Differential Thermal Gravimetric Analysis Research Articles

Exploring the impact of pH and temperature on TiC nanopowders syntesized via sol-gel and subsequent crystallization by carbothermal reduction method

In the present study, titanium carbide powders with suitable morphology and nanometer particle size were synthesized by the sol–gel method to investigate the parameters affecting the properties of sol and the final powder. The initial sol was prepared in a four-component system of alkoxide-water-alcohol-citric acid based on the chemical process of sol–gel. The study of sol properties showed that pH was the most important factor in the control of sol conditions and particle size so that at low pHs, due to low concentration of OH− ions and reduced viscosity, it was easier to control the particles size. Accordingly, the results of the Dynamics Light Scattering (DLS) showed that at low pHs, the particles size was below 10 nm. According to the zeta potential diagram and by examining the conditions of sol at different pHs, 4.5 was determined as the optimal pH and to prevent the bonding of particles within the sol, ammonium polycarboxylate dispersant was used. The temperature at which particles were formed was determined using Differential thermal analysis (DTA) and Thermal gravimetric analysis (TG). X-ray diffraction (XRD) patterns showed the presence of a completely amorphous phase at 700 °C. It was also observed that with increasing temperature, TiC crystallization started from 1200 °C and ended at 1400 °C. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) micrographs at 1400 °C showed the completely spherical morphology of particles of nanometer size so that no agglomerate was observed.

Effect of the strength grade of parent concrete on the performance of recycled aggregate treated by cement-fly ash slurry under prolonged soaking duration

The detrimental effects of quarrying natural resources have contributed to large-scale environmental pollution. Utilizing recycled concrete aggregate (RCA) obtained from construction and demolition waste as a replacement for natural aggregates has become an effective solution for environmental sustainability. However, the inevitably diminished characteristics of the adhered mortar and the existence of an additional interfacial transition zone (ITZ) have negatively suppressed the widespread use of these materials in production lines. The present study aims to comprehensively investigate the effects of a cement-fly ash slurry with a mass ratio of 50% of the total weight of RCA on the microstructure and engineering properties of RCA derived from three different parent concretes with strength grades of 20, 30, and 60 MPa. The RCAs were soaked for 24 h, 48 h, and 72 h to evaluate the long-term effects of the pozzolanic slurry. A sequence of laboratory tests was conducted, including mercury intrusion porosimetry (MIP) test, thermal gravimetric–differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and measurements of water absorption and crushing value. The MIP results demonstrated a significant increase in medium capillary and gel pores, and a reduction in large capillary pores in the RCA with an increase in soaking time. TG-DTA results indicated an increase in Ca(OH)2 content during the first 24 h and 48 h of treatment. However, after 72 h of treatment, the Ca(OH)2 content of the treated RCA decreased in all cases. XRD analysis revealed the appearance of a few additional ettringite peaks among the treated RCAs in all cases. SEM images demonstrated the presence of additional hydration products after treatment, which filled the pores and improved the surface texture. Furthermore, after treatment, the crushing value of all treated RCA decreased by 6.0–27.1%, whereas the water absorption decreased by 12.0–30.9% compared to the untreated RCA. Based on several experimental results, the formation of hydration products and the improvement mechanism of RCA from three different parent concretes by slurry treatment with different soaking durations were discussed. In conclusion, a prolonged impregnation time of 72 h yielded a dominant performance, effectively intensifying their inferior properties, regardless of the initial strength grade of parent concrete.

Scouring erosion resistance of nano-marine concrete under the coupled effect of chloride attack and dry - wet cycles

