recycling ability

AbstractA series of supramolecular interaction‐based polyurethane elastomers (SPUEs) were synthesized from the reactions of hexamethylene diisocyanate‐functionalized 2‐ureido‐4[1H]‐pyrimidinone (UPy) derivatives and polytetrahydrofuran (PTHF), followed by reactions with polyether amines. The tensile strength, elongation at break and toughness of the optimum SPUE system can reach 62 MPa, 693%, and 189 MJ·m−3, respectively. All SPUEs have much higher tensile strength and toughness than the reference materials while maintaining large elongation at break owing to the increased hydrogen (H)‐bonding sites and favorable crosslinked networks. SPUEs possess double glass transition temperatures and display good multi‐shape memory behaviors resulting from different soft and hard domains. SPUEs have nanophase‐separated structures, which endow them with excellent transparency within visible light wavelengths ranging from 500 to 800 nm. Owing to adequate H‐bonds, SPUEs exhibit stress relaxation, shape‐reconfigurability, and outstanding healing/recycling properties. The damaged SPUEs show high healing efficiency of 77–97% after heat treatment at 100°C for 12 h. The used SPUEs can be recycled multiple times by dissolving them in N, N‐dimethylformamide (DMF) at ~110°C for 20–30 min, and the third recycled SPUEs can have high mechanical strength retention rate of up to 100%.Highlights Elastomer was constructed through H‐bonds and favorable crosslinked networks. The elastomer has high comprehensive mechanical properties. The elastomer has extremely low and high glass transition temperatures. The elastomer has a high self‐healing efficiency of ~97% after treatment at 100°C. The elastomer can be recycled multiple times.

Effect of Soft Segment Structures on the Properties of Self‐Healing Photopolymerizable Thiocarbamate‐Based Polyurethanes

ABSTRACTThree self‐healing photopolymerizable thiocarbamate‐based polyurethane oligomers were synthesized using different macromolecular chain extenders: polypropylene glycol (PPG‐1000), polytetrahydrofuran (PTMG‐1000), and polycaprolactone glycol (PCL‐1000). The variations in the soft segment structures had minimal impact on the double bond conversion and gel fraction of the light‐cured self‐healing thiocarbamate‐based polyurethane materials, achieving double bond conversion rates and gel fractions exceeding 87%. Incorporating polycaprolactone diol as the soft segment improved heat resistance and tensile stress but reduced the material's self‐healing ability. Conversely, utilizing polytetrahydrofuran as the soft segment resulted in outstanding overall performance, notably lowering the glass transition temperature to −48.4°C, increasing tensile strain to 1280%, achieving a self‐healing efficiency of up to 90%, and exhibiting good degradation properties.

Dynamic and thermodynamic behavior of supercooled Na–Ba metaphosphate liquids: Role of modifier cation ordering

AbstractThe Q‐speciation and the role of modifier dynamics on network relaxation in the supercooled mixed‐alkali–alkaline‐earth (MAAE) Na–Ba metaphosphate liquids are investigated using a combination of 31P nuclear magnetic resonance (NMR) spectroscopy, calorimetric, electrical conductivity, and rheological measurements. Progressive replacement of Na with Ba in these glasses is shown to result in an increasing disproportionation of Q2 species via the reaction: 2Q2 = Q1 + Q3. Unlike mixed‐alkali liquids, the Na–Ba metaphosphate liquids display a monotonic variation in isothermal electrical conductivity, glass transition temperature, calorimetric and kinetic fragility, and isothermal viscosity. It is hypothesized that this monotonic variation arises from the lack of elastic facilitation of network relaxation via coupled hopping of Na–Ba pairs as these modifier cations are prohibited from mixing randomly due to the differences between their size, mass, charge, and mobility. Isobaric heat capacity measurements provide supporting evidence in favor of a such a nonrandom mixing between the modifier cations in Na–Ba metaphosphate glasses and liquids.