Change In Transition Temperature Research Articles

Enhanced Magnetocaloric Properties of the (MnNi)0.6Si0.62(FeCo)0.4Ge0.38 High-Entropy Alloy Obtained by Co Substitution

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, Mn0.6Ni1−xSi0.62Fe0.4CoxGe0.38 (x = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature Ni2In-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why chexagonal/ahexagonal (chexa/ahexa) gradually increases upon Co substitution, while phase transition temperature (Ttr) and isothermal magnetic entropy change (ΔSM) tend to gradually decrease. In particular, the x = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kg−1K−1 at 309 K for 5 T and an adiabatic temperature change (ΔTad) of 8.6 K at 306.5 K. Moreover, the x = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large ΔSM and ΔTad may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material.

Study on the UV aging resistance of ZnO‐modified epoxy resin by experiments and MD simulation

AbstractThis study investigates the impact of zinc oxide nanoparticles on epoxy resin systems and the ultraviolet (UV) aging resistance of modified epoxy resin composites using molecular dynamics (MD) simulations and experimental methods. Initially, various epoxy resin cross‐linking models are established through MD simulations to understand the influence of different nano ZnO contents on resin modification, further validated by experiments. Subsequently, the UV radiation resistance of nano ZnO–epoxy resin composites is assessed by subjecting them to high‐intensity UV radiation equivalent to 3 years of natural environmental conditions, analyzing changes in tensile properties, impact performance, hardness, and glass transition temperature of epoxy resin before and after UV radiation exposure. The findings suggest that the addition of nano zinc oxide reduces the impact of UV radiation on epoxy resin, with optimal UV radiation resistance observed at a nano zinc oxide mass fraction of 0.3 wt%.

Investigation of the substitution of mercury by silver in Ag2S-HgS-GeS2 glasses: Macroscopic, electrical and vibrational properties

The evolution of structure and physical properties was investigated in the (Ag2S)x(HgS)50-x(GeS2)50 system. It was found that the density increases with increasing silver sulfide. The DSC data show a non-monotonic change of the glass transition temperature, Tg, from 243 °C (x = 0) to 301 °C (x = 50) with the minimum at 231 °C for x = 10 sample. The dual structure of HgS, which consists of the presence of dimorphic tetrahedral and chain forms of HgS, is found to be responsible for the non-monotonic change of the Tg. An increase in silver content leads to a significant enhancement of ionic conductivity from ∼10−14 S.cm−1 (x = 0) to ∼10−3 S.cm−1 (x = 50). The gradual structural evaluation is evidenced by the disappearance of the main Raman feature at ≈300 cm−1 related to the Hg-S stretching and the emergence of two contributions for silver-rich glasses at ≈370 cm−1 and at ≈400 cm−1.

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.

Fabrication of free standing nano-SiO2 incorporated solid polymer electrolytes based on poly(vinyl) chloride

AbstractFree standing nanocomposite polymer electrolytes (NCPEs) based on the polymer host poly(vinyl) chloride (PVC) were successfully prepared using the solution casting technique. Lithium nitrate (LiNO3) and nano-sized silica (SiO2) (< 100 nm) were employed as the electrolyte and filler, respectively. Impedance studies revealed a maximum ionic conductivity value of 1.226 × 10−4 S/cm at room temperature for the PVC/LiNO3 with 5 wt.% nano-SiO2. X-ray diffraction (XRD) analysis verified the sample’s amorphous nature. Dielectric permittivity and relaxation time values were consistent with impedance results. Additionally, parameters such as diffusion coefficient, mobile concentration, and mobility were evaluated for the prepared samples. Differential scanning calorimetry (DSC) studies confirmed a change in glass transition temperature (Tg) of PVC/LiNO3/SiO2 sample. The scanning electron micrograph (SEM) images revealed a honeycomb morphology, indicating ease of Li+ ion transportation.

Thermoresponsiveness Across the Physiologically Accessible Range: Effect of Surfactant, Cross-Linker, and Initiator Content on Size, Structure, and Transition Temperature of Poly(N-isopropylmethacrylamide) Microgels.

