Thermal Stability Parameters Research Articles

The use of chain extenders as processing aids in the valorization of single-use polylactide (PLA) products by rotomolding

Biodegradable plastics in single-use products have increased in popularity as a way to reduce the negative environmental impact of conventional plastics and meet the tightening law regulations. However, their recyclability needs to be assessed, as the environmental behavior of single-use plastics, even if compostable, is not negligible. Polylactide (PLA) is susceptible to thermal, oxidative, hydrolytic, and mechanical degradation during reprocessing, so the conditions of such cycles must be accurately controlled. The necessity of using additives to reduce such degradations during rotational molding, a process with long cycle times and oxidizing atmosphere, has been demonstrated. Chain extenders based on a carbodiimide (Bioadimide® 100 - KI), a methylene diphenyl diisocyanate (MDI), and a polystyrene-acrylic copolymer (Joncryl® ADR-4368c - J) have been added to post-consumer PLA wastes. It has been demonstrated that these three chain extenders enabled obtaining a higher molecular weight of the reprocessed polymer, compared to the ∼50% reduction for the neat PLA. The use of carbodiimide yielded the most similar performance to that of unprocessed raw material. All samples provided adequate thermal stability and processing parameters for the rotational molding. Carbodiimide is considered the most efficient additive, as it increases the molecular mass of the polymer as it remains unchanged after processing. Similarly, KI-modified PLA rheological behavior remains unchanged after processing, which means this compound can reduce thermooxidative and hydrolytic degradation reactions. Thus contributing to the achievement of improved processability and better performance; in particular, impact strength increased from 1.06 ± 0.56 for PLA to 8.12 ± 2.28 kJ/m2 for KI-modified PLA, and toughness of 5.36 ± 1.61 to 61.49 ± 8.01 J/mm3, respectively, leading to rotomolded items without structural defects. On the opposite, the use of Joncryl® and MDI led to structural defects in the rotomolded parts despite a higher molecular weight of the polymer, which resulted in poor mechanical properties, although better than PLA without any additive. All three chain extenders resulted in an amorphous PLA structure with increased glass transition temperature and improved thermal stability, which correlated with the reduced emissions of volatile compounds compared to neat recycled PLA. The presented findings significantly contribute to a better understanding of PLA and its modifications at a molecular scale required for its efficient and possibly environmentally burden-free reprocessing. Gathered knowledge will be crucial for optimizing its environmental performance and widening its applications, particularly in a process with long cycle times and oxidative character, such as rotational molding.

Influence of Gamma irradiation on shape memory polymer nano-composite for satellite deployment mechanism

This research investigates the impact of gamma irradiation on epoxy-MWCNT nanocomposites for satellite deployment mechanisms. Nanocomposites, enhanced with surfactants, were meticulously prepared and subjected to controlled gamma irradiation (250–1000 kGy) utilizing the Cobalt-60 facility Industrial Mega Gamma-1 at NCRRT in Egypt. Surface tension measurements explored surfactant effects on epoxy-MWCNT composites in acetone. Acetone reduced tension from 26.7 to be 24.2 (mN/m). Surfactants (Tween 80, SDS) effectively lowered tension (24.4 mN/m), while surfactant-free systems had higher tension (25.1 mN/m). Cationic surfactant (CTAB) slightly increased tension (25.4 mN/m) but aided MWCNT dispersion. Nonionic and anionic surfactants showed superior dispersing power, aligning with MWCNTs and enhancing dispersion. Thermogravimetric analysis (TGA) unveiled alterations in the thermal stability of epoxy-MWCNT nanocomposites induced by radiation, particularly evident at elevated doses (500 and 1000 kGy). Notably, surfactant-modified specimens exhibited discernible effects on various thermal stability parameters. DMA analysis revealed radiation-induced changes in viscoelastic properties. Unirradiated epoxy exhibited a Tg of 58 °C, while 250 kGy irradiation enhanced crosslinking (Tg: 64 °C). Higher doses (500 kGy, 1000 kGy) caused marginal Tg changes. Surfactant-modified samples showed varied effects, with Tween 80 emphasizing its role in phase separation. Results highlighted radiation’s influence on stiffness and energy dissipation. Shape memory behavior indicated increased recovery time with higher doses, except at 250 kGy. Epoxy-MWCNT exhibited a stable recovery time, suggesting a MWCNT stabilizing effect. Fixation rates consistently reached 100%, indicating improved shape recovery influenced by MWCNTs and surfactants. This study provides insights into optimizing nanocomposites for satellite deployment applications.