In order to reveal the improving mechanism associated with different types of nanoparticles under the three-factor coupled effects (scour, dry-wet cycles, and Cl- attack), a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2 and nano-Fe3O4 with different content on scouring erosion resistance properties of marine concrete. The micro-structure of the interface transition zone (ITZ) in marine-concrete, as well as the features of hydration products, were characterized using advanced techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG-DSC) analysis, and mercury intrusion porosimetry (MIP). The test results showed that compressive and flexural strength, as well as scouring erosion resistance of marine-concrete were enhanced with the increasing content of nano-SiO2 and nano-Fe3O4 until the threshold limit of 2%, and performance of NSC20 was better than that of NFC20. Under the three-factor coupling, the strength corrosion resistance coefficient of nano-marine concrete was negatively correlated with the scouring erosion rate and the change rate of scouring erosion area, and positively correlated with the resistivity and the Cl- diffusion coefficient with the increase of corrosion age. When the corrosion age reached 70 days, the average scouring erosion rates of NSC20 and NFC20 were decreased 19.86% and 14.43%, respectively, compared with PC. The convective depth of concrete steadily decreased while its diffusive depth increased relative to concrete without scouring. Cl- binding was increased by 28.5%, 27.2%, and 21.4% for PC, NSC20, and NFC20, respectively. The high chemical activity of nano-SiO2 and nano-Fe3O4 promoted the mechanical performance and durability of concrete through improved density and homogeneity of chlorinated products and optimized the structure of the C-S-H/C-F-H gels in ITZ, as indicated by SEM-EDS observation, XRD, and DTG-DSC analysis. The coupling effects resulted in increasing volume of air voids and micro-cracks, as well as weak ITZ due to SA, which hindered scouring resistance development, as indicated by the MIP analysis.

Investigation of electrochemical, optical, and thermal properties via oligomerization of aminophenol monomer containing halogen and nitro groups using two distinct oxidants

In this study, two different oligomers of 2-amino-4-chloro-5-nitrophenol (ACNP) with incorporated halogen atom and nitro groups were synthesized by oxidative oligomerization method using two different oxidants, namely H2O2 and ammonium persulfate (APS). Structural characterizations of the obtained products were elucidated by 1H NMR, 13C NMR, FT-IR, UV–Vis spectroscopy methods. The molecular masses of the oligomers were determined through the utilization of Gel Permeation Chromatography (GPC). The analysis revealed that the Mw values of the oligomers synthesized via the oxidative oligomerization method using H2O2 and APS, denoted as OACNP-1 and OACNP-2 were 4150 Da and 2800 Da, respectively. Using the UV–vis spectrophotometer, the optical band gaps were calculated as 2.64 eV, 1.95 eV and 2.14 eV for ACNP, OACNP-1 and OACNP-2, respectively. Thermal properties of the oligomers were investigated using Thermal Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC). The results demonstrated that OACNP-1 exhibited significantly higher thermal stability when compared to both the monomer and OACNP-2. In addition, Fluorescence Spectroscopic analysis of the oligomers revealed that OACNP-1 emitted blue light at 440 nm when excited with light of a wavelength of 370 nm, exhibiting fluorescent characteristics. Furthermore, the surface properties and morphologies of the oligomers were analyzed with the help of Scanning Electron Microscopy (SEM), revealing a flower-like structure for the oxidative oligomerization product, OACNP-1, in the presence of H2O2. In course of a change in the oxidant, the oligomer, OACNP-2, had rough and spongy surface morphology with some pores.

Synthesis of Functional Isosorbide-Based Polyesters and Polyamides by Passerini Three-Component Polymerization.

A new family of functional isosorbide-based polyesters and polyamides with high glass transition temperature are prepared via Passerini-three component polymerization (P-3CP). To optimize the P-3CP conditions, the influence of the polymerization solvent, temperature, feed ratio on the molar mass of final polymers are investigated. The higher molar mass (up to 10100 g/mol) and yield (>70%) are achieved under mild conditions (30 °C, standard atmosphere). Functional side groups, such as alkenyl, alkynyl and methyl ester, were introduced into polymer structure via P-3CP by using functional isocyanides. The obtained polyesters and polyamides are characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). All polymers are thermal stable and amorphous with variable glass transition temperatures (Tg). The obtained polyester has Tg up to 87.5 °C, while the Tg of polyamides (ISPA-2) is detected to be 97.5 °C depending on the amide bonds in the polymer backbone and the benzene ring side groups. The cytotoxicity is investigated by the CCK-8 assay against mBMSC cells to confirm the biological safety. Overall, this novel strategy provides an efficient approach to produce functional isosorbide-based polyesters and polyamides, which are promising prospect for being applied to biodegradable materials.