The influence of surfactant, cross-linker, and initiator on the final structure and thermoresponse of poly(N-isopropylmethacrylamide) (pNIPMAM) microgels was evaluated. The goals were to control particle size (into the nanorange) and transition temperature (across the physiologically accessible range). The concentration of the reactants used in the synthesis was varied, except for the monomer, which was kept constant. The thermoresponsive suspensions formed were characterized by dynamic light scattering, small-angle X-ray scattering, atomic force microscopy, and rheology. Increasing surfactant, sodium dodecyl sulfate content, produced smaller microgels, as expected, into the nanorange and with greater internal entanglement, but with no change in phase transition temperature (LCST), which is contrary to previous reports. Increasing cross-linker, N,N-methylenebis acrylamide, content had no impact on particle size but reduced particle deformability and, again contrary to previous reports of decreases, progressively increased the LCST from 39 to 46 °C. The unusual LCST trends were confirmed using different rheological techniques. Initiator, potassium persulfate, content was found to weakly influence the outcomes. An optimized content was identified that provides functional nanogels in the 100 nm (swollen) size range with controlled LCST, just above physiological temperature. The study contributes chemistry-derived design rules for thermally responsive colloidal particles with physiologically accessible LCST for a variety of biomedical and soft robotics applications.

A versatile method for facile and reliable synthesis of colloidal particles with a size and composition gradient

Abstract Colloidal particles play a pivotal role in numerous applications across various disciplines, many of which necessitate precise control over particle size and size distribution. Seeded growth reactions have been established as effective methods for reproducibly accessing tailor-made particles. However, conventional batch-wise syntheses only yield discrete particle sizes. With the increasing focus on complex structures in current research, there is a demand for innovative and adaptable techniques to produce colloidal particles with precise sizes and size distributions. The Controlled Emulsion Extraction Process (CrEEP) is capable of addressing this challenge. Here, we present in detail how this synthesis works and demonstrate its reliability and versatility. Our approach exploits the time-dependent particle growth and enables accessing dispersions of controlled particle size distributions. We highlight these possibilities through a variation of the monomer feed and feed composition, resulting in gradual changes in both size and glass transition temperature, respectively. Beyond its application to polymer particles, CrEEP can be seamlessly extended to other seeded-growth mechanisms, such as the silica Stöber synthesis. Consequently, the Controlled Extraction Stöber Process (CrESP) similarly yields a size gradient, showcasing the generality of this synthetic advancement. Graphical abstract

Assembly of functional carboxymethyl cellulose/polyethylene oxide/anatase TiO2 nanocomposites and tuning the dielectric relaxation, optical, and photoluminescence performances

Nanocomposite films consisting of carboxymethyl cellulose, polyethylene oxide (CMC/PEO), and anatase titanium dioxide (TO) were produced by the use of sol-gel and solution casting techniques. TiO2 nanocrystals were effectively incorporated into CMC/PEO polymers, as shown by X-ray diffraction (XRD) and attenuated total reflectance fourier transform infrared (ATR-FTIR) analysis. The roughness growth is at high levels of TO nanocrystals (TO NCs), which means increasing active sites and defects in CMC/PEO. In differential scanning calorimetry (DSC) thermograms, the change in glass transition temperature (T g) values verifies that the polymer blend interacts with TO NCs. The increment proportions of TO NCs have a notable impact on the dielectric performances of the nanocomposites, as observed. The electrical properties of the CMC/PEO/TO nanocomposite undergo significant changes. The nanocomposite films exhibit a red alteration in the absorption edge as the concentration of TO NCs increases in the polymer blend. The decline in the energy gap is readily apparent as the weight percentage of TO NCs increases. The photoluminescence (PL) emission spectra indicate that the sites of the luminescence peak maximums show slight variation; peaks get wider, while their intensities decrease dramatically as the concentration of TO increases. These nanocomposite materials show potential for multifunctional applications including optoelectronics, antireflection coatings, photocatalysis, light emitting diodes, and solid polymer electrolytes.

Optimizing biobased thermoset resins by incorporating cinnamon derivative into acrylated epoxidized soybean oil

The study successfully developed thermoset materials utilizing acrylate epoxidized soybean oil (AESO) and allyl cinnamate (ACIN) with tert-butyl peroxybenzoate (TBPB) as the initiator. Isothermal curing at temperatures between 110 °C to 140 °C of the developed formulations, showed that higher temperatures accelerated the conversion process. The higher curing temperature increased the degree of conversion, leading to obtain the best flexural strength for samples cured at 130 °C. However, samples cured at 120 °C exhibited better impact properties due to a lower degree of conversion, which allows for a more mobile reticular network. In addition, morphological observations confirmed these mechanical property trends. Dynamic thermal characterization revealed changes in glass transition temperature and exothermic reactions due to unreacted products appeared for materials cured at low temperature. Increasing curing temperature allowed to enhance thermal stability by increasing molecular weight. Finally, thermomechanical analysis confirmed stiffness and glass transition temperature increases observed during flexural tests and thermal characterization.