Improving flame resistance and shielding properties for cross-linked polyethylene (XLPE) using nanoclay filler

Polymers play an essential role in both industry and medical fields due to their diverse and adaptable properties. In this work, prepared crosslinking polyethylene (XLPE) samples with hydrophilic bentonite nanoclay fillers (H2Al2O6Si) at concentrations of 0, 1, 2.5, 4, and 5 wt% enhance their flame-retardant and radiation shielding efficiency. The research investigated flame retardancy and thermal stability parameters. The XLPE/H2Al2O6Si nanocomposite polymer sheets were exposed to a collimated beam of fast neutrons using an Am/Be neutron source (5 Ci) and to gamma radiation using a 137Cs point source (5 μCi) to assess their radiation shielding properties. The study found that uniform dispersion of nanoclay particles enhanced the thermal properties of the composite, forming a char layer that acted as a barrier, slowing thermal decomposition and reducing the heat release rate. Limiting oxygen index (LOI) increased from 28% to 34%, and burning rate improved with higher nanoclay concentrations. Additionally, absorption and optical band gap calculations decreased with increasing filler concentrations. Radiation attenuation capabilities increased by approximately 40% for neutrons and 30% for gamma radiation compared to pure XLPE. The study concluded that incorporating nanoclay fillers into XLPE enhances its shielding capabilities and improves flame resistance properties, making the prepared samples suitable for various industrial applications.

An Investigation of the Photonic Application of TeO2-K2TeO3-Nb2O5-BaF2 Glass Co-Doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 at 1.54 μm Based on Its Thermal and Luminescence Properties.

A glass composition using TeO2-K2TeO3-Nb2O5-BaF2 co-doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 was successfully fabricated. Its thermal stability and physical parameters were studied, and luminescence spectroscopy of the fabricated glasses was conducted. The optical band gap, Eopt, decreased from 2.689 to 2.663 eV following the substitution of Ho2O3 with Yb2O3. The values of the refractive index, third-order nonlinear optical susceptibility (χ(3)), and nonlinear refractive index (n2) of the fabricated glasses were estimated. Furthermore, the Judd-Ofelt intensity parameters Ωt (t=2,4,6), radiative properties such as transition probabilities (Aed), magnetic dipole-type transition probabilities (Amd), branching ratios (β), and radiative lifetime (τ) of the fabricated glasses were evaluated. The emission cross-section and FWHM of the 4I13/2→4I15/2 transition around 1.54 μm of the glass were reported, and the emission intensity of the visible signal was studied under 980 nm laser excitation. The material might be a useful candidate for solid lasers and nonlinear amplifier devices, especially in the communications bands.

Investigating the influence of chromium layer thickness on thermal stability, adhesion and agglomeration of Cr/Ag/Cr sandwich layers in microelectromechanical systems (MEMS)

