Transition Temperature Research Articles

Computation Legendre moments using image analysis technique

Abstract In this paper, phase transition temperatures of nematic liquid crystals: 4-n alkoxy benzoic acid (nOBA, where n = 4 and 6) are determined from the Legendre moments of liquid crystal textures. Here, the image analysis technique in conjunction with polarizing optical microscope is used to compute the Legendre moments from the textures of liquid crystals. As a function of temperature, Liquid crystal textures are recorded from the arthroscopic mode of optical microscope. Changes in textural features of the sample with respect to temperature bring the variations in intensity values of liquid crystal textures. The brightness image that is generated from the liquid crystal textural patterns separates the information about fluctuations in intensity. In this approach, Legendre moments are computed from the brightness images of the liquid crystal textures and are plotted as a function of temperature. Significant variations in the brightness Legendre moment curve provide insight into the liquid crystal transition temperatures. Results obtained from the present methodology are compared with gray color textures data and the experimental technique of differential scanning calorimetry and are in good agreement with each other. This method is an objective and quantitative technique whereas POM method is qualitative and subjective.

Spin Transport Modulation of 2D Fe3O4 Nanosheets Driven by Verwey Phase Transition.

Realizing spin transport between heavy metal and two-dimensional(2D) magnetic materials at high Curie temperature (TC) is crucial to advanced spintronic information storage technology. Here, environmentally stable 2D nonlayered Fe3O4 nanosheets are successfully synthesized using a reproducible process and found that they exhibit vortex magnetic domains at room temperature. A Verwey phase transition temperature (TV) of ≈110 K is identified for ≈3nm thick nanosheet through Raman characterization and spin Hall device measurement of the Pt/Fe3O4 bilayer. The anisotropic magnetoresistance ratio decreases near TV, while both the spin Hall magnetoresistance ratio and spin mixing conductance (Gr) increase at TV. As the temperature approaches 112 K, the anomalous Hall effect ratio tends to become zero. The maximum Gr reaches ≈5 × 1015 Ω-1m-2 due to the clean and flat interface between Pt and 2D nanosheet. The observed spin transport behavior in Pt/Fe3O4 spin Hall devices indicates that 2D Fe3O4 nanosheets possess potential for high-power micro spintronic storage devices applications.

MDI-PTMG-based TPU modified asphalt: Preparation, rheological properties and molecular dynamics simulation

Thermoplastic polyurethane elastomer (TPU) modified asphalt was prepared by a two-step process using MDI and PTMG. The improvement effects of different TPU content on high-and low-temperature rheological properties and thermal stability of asphalt were studied through experimental tests. The results showed that TPU could enhance the high-temperature properties of asphalt obviously. The improvement effect was more significant with the increase of TPU content. At the same time, glass transition temperature (Tg) of asphalt decreased with the increase of TPU content, indicating that TPU could improve the low-temperature performance of asphalt. These experimental results were further verified by the Molecular dynamics (MD) simulation results. Materials Studio 8.0 was used to establish the molecular models of asphalt, TPU and TPU modified asphalt. The effects of TPU content on mechanical modulus and Tg of asphalt were studied by MD simulation. The results revealed that TPU formed a close structure with asphalt to improve the structural stability of asphalt. And the free volume fraction of the modified asphalt decreased with the increase of TPU content. Thus, the high-temperature properties of asphalt were improved. The calculated Tg and moduli obtained from MD simulation accorded well with the experimental results from DSC and DSR, respectively. This study suggests a novel way to provide guidance for the development of TPU modified asphalt.