Pendant Group Functionalization of Cyclic Olefin for High Temperature and High-Density Energy Storage.

High-temperature flexible polymer dielectrics are critical for high-power-density energy storage and conversion under harsh operating conditions. These types of dielectrics will need to simultaneously possess a high bandgap, dielectric constant and glass transition temperature - a substantial challenge when designing novel dielectric polymers. In this work, by varying halogen substituents of an aromatic pendant hanging off a bicyclic mainchain polymer, a class of high-temperature olefins with adjustable thermal stability are obtained, all with uncompromised large bandgaps. Halogens substitution of the pendant groups at para or ortho position of polyoxanorborneneimides (PONB) imparts it with tunable high glass transition temperature from ∼220 to 245°C, while with also moderate dielectric constant of ∼ 2.8-3.0 and high breakdown strength of ∼625-800MV/m. A high energy density of 7.1 J/cc at 200°C is achieved with p-POClNB, representing the highest reported energy density among all-organic homo-polymer dielectrics. Molecular dynamic simulations and ultrafast infrared spectroscopy were used to probe the free volume element distribution and chain relaxations of the polymers to provide insights to the dielectric thermal properties. An increase in free volume element is observed with the change in the pendant group from fluorine to bromine at the para position; however, a decrease in free volume element is observed as we change the pendant group from fluorine to chlorine at the ortho position because of the steric hindrance. Overall, the dielectric constant and band gap remain stable while the glass transition temperature changes more obviously. Consequently, by proper designing the pendant groups, the thermal stability of PONB can be improved for harsh condition electrification. This article is protected by copyright. All rights reserved.

Addition of calcium carbonate in the synthesis of flexible polyurethane foams

Within all their variability, foams constitute the largest segment in the polyurethane industry. Polyurethane is composed mainly of isocyanate (-N=C=O) and polyol (-OH) functional groups, presenting different characteristics by adding fillers. This polymer has a wide range of applications such as adhesives, coatings, varnishes, elastomers and foams. Aiming improvements in its thermal properties, calcium carbonate addition was investigated in proportions of 12.5%, 25% and 37.5% (w/w). This filler is widely used to change the properties of polymers, as it is easily found in nature and has a low cost. For the synthesis of polyurethane samples, isocyanate and polyol were reacted using "one shot" process. The obtained results demonstrated the change in the glass transition temperatures (Tg) of the material to higher values, which indicates a decrease in the mobility of the polymer chains. Also, an increase in decomposition temperature was observed via differential scanning calorimetry (DSC). With Fourier transform infrared spectroscopy (FTIR) analysis, it was possible to analyze that the material was successfully synthesized by the appearance of the characteristic bands of PU foams. Furthermore, with the addition of calcium carbonate, it was possible to identify the presence of two phases, which indicate that the material underwent changes in its crystallinity, identified through X-ray diffraction (XRD) analysis. Finally, it was possible to observe via optical microscopy (OM) analysis that the addition of filler significantly changed the morphology of the foams.

Evaluation of Viscoelastic Performance and Molecular Structures of Natural Rubber/NBR Blends Reinforced by Carbon Black and Nano-Silica

This study focuses on the evaluation of the dynamic mechanical properties, molecular structure, density, hardness, swelling behavior of natural rubber blends (NR) and nitrile rubber (NBR) reinforced with carbon black and/or nano-silica. An experimental work has been conducted to study of the effects of increasing NR content and incorporating nano-silica on the mechanical properties and molecular structure were studied using dynamic mechanical analysis (DMA) and Fourier transform infrared (FTIR) spectroscopy. The results show that increasing the NR content and/or incorporating nano-silica into the elastomer leads to a higher storage modulus with no significant change in the glass transition temperature. FTIR analysis indicates the compatibility of the polyblends and the presence of oxidation of the main polymer chain generated during the grinding of the rubber. Additionally, the results of the swelling study demonstrate that stronger molecular interactions occur on the surface of the nano-silica between the nitrile radicals in the NBR and the silanol (Si-OH) radicals. These findings suggest that blending NR and NBR with carbon black and/or nano-silica can improve the mechanical properties and compatibility of the resulting polyblends, with potential applications in the development of advanced elastomeric materials.

Properties and Performance of Epoxy Resin/Boron Acid Composites.