This study explores the influence of chromium layer thickness on the thermal stability and agglomeration of Cr/Ag/Cr sandwich layers used in MEMS applications. Achieving uniform and consistent deposition of thin films is crucial for optimal device performance. Magnetron sputtering, a technique offering precise control over film properties, is commonly employed for depositing thin films in MEMS. Silver is a popular choice due to its desirable properties, but it tends to agglomerate at high temperatures. The researchers investigated the effect of chromium layer thickness on thermal stability and agglomeration. They deposited chromium layers of varying thicknesses onto silicon substrates, followed by a silver layer and another chromium layer to create a sandwich structure. Annealing was performed at different temperatures to assess thermal stability and prevent silver agglomeration. Thermal stability was evaluated by measuring electrical resistance using a four-point probe method, and surface topography was analyzed using a non-contact atomic force microscope. The goal was to identify the optimal chromium layer thickness to minimize agglomeration and maximize thermal stability. The results showed that a sandwich structure with a 5 nm top chromium layer (Si/Cr (5 nm)/Ag (100 nm)/Cr (5-10-15-20 nm)) exhibited decreased adhesion force with increasing annealing temperatures. The use of a chromium sandwich layer significantly reduced surface roughness, as indicated by reductions in Ra and RMS values. A 15 nm thick chromium layer above and below the silver layer provided the best thermal stability and prevented silver agglomeration, resulting in the highest degree of adhesion. This thickness also yielded optimal surface parameters for the chromium sandwich layers at the annealing temperatures. In conclusion, the study demonstrates that the thickness of the chromium layer influences thermal stability, agglomeration, and surface parameters in MEMS applications and enables better control over thin film deposition.

Insights into the oxidative thermal stability of mesoporous triazine‐based organic polymers: Kinetics and thermodynamic parameters

AbstractThis study investigates the thermal degradation kinetics of mesoporous triazine‐based polymers, namely triazine‐amine and triazine‐ether polymers. The synthesis, physicochemical characterization, and catalytic applications of these polymers were discussed in our previous report. Herein, the thermal stability parameters, including kinetic triplets and thermodynamic parameters, were determined using thermogravimetric analysis (TGA) and non‐isothermal mathematical approximations such as Coats‐Redfern, Broido, and Horowitz–Metzger methods. Triazine‐ether polymers exhibit thermal stability within the range of 200°C–300°C, while triazine‐amine polymer demonstrates superior thermal stability, reaching up to 450°C. According to the Coats‐Redfern method, the degradation follows reaction orders of 0.5 ≤ n ≤ 1. The activation energy of triazine‐amine polymer is notably high, particularly at the third degradation stage (e.g., 89.0 kJ/mol by the Broido method), attributed to its high nitrogen content. Conversely, the higher carbon content of triazine‐ether polymers reduces their activation energy to approximately 30 kJ/mol at all stages and thus, facilitates the degradation process. Thermodynamically, the degradation process is favorable yet non‐spontaneous, with intermediate states of the polymers exhibiting higher entropy, indicative of their enhanced degradation capability.

Synthesis, structural and antimicrobial studies of transition metal complexes of a novel Schiff base ligand incorporating 1,2,4-triazole and 4-(benzyloxy)benzaldehyde moieties

A Schiff base ligand named 4-(((5-mercapto-4H-1,2,4-triazole-4-yl)imino)methyl)-(benzyloxy)benzene (HL) and its bioactive series of Ni(II), Cu(II), Zn(II) and Cd(II) metal complexes having 1:1 and 2:1 ligand-to-metal ratio, have been synthesized. All the synthesized compounds were fully characterized by IR, 1H-NMR, elemental analysis, absorbance (UV-Vis.) and mass spectra. Furthermore, the molecular structure of the Schiff base was established by single-crystal X-ray diffraction analysis. Additionally, computational investigations of the compounds were conducted using the DFT/B3LYP method. This analysis involved the determination of FMO energy values, as well as the calculation of quantum chemical parameters. The binding effect of metal ions on the ligand's fluorescence intensity was probed using fluorescence spectroscopy. The thermal stability and kinetic parameters of the complexes were determined using TGA (Thermogravimetric Analysis) analysis via the Coats–Redfern method. The docking studies, actively explored the interaction between Schiff base ligand and protein receptor molecules of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. To assess the therapeutic potential, an in silico ADMET model was employed, revealing that the synthesized molecules exhibit drug-like properties. The Schiff base and all the derived metal complexes were screened for their antimicrobial potential against bacterial species like Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and fungus Candida albicans.