Molecular investigation on physical and tensile properties of polyethylene (PE) under high-pressure hydrogen environments

Polymer liners are key components of high-pressure hydrogen storage tanks, and understanding their behaviour under such environments is crucial for safety. This study employs molecular dynamics (MD) simulation to investigate the physical and tensile properties of amorphous polyethylene (PE) under the effects of hydrogen content, pressure, temperature. It is found that hydrogen molecules decrease glass transition temperature by approximately 3%, while pressure have no noticeable impact. Meanwhile, hydrogen molecules enhance diffusivity, while pressure suppresses diffusivity and exhibits a more pronounced impact, resulting in an overall decrease of 44% in diffusivity under high-pressure hydrogen. Tensile stress also increases the diffusivity by 17%. Hydrogen molecules weaken the non-bonded molecular interactions of PE, which reduces the percentage of trans conformation and orientation parameters. Meanwhile, hydrogen also suppresses the internal energy change of PE induced by tensile deformation. Therefore, hydrogen molecules lead to a decrease in tensile properties. Comparatively, pressure causes PE to produce more trans conformations under tension, which improves orientation, entanglement parameters, and the internal energy change of PE, and finally enhances the tensile properties of PE. The effect of pressure surpasses that of hydrogen, which results in an approximately 40% increase in tensile properties under high-pressure hydrogen. This study provides molecular-level insights into the individual and coupled effects of hydrogen and pressure, forming a foundation for predicting polymer behaviour under high-pressure hydrogen conditions.

Reduction of pseudocritical temperatures of chiral restoration and deconfinement phase transitions in a magnetized PNJL model

We investigate the chiral restoration and deconfinement phase transitions under an external magnetic field in the frame of a Pauli-Villars regularized Polyakov loop extended Nambu-Jona-Lasinio model. A running Polyakov loop scale parameter T0(eB) is introduced to mimic the reaction of the gluon sector to the presence of magnetic fields. It is found that a decreasing T0(eB) with magnetic fields can realize the inverse magnetic catalysis phenomena of chiral condensates of u and d quarks, increase of Polyakov loop, and the reduction of pseudocritical temperatures of chiral restoration and deconfinement phase transitions. Published by the American Physical Society 2024

Warm white light emitting thermally stable Dy3+ activated antimony fluoroborate glasses for n-UV based white LEDs

A transparent series of trivalent dysprosium (Dy3+) ions activated calcium antimony fluoroborate glass samples (CAFB) were synthesized by the aid of the melt quenching process. The thermogravimetric, structural, and spectroscopic characterizations were evaluated and investigated in detail. Thermogravimetric analysis was performed to determine the glass transition temperature Tg and crystallization temperature (Tc) of the prepared host CAFB glass. Raman Spectroscopy and Fourier transform infrared (FT-IR) analyzed the structural orientation as well as bonding formation in the prepared CAFB host and CAFBDy1.0 glass matrix. Furthermore, the optical absorption spectra exhibit various absorption peaks between the n-UV to NIR region (350 to 2000 nm). Under the different n-UV excitation wavelengths, photoluminescence (PL) spectra reflect three foremost emission centres located around 482, 575, and 663 nm in the Dy3+: CAFB glasses. The observed colour coordinates of the prepared CAFBDy glasses were marked in the standard white area of the CIE chart under different n-UV excitation wavelengths. Moreover, temperature-dependent PL (TDPL) studies demonstrate that these glass samples have significant thermal stability and also a large activation energy. Hence, the above-mentioned results prove the versatility of the CAFBDy glasses to make them potential candidates for usage in luminescent device applications.

Free Volume Mediated Decoupling of Ionic Conduction from Segmental Relaxation Leading to Enhancement in Ionic Conductivity of Polymer Electrolytes at Low Temperatures.

Coupling between segmental relaxation and ionic conduction has limited the ionic conductivity of flexible polymers like poly(ethylene oxide), PEO, based electrolytes especially at low temperatures where segmental relaxation becomes extremely slow. In the present study, we show that ionic conduction becomes decoupled from segmental relaxation in PEO-based electrolytes simply by loading succinonitrile (SN). As a result of SN interactions induced rigid chain packing of PEO, the semicrystalline morphology of PEO is completely altered along with the enhancement in number density of free volumes having smaller size and narrower size distribution. These free volumes provide additional pathways for ionic diffusion independent of segmental relaxations of PEO leading to decoupling of ionic diffusion from the segmental relaxation process. The decoupling finally leads to nearly two orders higher ionic conductivity (∼10-11 Scm-1)at glass transition temperature (Tg ∼ 210 K), than what is expected in the case of complete coupling.