This research study focused on the effect of adding boric acid to epoxy resin in order to obtain a composite material with improved properties and performance. To this end, a fine powder of boric acid (H3BO3) was introduced into epoxy resin in different amounts, i.e., 0.5 g, 1.0 g, and 1.5 g. As the matrix of the epoxy composites, styrene-modified epoxy resin based on bisphenol A (BPA) (Epidian 53) was used. It was cross-linked with two types of curing agents, i.e., an amine (ET) and a polyamide (PAC). The mechanical properties of the obtained epoxy composites (in terms of compressive strength, compressive modulus, and compressive strain) were determined at room temperature in order to assess the effect of the addition of boron acid and of the type of curing agent employed to cure the epoxy on these characteristics. Calorimetric measurements were made to highlight any changes in the glass transition temperature (Tg) as a result of the addition of boric acid to epoxy resin. Finally, flammability tests were performed on both Epidian 53/PAC and Epidian 53/ET epoxy composites to analyze their fire behavior and consequently establish the effectiveness of the selected additive as a flame retardant.

Investigation the optical and structural properties of Mn-doped Sb2S3 nanocrystals embedded in host glass

The search for earth-abundant and non-toxic elements is essential for the manufacture of sustainable optical devices. In this context, dilute magnetic semiconductor (DMS) xMn-doped Sb2S3 nanocrystals (NCs) embedded in host glass were synthesized by the fusion method. Differential Thermal Analysis shows evidence of Sb2S3 phase crystallization peak and changes in glass transition and crystallization temperatures of the host glass with the presence of xMn-doped Sb2S3 NCs. Transmission electron microscopy images show the formation of xMn-doped Sb2S3 NCs with increasing size (2.1–3.8 nm) as a function of concentration (x = 0.00 to 0.40), respectively. X-ray diffraction measurements reinforced the evidence for the orthorhombic structure of xMn-doped Sb2S3 NCs embedded in glass. Energy dispersive X-ray spectroscopy analyses confirm the S, Sb and Mn precursor elements of DMS NCs. Atomic and magnetic force microscopy measurements show the magnetic contrast patterns resulting from the incorporation of Mn atoms into the Sb2S3 structure. The electronic paramagnetic resonance spectrum confirms the presence of Mn2+ ions (3d5) located in the crystal field of the Sb2S3 semiconductor due to six hyperfine transitions. The redshift of the Raman vibrational mode (1Ag) with increasing xMn concentration gives strong evidence for the presence of Mn2+ ions in sulfur vacancies (VS) in the Sb2S3 unit cell. Optical absorption and photoluminescence (PL) spectroscopy measurements for xMn-doped Sb2S3 NCs show the subtle tunable redshift of the band gap and excitonic recombination in the green-red region, with increasing x concentration. PL confirms that dopant Mn2+ ions fill VS2 that are dominant in Sb2S3. Therefore, the position of the energy states after the increasing concentration of Mn2+ dopant ions gives rise to insight into luminescence for future research scenarios and applications involving sustainable DMS NCs.

Thermophysical Properties of Composite Metal-Filled Copolymers of Polyvinylpyrrolidone

The effect of the presence of finely dispersed metal fillers of various natures (Zn, Co, Ni) on the thermophysical characteristics (Vick heat resistance, glass transition temperature) of polyvinylpyrrolidone block copolymers with 2-hydroxyethylmethacrylate was studied. It was found that the heat resistance of the obtained composites significantly exceeds the heat resistance of unfilled copolymers and is in the range of 360-395K, depending on the nature and content of the metal filler. The change in heat resistance correlates with the change in glass transition temperature, which was evaluated according to the results of thermomechanical and dynamic mechanical thermal analyses. The results of this work are an additional source to characterize the structure of metal-filled copolymers: they confirm the participation of metal filler particles in the formation of the nodes of the copolymer spatial network, and also prove the formation of a different polymer network structure in the interfacial layer on the surface of the metal particle and in the polymer volume.

Advancing additive manufacturing: 3D‐printing of hybrid natural fiber sandwich (Nona/Soy‐PLA) composites through filament extrusion and its effect on thermomechanical properties