Investigation of thermodynamical, electro-optical and dielectric properties of nematic liquid crystals dispersed with low-concentration barium titanate nanoparticles

ABSTRACT A liquid crystals nanoparticles composite was prepared by dispersing barium titanate nanoparticles (BT-NPs) into a multi-component liquid crystalline material having wide range room temperature nematic phase. The thermodynamic, optical textures, electro-optical and dielectric properties of the composite sample were studied along with pristine materials. Isotropic to nematic phase transition temperature was enhanced for nano-composites as observed from thermodynamic, optical textures and dielectric investigations. Effect of BT-NPs dispersion on various display parameters of nematic liquid crystals, namely, threshold voltage, dielectric anisotropy, DC conductivity and splay elastic constant has been explored. A relaxation mode in kHz frequency range has been observed for pure and nano-composites samples, which varies with temperature and follows Arrhenius behaviour. DC conductivity enhances approximately fivefold for BT-NPs dispersed samples. The host liquid crystalline material has nematic ordering which supports alignment of BT-NPs parallel to the nematic director which consequently improves thermal stability, dielectric and electro-optical parameters of the nano-composite system.

Oxidation Mechanism and Surface Characterization of Pyrolytic Graphite in Simulated Air for Pyrochemical Reprocessing Application

Accidental air ingress into the containment chamber of pyrochemical reprocessing of spent nuclear fuels can cause severe oxidation of graphite components. Pyrolytic graphite (PyG) coating on conventional high-density graphite (HDG) is proposed for protection against oxidation, molten salt, and molten metal corrosion. The aim of the present study is to evaluate the thermal stability and kinetic parameters and propose a suitable oxidation mechanism of PyG under simulated air using thermogravimetry analysis (TGA). In dynamic oxidation, a linear increase in the oxidation onset, peak, and burnout temperature is observed for PyG synthesized at increasing pyrolysis temperature from 1200 to 2400°C except for 1400°C. The isothermal oxidation study showed a similar trend i.e., a decrease in the linear oxidation rate constant value for any given isotherm with increasing pyrolysis. The Arrhenius plot showed two-stage oxidation regimes operating between 600 to 1000°C. In regime-I, between 600 to ∼800°C controlled by surface chemical reaction kinetics, the activation energy is measured between 100-200 kJ.mol−1. The graphite-oxygen reaction initiates and propagates preferentially along the prismatic planes at the sample edges, where the dangling bonds of stacked graphite layer structures are exposed. In regime-II operating above ∼800°C, the surface reaction rate is infinitely faster, and the diffusional mass transport becomes a rate-limiting factor. In this regime, the graphite-oxygen initiates by pore formation on defective reactive sites on the bulk surface and propagates by pore-widening and pore-coalescence mechanism. The observed differences in the oxidation rates for different pyrolysis PyG attributed to its intrinsic material properties are investigated. This work provides new insights into the oxidation mechanism of the PyG during accidental air ingress in a pyrochemical reprocessing plant.

Rowanberry/vermiculite modified rigid polyurethane foams

Rigid polyurethane (PU) foams were modified with rowanberry/vermiculite fillers. The impact of fillers on selected properties of composites, such as rheological properties (dynamic viscosity, foaming behavior), mechanical properties (compressive and flexural strength, toughness), thermal properties (temperature of thermal decomposition stages, char residues at 600°C), flame retardancy (ignition time IT, total heat, and smoke release THR and TSR, maximum average rate of heat emission MARHE) was investigated. The results show that the incorporation of rowanberry/vermiculite fillers improves the properties of polyurethane foams. For instance, compared with the reference foam, modified foams showed increased synthesis times and higher values of apparent density, which then influenced the mechanical properties. Compared to the unmodified foam, modified foams showed an improvement in compressive strength (up to 7.8%, measured parallel to the foam growth direction), flexural strength (up to 5.8%), and toughness (up to 6.8%). Most importantly, the modified foams showed improved thermal stability and flammability parameters such as elongated ignition time, lowered values of THR, TSR, and MARHE parameters.