Improvement of the structural, dielectric, ferroelectric, and piezoelectric of PbZr0.52Ti0.48O3 nanopowder features for ultrasonic applications

Smart ferroelectric lead zirconate titanate (PbZr0.52Ti0.48O3) was synthesized in the morphotropic phase boundary by a sol-gel auto-combustion strategy. The as-prepared powder was calcined at three different temperatures, 700, 800, and 900 °C for 3 h, each. The tetragonality of the final product increases with the rise of calcination temperature. Thermal gravimetric analysis and differential thermal gravimetric analysis depicted that complete crystallization of PZT was observed at 400 °C. Structural, vibrational, and microstructure studies were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy investigated for grains and elemental analyses and high-resolution transmission electron microscopy (HR-TEM). Results of XRD and HR-TEM were compatible, showing the formation of nanocrystalline powder with coexisting tetragonal and rhombohedral phases. Rietveld refinement of XRD data was carried out using material analysis using diffraction software in order to obtain the lattice constants. For mechanical and electrical measurements, disks were pressed at 10 MPa. The samples were burned out at 500 °C for 1 h and then 1100 °C for 2 h to obtain more dense disks. The surfaces of the disks were coated with silver paste, followed by burning out for almost an hour. Dielectric and piezoelectric characteristics for the fabricated PZT samples were determined in detail. From these analytical techniques and collected data, one can deduce that the sample annealed at 900 °C can be used as an ultrasonic transducer in various metrological applications.

Carboxymethyl chitosan dopamine conjugates: Synthesis and evaluation for intranasal anti Parkinson therapy

With respect to the Parkinson's disease (PD), herein, we aimed at synthetizing and characterizing two novel macromolecular conjugates where dopamine (DA) was linked to N,O-carboxymethyl chitosan or O-carboxymethyl chitosan, being both conjugates obtained from an organic solvent free synthetic procedure. They were characterized by FT-IR, 1H NMR spectroscopies, whereas thermal analysis (including Differential Scanning Calorimetry and Thermal Gravimetric Analysis) revealed good stability of the two conjugates after exposure at temperatures close to 300 °C. Release studies in simulated nasal fluid elucidated that a faster release occurred since O-carboxymethyl chitosan-DA conjugate maybe due to the less steric hindrance exerted by the polymeric moiety. The CMCS-DA conjugates prepared in aqueous medium may self-assembly to form polymeric micelles and/or may form polymeric nanoparticles. TEM and Photon correlation spectroscopy lent support for polymeric nanoparticle formation. Moreover, such CMCS-DA conjugates showed antioxidant activity, as demonstrated by DPPH radical scavenging assay. Finally, cytocompatibility studies with neuroblastoma SH-SY5Y cells showed no cytotoxicity of both conjugates, whereas their uptake increased from 2.5 to 24 h and demonstrated in 40–66 % of cells.

Additive Manufacturing of Single-Layer Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) or proton conducting solid oxide fuel cells (p-SOFCs) have been emerging as a potential low-temperature (400-600oC) fuel cell technology. Generally, the proton conducting ceramic electrolyte materials have a lower activation energy (< 50 eV) and lower electronic conductivity than the conventional oxygen-ion conducting ceramic materials, which are beneficial for improving the fuel cell efficiency and the power output. The additive manufacturing has the potential to transform the manufacturing of PCFCs since it can fabricate both the dense and porous structures with good mechanical and electrochemical properties. In this work, we fabricated single-layer PCFCs through a hybrid of extrusion-based 3D printing utilizing BaZr0.3Ce0.5Y0.15O3-δ and BaZr0.4Ce0.4Y0.1Yb0.1O3-δ as electrolytes, their composite with NiO as anode, and their composite with BaCo0.4Fe0.4Zr0.1Y0.1O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ as cathode. The rheological properties of the printable pastes were investigated in detail with the dynamic light scattering, viscometer, tensiometry, differential scanning calorimetry and thermal gravimetric analysis. Furthermore, the cells are characterized with current-voltage measurements and electrochemical impedance spectroscopy. In addition, other spectroscopic and microscopic measurements (HR-TEM-EELS, SEM-EDX, XPS) were conducted to better understand the mechanisms in the cells. A systematic study was conducted to optimize the sintering temperature for optimal fuel cell performance. Finally, the degradation mechanisms in the cells were investigated in order to improve their stability.Dr. Asghar thanks Academy of Finland (Grant No. 13322738, 13329016, 13352669) for the financial support. Figure 1