AbstractThe additive manufacturing technique represents a technological advancement post the industrial revolution, enabling the development of intricate products with minimal waste. In the automotive sector, polymer extrusion‐based additive manufacturing is predominantly employed for part customization. Recently, reinforced polymer matrices have been used to enhance structural integrity, primarily utilizing synthetic materials. Due to environmental concerns, some recent studies have explored the incorporation of natural fiber reinforcement in polymer matrices for 3D‐printed products. Most research has focused on filler reinforcement, limiting investigations to a single type of reinforcement. To bridge this gap and enhance composite performance, our research introduces a novel method for 3D printing composites. This involves stacking sequences using two different natural fiber‐reinforced polylactic acid (PLA) filaments, namely Nona and Soy, respectively. Mechanical testing reveals that the stacking sequence significantly influences the mechanical properties of the 3D‐printed composites. The 3D‐printed composite with Soy/PLA skin stacks exhibits the highest tensile strength of 74.82 MPa. Thermal analysis shows minor changes in glass transition temperature (Tg) and a consistent degree of crystallinity (10.01%). Notable differences in thermal expansion are observed due to the stacking sequence. Fatigue analysis demonstrates the durability of hybrid composites, enduring over 42,000 cycles with minimal deformation compared with to pure fiber‐reinforced 3D‐printed composites. Morphological analysis reveals excellent fiber–matrix interaction and bonding between stacks. The observations confirm that the developed material can be potentially used for developing structurally enhanced composites for lightweight applications. Moreover, the proposed methodology can be adapted for different 3D printing matrices, including robotic printing with multiple axes, making it suitable for various industrial sectors.Highlights Utilization of 3D printing technology for the development of agro‐waste fiber products. Hybridizing the 3D‐printed composite enhanced the fatigue life. New additive manufacturing technique for developing structurally enhanced composites.

Analysis of the Curing Behavior of Cyanate/Epoxy Resins for Fusion Magnets

ITER IF coils and the German WX-7 star simulator fusion reactor both use cyanate ester/epoxy resin as the matrix material for their insulation structure. The main reason is that cyanate ester/epoxy resin insulation materials have low-temperature mechanics and radiation resistance, and have extremely low rheological properties and long applicability periods. However, high-energy polymerization will occur when the two are mixed, releasing a huge amount of heat. This study used different molds to prepare cyanate ester/epoxy resin (mass ratio 4:6), and used DSC (Differential Calorimetry Scanning) thermal analyzer and temperature monitoring to study the curing behavior and thermal stability of cyanate ester-modified epoxy resin-based materials. After multiple optimizations, the resin was completely cured within a controllable range, and there was no significant change in the glass transition temperature before and after adjustment.

Impact of water absorption on the creep performance of epoxy/microcrystalline cellulose composites

AbstractRecently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post‐conditioning anomalous effect of moisture uptake on their mechanical and dynamic‐mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog‐bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier‐transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long‐term properties of the composites.

Tailoring the physical parameters of nematogen using non-mesogenic ferromagnetic unit: dielectric and photoluminescence study

Liquid crystals are self-organized anisotropic fluids which exhibit ordered states ranging from nematics to smectics/hexatics. Hybridized liquid crystals with nanoparticles broaden the research area in finding the novel functional devices. Reported herein, the study of highly stable room temperature nematic liquid crystal E7 and carbon-coated cobalt (Co) nanoparticles. Dispersion of 0.50 wt.% Co into E7 has been introduced to tailor the physical parameters of host E7. Dielectric studies have been performed in planar as well as homeotropic cells in the frequency range of 20 Hz–10MHz while photoluminescence spectra have been recorded at excitation wavelength of 325 nm in planar cells. Dielectric studies reveal the change in phase transition temperature and molecular dynamics associated with magnetic nanoparticles doped liquid crystals. Quenching in photoluminescence intensity has been observed with the inclusion of Co nanoparticles due to the formation of non-radiative channels in the composite system. The intercalation of Co nanoparticles into E7 studies manifests the strong correlation between liquid crystals and nanoparticles. Allocation of magnetic attributes onto liquid crystal molecules finds potential applications in advanced magnetic materials, information devices and optical devices.

Thickness‐dependent glass transition temperature of hydroxyethyl cellulose thin films based on dielectric properties

AbstractHydroxyethyl cellulose (HEC) thin films with a molecular weight of 720,000 g/mol deposited by thermal evaporation in a thickness range of 250, 500, and 750 nm were measured in a frequency range of 1–105 Hz and a temperature range of 233–373 K for dielectric characterization with increments of 10 K. Dielectric results were used to derive and evaluate the glass transition temperature and ductility, which are essential parameters for structural analysis. Results showed that the thickness of HEC thin films was an effective parameter on dielectric and structural properties. Because of the increasing thickness, the dielectric constant has values between 22 and 143 at 1 kHz, and glass transition temperature and ductility change between 211–175 K and 15–20, respectively. Based on the literature and the compatible results, the main effect of these variations could be dead layers and voids in structure. The effect of the dead layer gave an important idea about the adjustability of mechanical properties of HEC thin films depending on the thickness. In this way, it would be possible to use these thin films deposited from HEC with 720,000 g/mol molecular weight, especially in drug delivery, electrophoresis technologies, biomedical devices, and coverage applications.