Clay powder in polymer composite membranes enhanced the performance of direct methanol fuel cells

Polyvinyl alcohol has the potential to be used in fuel cell membranes due to its chemical, mechanical, and membrane-forming capabilities, as well as its higher hydrophilicity and low methanol permeability. However, the pure PVA membrane has a lower proton conductivity than the NafionTM membrane. With the addition of some ceramic fillers, PVA can be a possible alternative to NafionTM membranes. Therefore, we used the solution method to prepare three polyvinyl alcohol-based composite membranes with the following compositions: a) 5 wt% PVA (polyvinyl alcohol), b) 5 wt% PVA/2 wt % PEG (polyethylene glycol)/wt.1% silicon dioxide (SiO2) nanoparticles, and c) 5 wt% PVA/2 wt% PEG/wt.1% clay powder. The membranes were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDX), oxidative stability, ion exchange capacity, water absorption characteristics, conductivity, and permeability. FITR, EDX, and SEM confirmed the successful fabrication of the composite membrane, while TGA demonstrated membrane thermal stability and other parameters relevant to fuel cell membranes. The methanol permeability of the membrane is pure 5 wt % PVA, 5 wt%PVA/2 wt%/1 wt% SiO2, and 5 wt% PVA/2 wt% PEG/wt.1% Clay measured 2.37 × 10−6 cm2/s, 2.89 × 10−6 cm2/s, and 1.57 × 10−6 cm2/s, respectively. The methanol permeability of 5 wt% PVA/2 wt% PEG/wt.1% Clay is better than of Nafion117 (5.16 × 10−6 cm2/s as reported). The membrane 5 wt% PVA/2 wt% PEG/1% Clay exhibits satisfactory levels of oxidative stability (RW% = 94.09 at 1.32 h), IEC (0.232 meq/g), conductivity (0.00432 S/cm), methanol permeability (1.57 × 10−6 cm2/s), selectivity (3.63 × 10−4 Ss/cm3), and better water uptake properties at fuel cell operating temperature. As a result, it is reasonable to expect that PVA-based modified membranes will outperform NafionTM membranes in the future.

Enhancing the inherent NIR photoluminescence in SrLaLiTeO6 through Cr3+-Yb3+ co-substitution for high performance pc-LEDs.

Until now, double perovskite tellurates have not been reported to exhibit inherent NIR photoluminescence. Therefore, the current study's revelation of inherent NIR luminescence in SrLaLiTeO6 double perovskite centered at 970 nm under 340 nm excitation is particularly intriguing. This phenomenon is attributed to the photoluminescence of Te4+ ions. This study also examines the NIR luminescence of Cr3+-Yb3+ co-doped SrLaLiTeO6. The host and SrLaLiTeO6:3%Cr3+, y%Yb3+ (y = 1, 2, 4, 6, 8, 10 mol%) were synthesized using the solid-state ceramic route. The successful incorporation of Cr3+ and Yb3+ ions into the host lattice was confirmed through XRD, Raman, and diffuse reflectance spectral analyses. Under 270 nm excitation, the photoluminescence (PL) of SrLaLiTeO6:Cr3+ exhibits a blueshift of the PL band to 965 nm due to the 4T2(4F) → 4A2g(4F) emission component of Cr3+ ions. The excited-state lifetime of SrLaLiTeO6:0.5%Cr3+ was measured at 36 μs, but this decreased to 26 μs as the Cr3+ concentration reached 10 mol%, primarily due to the enhancement of non-radiative energy transfer between Cr3+ ions. Incorporating Yb3+ into the system results in additional spectral lines with an enhanced intensity in the range of 970 nm to 1125 nm when excited at 270 nm. These emission lines correspond to the 2F5/2 → 2F7/2 transitions of Yb3+ ions, indicating an efficient energy transfer from Cr3+ to Yb3+. Furthermore, the study also reveals that Yb3+ emission is observed even without Cr3+ ions in SrLaLiTeO6 under 340 nm excitation, suggesting the possibility of energy transfer from the host to Yb3+ ions. The thermal stability and crystal field parameters of the synthesized phosphors are also explained in detail. To explore the potential of these phosphors in practical applications, phosphor-converted NIR LEDs were fabricated using SrLaLiTeO6, SrLaLiTeO6:3% Cr3+, and SrLaLiTeO6:3% Cr3+, 1%Yb3+.