Room temperature nematic liquid crystals: Synthesis and characterisation of pentabromophenol and cyanobiphenyl derived rod-shaped molecules

ABSTRACT Calamitic molecules consisting of pentabromophenol tethered to cyanobiphenyl via a flexible alkyl chain were synthesised and characterised for their mesomorphic properties. New chemical structures differing in the length of the spacer (6a–f) were confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopies, and by elemental analysis. Compounds having six, eight, nine and ten methylene units in the spacer show room-temperature nematic liquid crystalline phases and the other derivatives are soft solids. The mesomorphic behaviour and thermal stability of all compounds have been investigated by polarised optical microscopy, differential scanning calorimetry and thermal gravimetric analysis, respectively.

Preparation and properties of double percolated co-continuous PC/PET/MWCNT/GNP engineering polymer blend nanocomposites

This study reports on the preparation and characterization of nanocomposites based on polycarbonate (PC)/poly ethylene terephthalate (PET) blend containing low amounts of hybrid of multiwalled carbon nanotube (MWCNTs) and graphene nanoplates (GNPs) by melt mixing. To use double percolation mechanism, at first a co-continuous polymer blend was prepared and the influence of nanofiller content on morphology, electrical conductivity, rheological and mechanical properties of co-continuous PC/PET blend was investigated. Blend containing 60 wt. % PET showed co-continuous morphology as observed by scanning electron microscopy and it was found that co-continuity remained unchanged by the addition of nanofillers. The direct current (DC) electrical conductivity results showed a low electrical percolation threshold around 0.5 phr. The results obtained from differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) showed an increase in thermal stability and crystallinity of nanocomposites. By increasing nanofiller amount, the storage modulus, loss modulus, and complex viscosity of samples increased as an indication of the strong network formation between nanofillers and polymer chains. The rheological percolation threshold was also found in the range of 2.5–3.5 phr of nanofillers. The tensile measurements results showed that the addition PC to PET increases the tensile strength of PET.

Growth, crystal structure, Hirshfeld surface, spectroscopy studies and DFT calculations of an organic cocrystal of 2-amino-4-hydroxy-6-methylpyrimidine (AHMP) and 2,4-dimethylbenzoic acid (DMBA)

A newly synthesized organic cocrystal (AHMP.DMBA) of 2-amino-4‑hydroxy-6-methylpyrimidine (AHMP) and 2,4-dimethylbenzoic acid (DMBA) was successfully grown by the slow evaporation method. The current report focuses on the molecular structure, vibrational study, thermal analysis and electronic properties of the grown crystal. The crystal structure analysis of AHMP.DMBA cocrystal was done by single crystal X-ray diffraction (SCXRD) technique. The given cocrystal crystallizes in the orthorhombic system space group Pnma. 3D Hirshfeld surface map and its associated 2D fingerprint plots have been generated for understanding the noncovalent interactions which stabilized the crystal pacing. Further, FTIR spectroscopy and B3LYP-D3/6-311++G(d,p) theory have been used to examine the vibrational modes present in the synthesized complex. The observed and simulated 13C and 1H NMR spectral analyses have also supported the structural analysis. The experimental absorption spectra and optical band gap are obtained by UV–Vis absorption spectroscopy and the theoretical electronic spectrum is computed using time dependant density functional theory (TD-DFT) method. The thermal profiles of the given sample have been recorded by thermal gravimetric/differential thermal analysis (TG/DTA). Additionally, the molecular properties i.e., HOMO-LUMO, MEP and non-linear optical parameters are also discussed.