Highly Sensitive Two‐Dimensional Ruddlesden‐Popper Perovskites for Thermochromic Smart Windows

AbstractWith the growing demand for high‐performance smart windows, the discover of a class of thermochromic materials with reversible cycling and rapid response characteristics has become urgent. In this work, we have uncovered a two‐dimensional (2D) Ruddlesden‐Popper (RP) phase halide perovskite, (PMA)2MAPb2I7−xClx, where PMA=C6H5CH2NH3 and MA=CH3NH3, exhibiting exceptional reversible thermochromic properties. The 2D RP phase perovskite thin film features a low transition temperature (Tc=30 °C from the hydrated state to the hot state, along with a fast transition time of 40 s. Furthermore, the addition of 0.5 times excess MAI significantly enhances the visible light transmittance of the hydrated state. Characteristic hydration peaks in X‐ray diffraction patterns and O−H bond absorption peaks Fourier‐transform infrared spectra are observed in the thin film in its hydrated state, which disappear in the hot state, validating its reversible thermochromic properties. Additionally, a solar cell based on the thermochromic 2D RP phase thin film achieves a power conversion efficiency of 2.31 %, offering a promising solution for advanced smart window technologies.

Responsibility of small defects for the low radiation tolerance of coated conductors

Abstract Rare-earth-barium-copper-oxide based coated conductors exhibit a relatively low radiation robustness compared to e.g. Nb3Sn due to the d-wave symmetry of the order parameter, rendering impurity scattering pair breaking. The type and size of the introduced defects influence the degrading effects on the superconducting properties; thus the disorder cannot be quantified by the number of displaced atoms alone. In order to develop degradation mitigation strategies for radiation intense environments, it is relevant to distinguish between detrimental and beneficial defect structures. Gadolinium-barium-copper-oxide based samples irradiated with the full TRIGA Mark II fission reactor spectrum accumulate a high density of point-like defects and small clusters due to n - γ capture reactions of gadolinium. This leads to a 14–15 times stronger degradation of the critical temperature compared to samples shielded from slow neutrons. At the same time both irradiation techniques lead to the same degradation behavior of the critical current density as function of the transition temperature J c ( T c ) . Furthermore, annealing the degraded samples displayed the same T c recovery rates, indicating the universality of the defects responsible for the degradation. Since the primary knock on atom of the n - γ reaction as well as the recoil energy is known, we used molecular dynamics simulations to calculate which defects are formed in the neutron capture process and density functional theory to assess their influence on the local density of states. The defects found in the simulation were mainly single defects as well as clusters consisting of Oxygen Frenkel pairs, however, more complex defects such as Gd C u antisites occurred as well.

From weak to strong-coupling superconductivity tuned by substrate in TiN films

Abstract The interplay between substrates and superconducting thin films has attracted increasing attention. Here, we report an in-depth investigation on superconducting properties of the epitaxial TiN thin films grown on three different substrates by dc reactive magnetron sputtering. The TiN films grown on (0001) sapphire exhibit (111) crystal orientation, while that grown on (100) Si and MgO substrates exhibit (100) orientation. Moreover, the samples grown on Si reveal a relatively lower level of disorder, accompanied by the higher critical transition temperature Tc and smaller magnitude of upper critical field slope near Tc. Remarkably, we uncovered a rather high value of superconducting gap (with Δ0/kBTc = 3.05) in TiN film on Si indicating a very strong coupling superconductivity, in sharp contrast to the case using sapphires and MgO as the substrate which reveals a weak-coupling feature. The comprehensive analysis considering the scenarios of the three substrate shows that the grain size of the thin films may be an important factor influencing the superconductivity.