Intriguing properties of graphite/polysiloxane composite-based pencil electrodes

Pencil leads can be considered well-defined and cheap graphite electrodes for a wide range of electrochemistry applications. These electrodes display many intriguing properties; however, the origin of these properties is not clear. Using various analytical approaches applied to two different commercially available Tombow (TO) and Staedtler (ST) pencils we reveal a causal relationship between the unique properties of pencils and their graphite/polysiloxane composite. We explore the impact of chloroform etching on chemical composition changes, thermal stability and electrochemical parameters of pencils. Using a combination of X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS/MS) various polydimethylsiloxanes in composites are revealed. The polysiloxane species leave into the chloroform solvent during the etching resulting in a significant decrease of their content within the electrodes. Differential scanning calorimetry (DSC) data, corroborated by gravimetric measurements, provide additional proof of the presence of composite structures in ST and TO pencils, showing glass transition temperatures at around 76 °C and 81 °C. The main difference between the TO and ST electrodes is the content and composition of the polysiloxanes within the graphite matrix. ST composites have significantly higher polymer content (∼ 30 %) with traces of Na and S impurities compared to TO ones (∼ 14 %) free of contaminations. Furthermore, mainly cyclic nanostructures appear in chloroform extracts of ST composites whereas rather chain-like clusters are liberated out of the TO counterparts. Complementary electrochemical experiments using cyclic voltammetry (CV), impedance spectroscopy (EIS) and the less known elimination voltammetry with linear scan (EVLS) reflect the performance superiority of TO electrodes with much lower polysiloxane content and free of impurities. High conductivity, low capacitive current along with favoured charge carrier transfer all promise a wide range of technological applications for the TO pencil material.

Preparation and characterization of polymer blend electrolyte membranes based on lithium acetate‐complexed carboxymethyl cellulose (CMC) and carboxymethyl chitosan (CMCh) blend

AbstractThis work aimed to prepare solid polymer blend electrolytes based on carboxymethyl cellulose (CMC) and carboxymethyl chitosan (CMCh) complexed with lithium acetate (LiCH3COO) for lithium‐ion batteries application. The solid polymer blend electrolytes of LiCH3COO‐complexed CMC/CMCh (50/50) polymer blend electrolyte were prepared by using the casting solution technique, where various weight percentages of LiCH3COO were mixed into CMC/CMCh (50/50) blend as host polymer. Solid polymer blend electrolytes of CMC/CMCh + 30wt% LiCH3COO had the highest ionic conductivity as much as 2.24 × 10−5 S cm−1 among others. The CMC/CMCh blend (50/50) + 30wt% LiCH3COO degraded at temperature interval 256–473°C. Linear sweep voltammetry method shows that CMC/CMCh (50/50) + 30wt% LiCH3COO reached a decomposition voltage around 2.54 V, while CMC/CMCh (50/50) + 10wt% LiCH3COO was decomposed at a lower voltage around 1.55 V. Based on the transference number measurement appeared that the initial and final current values of 0.84 for the CMC/CMCh (50/50) + 30wt% LiCH3COO is higher than that of the CMC/CMCh (50/50) + 10wt% LiCH3COO (0.8). Based on the results obtained, it can be concluded that the CMC/CMCh blend (50/50) + 30wt% LiCH3COO meets the minimum requirements for the main parameters of ion conductivity and thermal stability as a solid electrolyte polymer membrane but needs improvement and attention to its mechanical properties.Highlights CMC and carboxymethyl chitosan (CMCh) have polar groups for ionic conduction. The CMC/CMCh blend (50/50) + 30wt% LiCH3COO has good ionic conductivity of 2.24 × 10−5 S cm−1. The CMC/CMCh blend (50/50) + 30wt% LiCH3COO has high thermal stability 256–473°C. The CMC/CMCh blend (50/50) + 30wt% LiCH3COO has high decomposition voltage around 2.54 V. The CMC/CMCh blend (50/50) + 30wt% LiCH3COO has higher transference number (0.84).