Preparation and evaluation of effective thermal decomposition of tetraamminecopper (II) nitrate carried by graphene oxide

Graphene oxide (GO) was investigated in this paper as a promising catalyst for the effective thermal decomposition of tetraamminecopper (II) nitrate coordination complexes. CuC has been synthesized by doping GO nanoparticles in a one-step method and it demonstrates a uniform deposition of the produced nanocomposites onto the surface of the complex. The kinetics of decomposition and underlying mechanisms of GO on CuC have been studied using a Differential Scanning Calorimetry (DSC) technique and Thermal Gravimetric Analysis (TGA) coupled Fourier-Transform Infrared Spectroscopy (FTIR) technique and relevant theories. Under the effect of GO, the release of heat from the decomposition process is significantly increased from 97.1 J·g-1 to 69.2 J·g-1. Under the effect of GO, the activation energy of the CuC decreased from 94.3 to 82.2 ± 0.5 kJ·mol−1 (for endothermic reaction). The significance of this discovery is due to the reactive sites and great thermal conductivity of the GO. By FTIR analysis, GO affected by the formation of NH3 and N2O; and the decomposition of CuC complex in cooperation with the GO may follow a random scission model (A2) since it highly depends on the edge defects of GO as well as coordination center reactive sites (scission sites). In addition, the combustion behavior of CuC and CuC–GO in the physical mixture with B/KNO3 has been investigated. The results show that the pressure exponent “n” samples (CuC: n = 0.621 vs. CuC–GO: n = 0.703) can be stable and investigated composites are available for successful application as energetic materials.

Preparation and Characterization of a Novel Hyperbranched Polyester Polymers Using A2+B3 Monomers

Abstract Compared to linear analogs, hyperbranched polymers (HBPs) have gotten much attention in the last decade because of their intrinsic globular topologies and distinctive features like low viscosity, high solubility, and a high degree of functionality. In this work, four types of hyperbranched polyester polymer HBPs have been synthesized using the A2+B3 polycondensation methodology. Firstly, the starting material B3 monomer (Pyrimidine-2,4,6-triol) has been synthesized using urea and malonic acid with the presence of sodium Na as the catalyst for the reaction. Secondly, four types of materials (tartaric acid TA, adipic acid AD, maleic acid MA, and phthalic anhydride PA) as A2 monomers were added to the starting material B3 monomer in an oil bath to prepare the four types of HBP. The chemical structure of HBPs was characterized by FTIR, and 1H-NMR. The molecular weight of the prepared HBPs was characterized by gel permeation chromatography GPC, and thermal properties were characterized by differential scanning calorimetry DSC and thermal gravimetric analysis TGA. FTIR results showed that there are new bands, such as C-O-C between A2 and B3 monomers, as indicated by 1H-NMR. In addition, GPC shows that the prepared polymers have a narrow molecular weight distribution with good thermal stability, as indicated by DSC and TGA.

Modified halloysite nanotubes decorated with Ceria for synergistic corrosion inhibition of Polyolefin based smart composite coatings

The deteriorating effect of corrosion can be controlled by applying suitable polymeric-based coatings. In this work, polyolefin based smart composite coatings containing modified halloysite nanotubes decorated with ceria particles were investigated to analyze their anti-corrosion behavior. For this purpose, halloysite nanotubes (Hals) were utilized as nanocarriers which were loaded with sodium dodecyl sulfate (SDS) as a corrosion inhibitor via overnight stirring and vacuum cycling method. The loaded Hals were then modified/decorated with cerium oxide (CeO2) particles by reacting cerium nitrate (Ce (NO3)3.6H2O) and sodium hydroxide (NaOH) which resulted in the formation of CeO2@HAL/SDS. The synthesized modified particles (CeO2@HAL/SDS) were characterized by energy-dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), Fourier-Transform Infrared Spectrometer (FTIR), Thermogravimetric analysis (TGA), and differential thermal gravimetric analysis (DTA), X-ray diffraction analysis (XRD) and UV–vis spectroscopic analysis. TGA analysis results demonstrated that about 32% (w/w) of SDS has been loaded into Hal, and 47% (w/w) of CeO2 has been immobilized on the surface of Hal. UV–Vis analysis results demonstrated the pH-sensitive and time-dependent release behavior of synthesized particles. Furthermore, the modified CeO2@HAL/SDS particles (1 wt%) were reinforced into the polyolefin-based matrix, coated on a polished steel substrate and their electrochemical properties were investigated. The electrochemical impedance spectroscopy (EIS) analysis confirms the promising improvement in the corrosion inhibition performance of polyolefin coatings modified with CeO2@HAL/SDS particles when compared to the polyolefin composite coatings modified with HAL/SDS due to the synergistic corrosion inhibition performance of Ce(OH)3 and Fe-SDS formation at the cathodic and anodic region of steel.