Kagome materials AV3Sb5 (A=K,Rb,Cs): pairing symmetry and pressure-tuning studies

Abstract The vanadium-based kagome metals AV3Sb5 (A = K, Rb, and Cs) host a superconducting ground state that coexists with an unconventional charge density wave (CDW). The CDW state exhibits experimental signatures of chirality, electronic nematicity, and time-reversal-symmetry breaking, raising the questions whether the superconductivity (SC) in AV3Sb5 may also be unconventional, how SC interplays with CDW, and how the two orders evolve upon tuning. This article reviews studies of the superconducting pairing symmetry, and the tuning of SC and CDW in the AV3Sb5 compounds. Various experimental techniques consistently find that CsV3Sb5 exhibits nodeless SC, which remains robust regardless whether the CDW is present. Under hydrostatic pressure, SC in AV3Sb5 becomes enhanced as the CDW is gradually suppressed, revealing a competition between the two orders. In CsV3Sb5, a new CDW state emerges under pressure that competes more strongly with SC relative to the CDW at ambient pressure, and results in two superconducting domes that coexist with CDW. After the CDW in AV3Sb5 is fully suppressed with hydrostatic pressure, a further increase in pressure leads to a nonmonotonic evolution of the superconducting transition temperature driven by lattice modulations. Thickness is shown to be a powerful tuning parameter in AV3Sb5 thin flakes, revealing the evolution of CDW and SC upon dimensional reduction, and can be combined with hydrostatic pressure to shed light on the interplay between SC and CDW. Based on results reviewed in this article, we discuss outstanding issues to be addressed in the AV3Sb5 systems.

Copolymerization of novel self-promoted curing phthalonitrile with epoxy resin and its thermal property

The disadvantage of poor thermal performance of epoxy resin limits its application in special fields, therefore we improve the thermal performance of epoxy resin by copolymerizing it with phthalonitrile resin. A novel self-promoted curing phthalonitrile monomer containing pyridine rings and amino groups (APNH) was successfully synthesized using 2-amino-4-hydroxypyridine and 4-nitrophthalonitril, and characterized by FTIR and NMR spectra. DSC confirmed that the APNH monomer exhibits curing behavior that is self-promoting. Copolymerizing the APNH monomer with epoxy resin enhances the thermal performance of the epoxy resin. The curing behavior of the EPNH copolymer was studied using DSC, which revealed two distinct curing peaks. FTIR analysis showed that the EPNH copolymer has formed structures such as triazine, phthalocyanine, and isoindoline. The presence of cyano groups significantly enhances the thermal properties of the copolymer, surpassing those of traditional epoxy resins. This enhancement in thermal performance amplifies with an increase in the content of the APNH monomer. The research indicates that the EPNH copolymer exhibits superior thermal stability and elevated glass transition temperatures, facilitating the application of epoxy resin in specialized areas.

Development of a novel approach to correlate small punch fatigue with uniaxial ratcheting fatigue

The miniaturization of fatigue specimens has seen significant advancements, realized either by scaling down conventional specimens while preserving their geometry or by experimenting with novel specimen shapes and loading configurations. In this study, the small punch test (SPT) technique, which is well-established for estimating tensile, creep, and ductile-to-brittle transition temperature (DBTT), is employed to predict the cyclic deformation behaviour of SS 316LN and modified 9Cr-1Mo (P91) steels. The small punch fatigue (SPF) experiments demonstrated continuous displacement accumulation, similar to strain accumulation in ratcheting. The study evaluates the influence of various load parameters, such as amplitude and mean load, on SPF outcomes and compares these to the effects of stress amplitude and mean stress on ratcheting results. The differences in deformation behaviour between ratcheting and small punch fatigue and the effect of biaxiality in SP configuration life is analysed. Finally, to establish a correlation between SPF and ratcheting results, the three life prediction models (Gerber, Goodman, and Smith-Watson-Topper) are examined and a new correlation is proposed by introducing a novel damage parameter.