Studies of luminescence traits and Judd-Ofelt analysis of Sm3+ activated oxyfluoride glasses

Novel Sm3+ activated oxyfluoride glass was synthesized via the melt-quenching approach with subsequent heat treatment. The X-ray diffraction measurement discloses the amorphous nature of prepared glasses. And, FTIR illustrates the molar surplus of Bi2O3 raises the network connectivity by creating bridging oxygen sites in the structure. The Judd-Ofelt (J-O) intensity parameters exhibit Ω4>Ω2>Ω6 trend, witnessing the rigidity of the glass structure and ionic bonding between Sm3+ ions and surrounding ligands. The 4G5/2 → 6H7/2 transition of Sm3+ is the most applicable for reddish-orange lasers due to their higher values of radiative transition probability, branching ratio, and stimulated emission cross-section. The optimum emission intensity is obtained with 30 mol% Bi2O3 and the corresponding decay time is 1.40 ms. Additionally, the F30 glass sample was lit in a reddish-orange region having a CCT value of 1689 K. The thermal luminescence quenching of the prepared glass was studied and the thermal stability parameters activation energy was estimated. Further, the contactless optical thermometry capability of the glass sample was explored within the range of 303 K–603 K using the luminescence intensity ratio (LIR) technique. Thus, the above studies on the glass sample suggest that it can be used as an active medium in lasers, contactless optical temperature sensing, and high-energy scintillator applications.

Criticality and topological classes of neutral Gauss–Bonnet AdS black holes in 5D

This work investigates the thermodynamics, phase transition, and topological classes of Neutral Gauss–Bonnet (GB) AdS black holes (BHs) in 5D. We obtain equations for several thermodynamic quantities for the Neutral GB of AdS BHs by using the well-known properties of BH thermodynamics. We find thermal stability and other significant thermodynamical parameters that assist us study stability and criticality. Thermodynamic features of Neutral GB AdS BHs are graphically explored by utilizing (Cp), (T−S), (P−rh), and G, volume expansivity (β), isothermal compressibility (κ). Second-order phase transitions, like Cp−S illustrates the divergence behavior. In addition, the swallow tail behavior finds the stability and instability of small black holes (SBH), intermediate black holes (IBH), and large black holes (LBH). Also, our investigation focuses on analyzing the topology of thermodynamic critical points and calculating their respective topological charges within the canonical and grand canonical ensembles. This analysis allows us to discuss the ensemble dependence of the Neutral GB-AdS BH exists.

Triptycene Based 3D Covalent Organic Frameworks (COFs)—An Emerging Class of 3D Structures

Covalent Organic Frameworks (COFs) are a newly emerged class of porous materials consisting of organic building blocks linked by strong covalent bonds. The physical and chemical properties of COFs, i.e., modularity, porosity, well-developed specific surface area, crystallinity, and chemical-thermal stability, make them a good application material, especially in the aspects of adsorption and gas separation. The organic compositions of their building blocks also render them with biocompatible properties; therefore, they also have potential in biomedical applications. Depending on the symmetry of the building blocks, COF materials form two-dimensional (2D COF) or three-dimensional (3D COF) crystal structures. 3D COF structures have a higher specific surface area, they are much lighter due to their low density, and they have a larger volume than 2D COF crystals, but, unlike the latter, 3D COF crystals are less frequently obtained and studied. Selecting and obtaining suitable building blocks to form a stable 3D COF crystal structure is challenging and therefore of interest to the chemical community. Triptycene, due to its 3D structure, is a versatile building block for the synthesis of 3D COFs. Polymeric materials containing triptycene fragments show good thermal stability parameters and have a very well-developed surface area. They often tend to be characterized by more than one type of porosity and exhibit impressive gas adsorption properties. The introduction of a triptycene backbone into the structure of 3D COFs is a relatively new procedure, the results of which only began to be published in 2020. Triptycene-based 3D COFs show interesting physicochemical properties, i.e., high physical stability and high specific surface area. In addition, they have variable porosities with different pore diameters, capable of adsorbing both gases and large biological molecules. These promising parameters, guaranteed by the addition of a triptycene backbone to the 3D structure of COFs, may create new opportunities for the application of such materials in many industrial and biomedical areas. This review aims to draw attention to the symmetry of the building blocks used for COF synthesis. In particular, we discussed triptycene as a building block for the synthesis of 3D COFs and we present the latest results in this area.