Physical and electrical property studies on sodium (Na+) – Ion conducting Nano–Composite Polymer Electrolyte membranes

Present work reports that Polymer Electrolyte Membranes: [97PEO: 3NaCOOCH3] dispersed with ceramic filler SiO2 have been synthesized using the hot-press casting technique. Ion transport properties have been evaluated in terms of the essential ionic conductivity (σ) and total ionic (tion) / cationic (t+) transference numbers using different ac/dc techniques to evaluate its usefulness in all-solid-state battery applications. Structural/thermal properties have been characterized using X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) techniques. The thermal laminated pouch cell has been fabricated and tested by sandwiching the best optimized NCPE film between MnO2 cathode and Graphite anode. Cyclic Voltammetry study of NCPE film exhibits good electrochemical behaviour and is more suitable for battery fabrication.

Electrical and thermal analysis on Na+ - ion conducting novel blended solid polymer electrolyte membranes

In this study, the hot press method has been used to synthesize a blended solid polymer electrolyte (BSPE), containing poly (ethylene oxide) and polyacrylonitrile (PEO/PAN) matrix complexed with sodium perchlorate (NaClO4) salt. The film with varying salt concentration has been prepared, in which the BSPE OCC (optimum conducting composition) film exhibits the highest ionic conductivity is (σrt) ∼ 2.10 × 10-6 Scm−1 at room temperature. X-ray diffraction (XRD), Impedance Spectroscopy (IS), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) techniques have been adopted for the characterization. These investigations are demonstrated their utility and potential for all-solid-state device applications.

Pyrophyllite clay-derived porous geopolymers for removal of methylene blue from aqueous solutions

This study reports the synthesis and characterization of a porous geopolymer systems based a naturally occurring Moroccan pyrophyllite clay. The contribution of pyrophyllite in geopolymerization reaction was very low, the geopolymer matrix formed was assured by alkaline activation of the metakaolin present in the sample. The pyrophyllite role is forming of disordered and heterogeneous geopolymer promote the pore creation. The structure and morphology of the raw natural clay, calcined meta-pyrophyllite phase and prepared geopolymer samples are characterized by several methods namely, X-ray Diffraction (XRD), 29Si and 27Al magic-angle-spinning nuclear magnetic resonance (MAS NMR) analysis, Fourier Transform Infra-Red (FTIR) spectroscopy, Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA), N2 adsorption/desorption isotherm analysis by the Brunauer-Emmett-Teller (BET) method and Scanning Electron Microscopy (SEM). The specific surface area (SBET) and pore volume (Vp) measured from products utilizing the calcined meta-pyrophyllite precursor (SBET = 86 m2/g and Vp = 0.08 cm3/g) have both increased markedly compared to those values determined using a raw pyrophyllite clay phase (SBET = 30 m2/g and Vp = 0.05 cm3/g). The methylene blue (MB) molecular adsorption experiment realized in water medium exhibited Pseudo Second Order (PSO) rate kinetics and adopted a Langmuir adsorption model. The thermodynamics data shows that the chemisorption is spontaneous, irreversible, and endothermic, with the quantity of MB molecules retained by the porous geopolymer specimen reaching 64.10 mg/g.

Rational Design of Mesoporous Silica (SBA-15)/PF (Phenolic Resin) Nanocomposites by Tuning the Pore Sizes of Mesoporous Silica.