Study of Some Physical and Antibacterial Properties of Bio-based (PLA)/(PCL) Blend reinforced with ZrO2 Nanoparticles

The aim of this study was to produce flexible films by combining polylactic acid (PLA) and poly(ε-caprolactone) (PCL), and enhance their strength by reinforcing them with different weight percentages (0.75, 1.5, and 2.25%) of zirconium oxide (ZrO2) nanoparticles (NPs) using a solvent casting process. The physical and antibacterial properties of the films were analysed to determine their suitability for use in food packaging. X-ray diffraction (XRD) patterns of the PLA/PCL films containing 2.25% by weight ZrO2 nanoparticles have a peak at an angle of 2θ = 17.18°, accompanied by smaller peaks. This confirms that these thin films have a semi-crystalline structure and that the molecules in the thin films are well dispersed. Scanning electron microscopy (SEM) analysis of the film surfaces reveals that the pure PLA/PCL films exhibit a smooth surface, while the (PLA/PCL/ZrO2NPs) films have a rough surface. The thermal behaviour of the blends through differential scanning calorimetry (DSC) showed fluctuations due to variations in the reinforcement ratio, resulting in changes in the glass transition and melting temperatures. These oscillations indicate changes in the level of crystallinity. ZnO2 has antibacterial properties that promote growth inhibition, making these films more effective in food packaging.

Photopolymerization-based 4D-printing of shape-memory materials containing high-performance polymers

High-performance aromatic heterochain polymers are engineering thermoplastics with exceptional mechanical and thermal properties that have attracted great interest in various areas ranging from aerospace to biomedicine. However, there have been a number of difficulties to 3D-print materials based on such polymers with new promising performance characteristics. Herein, a number of new photosensitive compositions (PSCs) based on high-performance polyetherimide (PEI) or polysulfone (PSU), reactive functional monomer (N,N-dimethylacrylamide) and oligomer (bisphenol A ethoxylate diacrylate) has been developed. It has been shown that the use of the developed PSCs allows the formation of 3D-structures with high printing resolution by LCD 3D-printing. Subsequent thermal post-curing of 3D-printed green-state samples at 250°С for 1 h led to the fabrication of materials with the highest tensile strength (up to 41.9 ± 3.1 MPa), glass transition temperature (141 °C) and thermal stability (above 350 °C). In addition, 3D-printed structures demonstrate high-temperature shape memory effect with shape fixity ratio > 99% and shape recovery ratio up to 97.1%.

Halogen-free epoxy flame retardant & promoter with diimidazole skeleton improves overall properties of epoxy resins

In order to solve the widespread problem in the field of flame retardancy epoxy(FREP), for the deterioration of the overall properties, we designed a novel structural flame retardant & promoter DOPO-CDI and synthesized it using a simple nucleophilic addition one-step method, which exhibits remarkable flame retardant and curing promotion, the flame retardant and promote mechanism of DOPO-CDI on neat EP is illustrated in Fig 0a, which obtained excellent overall properties shown in Fig 0b. Compared with neat epoxy, it has high flame retardancy, low additives results in an limiting oxygen index(LOI) of up to 37.5 % and a V-0 rating of UL-94, a lower curing exothermic peak temperature, a shorter curing time. And in terms of mechanical properties, the excellent strength of epoxy has been further enhanced, flexural strength and tensile strength are increased by 13.3 % and 21.6 % respectively. Moreover, the toughness of epoxy, which is generally lacking, has been greatly improved, in particular, compared with neat epoxy, the impact strength of epoxy with 3 wt% DOPO-CDI increased by 103.6 %. Unlike most FREP, glass transition temperature(Tg) of the epoxy with the introduction of DOPO-CDI raises to 165.6 °C, which is a significant improvement compared to that of the neat epoxy, in terms of combustion behavior, DOPO-CDI has a considerable inhibitory effect on the combustion exotherm and smoke emission. This work explores a way to balance processing, mechanical and thermal properties when preparing FREP, which has great potential for application.