Growth and Characterization of Organic 2-Chloro 5-Nitroaniline Crystal Using the Vertical Bridgman Technique

In this article, we discuss the preparation of organic 2-chloro-5 nitroaniline (2C5NA) crystals and their different kinds of physical, chemical, and mechanical properties. The vertical Bridgman approach was used to effectively produce the bulk organic 2C5NA crystal. To produce a good-quality bulk crystal, the shape, dimensions, and cone angle of the ampoule were optimized. Also, the temperature profile was set for the 2C5NA crystal. The growth atmosphere and the lowering rate were identified to obtain a homogeneous mixture of the compounds and initiate the nucleation process. Single-crystal X-ray diffraction (XRD), powder XRD, proton Fourier transform nuclear magnetic resonance (FT-NMR), and Fourier transform infrared investigations were used to confirm the crystal structure, molecular structure, and presence of functional groups in the formed crystal. The formed crystal has a monoclinic crystal structure with the space group P21/c, according to single-crystal XRD analysis. The thermal stability and kinetic parameters were examined using thermogravimetric analysis and differential thermal curves. From dielectric analysis, the electrical conductivity and dielectric behavior of 2C5NA were investigated with variations in frequency and temperature. The organic 2-chloro-5-nitroaniline crystal demonstrates that the indentation size effect is observed in the Vickers micro-hardness test, which was also carried out.

Protection Function and Mechanism of Rosemary (Rosmarinus officinalis L.) Extract on the Thermal Oxidative Stability of Vegetable Oils.

Rosemary (Rosmarinus officinalis L.) extract (RE) is one of the most efficient natural antioxidants and can significantly inhibit oil oxidation during storage or heating. The present study determined the protective capacity and mechanism of RE on the thermal oxidative stability of different vegetable oils by adding RE (70% carnosic acid) to five types of vegetable oils (soybean oil, rapeseed oil, cottonseed oil, rice bran oil, and camellia oil) and measuring the physicochemical indices (fatty acid composition, tocopherol content, total phenolic content, and free radical scavenging capacity), induction period, and thermal oxidative kinetic parameters. The relationships between the antioxidant capacity and thermal stability parameters were determined. The results show that, compared with artificial antioxidants, RE significantly increased the free radical scavenging capacity, induction period, and activation energy (Ea) of thermal oxidation, decreasing the thermal oxidation reaction rate (k) of all vegetable oils, especially rice bran oil. A Spearman correlation analysis showed that the induction period (IP) and Ea showed a significant positive correlation, the combination of which effectively reflected the efficiency of antioxidants and explained the inhibition mechanism of RE towards oil thermal oxidation.

The effect of aligning graphene‐oxide nanoplatelets on moisture absorption and thermal stability of polymeric nanocomposites

AbstractThis article investigates the effect of aligning graphene‐oxide nanoplatelets (GONPs) on the moisture absorption and thermal stability of polymeric nanocomposites. Various nanocomposite specimens were fabricated using different GONP contents to improve water uptake resistance and thermal stability by aligning GONPs using an AC electric field during manufacturing. The results showed that aligning 0.3 wt% GONPs resulted in the most significant improvements, with the reductions of 76% and 54% observed in the water uptake of nanocomposites at the initial and saturation stages, respectively. The thermal stability of the nanocomposite specimens was also investigated using thermogravimetric analysis, in which nanocomposites containing 0.3 wt% randomly dispersed GONPs demonstrated improved performance compared with the neat epoxy specimen. However, aligning GONPs resulted in a marginal effect on the thermal stability parameters of nanocomposites. Moreover, Fourier transform infrared spectroscopy was conducted to investigate the chemical nature and hydrophilicity of the specimens. In addition, the freeze‐fractured surfaces of the neat and nanocomposite specimens were investigated using scanning electron microscopy. The results indicated the role of nanoparticle alignment in enhancing the performance of nanocomposites under hygrothermal conditions in terms of water uptake, which is of high importance in the marine industry.