The development of composite materials with functional additives proved to be an effective way to improve or supplement the required properties of polymers. Herein, mesoporous silica (SBA-15) with different pore sizes were used as functional additives to prepare SBA-15/PF (phenolic resin) nanocomposites, which were prepared by in situ polymerization and then, compression molding. The physical properties and structural parameters of SBA-15 with different pore sizes were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The thermal properties of the SBA-15/PF hybrid were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The mechanical, friction, and dynamic mechanical properties of SBA-15/PF nanocomposites were also studied. The results revealed that the pore sizes of SBA-15 have a significant effect on the resulting SBA-15/PF hybrid and SBA-15/PF nanocomposites. The thermal stability of the SBA-15/PF hybrid was dramatically improved in comparison with pure PF. The friction and dynamic mechanical properties of the SBA-15/PF nanocomposites were enhanced significantly. Specifically, the glass transition temperature (Tg) of the nanocomposite increased by 19.0 °C for the SBA-15/PF nanocomposites modified with SBA-15-3. In addition, the nanocomposite exhibited a more stable friction coefficient and a lower wear rate at a high temperature. The enhancement in thermal and frictional properties for the nanocomposites is ascribed to the confinement of the PF chains or chain segments in the mesopores channels.

Coumarin Ketoxime Ester with Electron-Donating Substituents as Photoinitiators and Photosensitizers for Photopolymerization upon UV-Vis LED Irradiation.

High-performance photoinitiators (PIs) are essential for ultraviolet-visible (UV-Vis) light emitting diode (LED) photopolymerization. In this study, a series of coumarin ketoxime esters (COXEs) with electron-donating substituents (tert-butyl, methoxy, dimethylamino and methylthio) were synthesized to study the structure/reactivity/efficiency relationships for substituents for the photoinitiation performance of PIs. The introduction of heteroatom electron-donating substituents leads to a redshift in the COXE absorption of more than 60 nm, which matches the UV-Vis LED emission spectra. The PIs also show acceptable thermal stability via differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The results from real-time Fourier transform infrared (RT-FTIR) measurements indicate that COXEs show an excellent photoinitiation efficiency for free radical polymerization under UV-Vis LED irradiation (365-450 nm); in particular, the conversion efficiency for tri-(propylene glycol) diacrylate (TPGDA) polymerization initiated by COXE-O and COXE-S (4.8 × 10-5 mol·g-1) in 3 s can reach more than 85% under UV-LED irradiation (365, 385 nm). Moreover, the photosensitization of COXEs in the iodonium hexafluorophosphate (Iod-PF6) and hexaarylbiimidazole/N-phenylglycine (BCIM/NPG) systems was investigated via RT-FTIR. As a coinitiator, COXEs show excellent performance in dry film photoresist (DFR) photolithography. This excellent performance of COXEs demonstrates great potential for UV-curing and photoresist applications, providing a new idea for the design of PIs.

Rational design of thermally stable polymorphic layered cathode materials for next generation lithium rechargeable batteries

Classical layered transition metal oxides have remained the preferred cathode materials for commercial lithium-ion batteries. Variation in the transition metal composition and local ordering can greatly affect the structure stability. In classical layered cathodes, high concentrations of electrochemically inert Mn elements usually act as a pillar to stabilize the structure. When excess amount of Li and Mn are present in the layered structure, the capacity of the Li-rich layered oxide (molar ratio of lithium over transition metal is larger than one by design) can exceed that expected from transition metal redox. However, the over lithiation in the classical layered structure results in safety issues, which remains challenging for the commercialization of Li-rich layered oxides. To characterize the safety performance of a series of Li-rich layered cathodes, we utilize differential scanning calorimeter and thermal gravimetric analysis; this is coupled with local structural changes using in situ temperature dependent synchrotron X-ray diffraction and X-ray adsorption spectroscopy. These methods demonstrate that the gradual decrease of the Mn–M (M = Ni, Co, Mn and Li) coordination number directly reduces structural stability and accelerates oxygen release. For safety characterization tests in practice, we evaluate the thermal runaway process through accelerating rate calorimeter in 1.0 Ah pouch cells to confirm this trend. Using the insights obtained in this work, we design a polymorphic composition to improve the thermal stability of Li-rich layered cathode material, which outperforms Ni-rich layered oxides in terms of both electrochemical and safety performances.