Study of the possibility of using Cardura E10P thinner in epoxy compositions

Rheological, physical-mechanical and thermomechanical properties of binders based on ED-20 epoxy resin with Ethal-45M amine hardener and additives of Cardura E10P glycidyl ether from 5 to 50 wt.% as a diluent have been studied. As the Cardura E10P content increases, the dynamic viscosity of the binder decreases significantly and the gel time increases. The tensile strength of cured samples decreases from 49 MPa to 12 MPa with an increase in the Cardura E10P content from 5 to 30 weight parts, the deformability increases from 14 to 38%, and the glass transition temperature decreases from 67°C to 49°C.

Probabilistic thermal analysis and phase transition temperature optimization for low-rise residential buildings with temperature-adaptive radiative cooling roofs

Probabilistic thermal analysis and phase transition temperature optimization for low-rise residential buildings with temperature-adaptive radiative cooling roofs

Effects of glycation modifications of different glycosylating agents on the molecular structure and gel properties of sheep's hoof gelatin

In this study, we utilized sheep's hoof gelatin as a raw material to modify gelatin by non-enzymatic glycation reactions using five different monosaccharides (D-glucose, D-sorbose, D-fructose, D-ribose, and D-erythrose) and five different polysaccharides (pectin, inulin, carrageenan, xanthan gum, and konjac glucomannan) and comparatively analyzed the properties (rheological properties, textural properties, and thermal stability) of differently glycosylated sheep's hoof gelatin to determine the mechanism of different glycosylating agents on the molecular properties and gel performance of sheep's hoof gelatin. The results showed that the reactivity (DG value) and phase transition temperature (Td value) of gelatin modified with monosaccharide glycosylates were notably higher (p < 0.05) compared to those modified with polysaccharides, resulting in a micro-network structure with finer pore size. Conversely, polysaccharide glycosylation significantly enhanced the mechanical properties and rheological characteristics of gelatin (p < 0.05). The formation of a mosaic network structure in the polysaccharide-glycosylated gelatin group played a pivotal role in enhancing gel properties. Notably, the gel strength (584.62 ± 6.34 g), viscosity (η-value), and gel melting temperature (37.85 ± 0.20°C) of the polysaccharide S-PEC were significantly higher than the other treatment groups (p < 0.05). This research not only provides a new perspective for modifying gelatin derived from sheep's hooves but also offers an important theoretical basis for the exploration and application of gelatin materials in the food industry.

Thermal properties and shape-stabilization of poly(propylene-graft-maleic anhydride)-g-alkyl alcohol comb-like polymeric phase change thermal energy storage materials

In this study, a series of polypropylene-g-maleic anhydride-g-CnH2n+1OH (PMCn, n = 18, 22, 26) comb-like polymeric phase change materials (CPCMs) are fabricated through the solvent-free esterification reaction between polypropylene-g-maleic anhydride(PP-g-MAH)and n-alkyl alcohol with side-chain lengths varying from n = 18, 22 to 26. The pendant side alkyl groups along PP-g-MAH exhibit obvious side-chain crystallization behavior, and phase transition temperature and heat enthalpy of PMCn increase from 60.0 to 82.2 °C and from 53.6 to 118.4 J/g with increasing the side-chain length, respectively. PMCn series CPCMs demonstrate excellent shape stabilization and thermal performance owing to the protection and anchoring role of the PP backbone, and the form-stabilized temperature at 135 °C and 300-time thermal cycles further verify their excellent structural stability and reliability. PMC18 shows a longer thermal buffering time of 362 s and the maximum ΔT at 11.3 °C, and the coated fabric by PMC18 gives a 110 s thermal buffering time during the heat storage process, proving its outstanding thermoregulated ability. The presented PMCn series CPCMs with excellent structural-stabilized performance demonstrate a prospective thermal management application.