Showing papers on "Thermal stability published in 2015"
TL;DR: Three-dimensional porous crystalline polyimide covalent organic frameworks (termed PI-COFs) have been synthesized and show high thermal stability and surface area and high loading and good release control for drug delivery applications.
Abstract: Three-dimensional porous crystalline polyimide covalent organic frameworks (termed PI-COFs) have been synthesized. These PI-COFs feature non- or interpenetrated structures that can be obtained by choosing tetrahedral building units of different sizes. Both PI-COFs show high thermal stability (>450 °C) and surface area (up to 2403 m2 g–1). They also show high loading and good release control for drug delivery applications.
730 citations
Posted Content•
TL;DR: Analysis shows that Cs-based devices are as efficient as, and more stable than methylammonium-based ones, after aging, as well as under constant illumination, and under electron beam irradiation.
Abstract: Direct comparison between perovskite-structured hybrid organic-inorganic - methyl ammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide (CsPbBr3), allows identifying possible fundamental differences in their structural, thermal and electronic characteristics. Both materials possess a similar direct optical band-gap, but CsPbBr3 demonstrates a higher thermal stability than MAPbBr3. In order to compare device properties we fabricated solar cells, with similarly synthesized MAPbBr3 or CsPbBr3, over mesoporous titania scaffolds. Both cell types demonstrated comparable photovoltaic performances under AM1.5 illumination, reaching power conversion efficiencies of ~6 % with a poly-aryl amine-based derivative as hole transport material. Further analysis shows that Cs-based devices are as efficient as, and more stable than methyl ammonium-based ones, after aging (storing the cells for 2 weeks in a dry (relative humidity 15-20%) air atmosphere in the dark) for 2 weeks, under constant illumination (at maximum power), and under electron beam irradiation.
683 citations
TL;DR: Improved mechanical properties of nanocomposites is due to the uniform dispersion of functionalised graphene and strong interfacial bonding between modified graphene and epoxy resin as confirmed by microscopy observations.
Abstract: Thermally reduced graphene nanoplatelets were covalently functionalised via Bingel reaction to improve their dispersion and interfacial bonding with an epoxy resin. Functionalised graphene were characterized by microscopic, thermal and spectroscopic techniques. Thermal analysis of functionalised graphene revealed a significantly higher thermal stability compared to graphene oxide. Inclusion of only 0.1 wt% of functionalised graphene in an epoxy resin showed 22% increase in flexural strength and 18% improvement in storage modulus. The improved mechanical properties of nanocomposites is due to the uniform dispersion of functionalised graphene and strong interfacial bonding between modified graphene and epoxy resin as confirmed by microscopy observations.
459 citations
TL;DR: In this article, a set of complementary advanced thermal techniques, rarely applied in polysaccharides characterizations, were used to reveal thermal events and identify degradation products as a function of the temperature: three main steps in chitosan (N deacetylation degree, DD = 78%) thermal degradation were highlighted and mechanism proposed.
340 citations
TL;DR: The rational design of template-free nanosized FAU zeolites with exceptional properties, including extremely small crystallites with a narrow particle size distribution, high crystalline yields and excellent thermal stability leading to superior catalytic performance in the dealkylation of a bulky molecule.
Abstract: Nanosized faujasite (FAU) crystals have great potential as catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewable feedstocks in oil refining, petrochemistry and fine chemistry. Here, we report the rational design of template-free nanosized FAU zeolites with exceptional properties, including extremely small crystallites (10-15 nm) with a narrow particle size distribution, high crystalline yields (above 80%), micropore volumes (0.30 cm(3) g(-1)) comparable to their conventional counterparts (micrometre-sized crystals), Si/Al ratios adjustable between 1.1 and 2.1 (zeolites X or Y) and excellent thermal stability leading to superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene, probing sites mostly located on the external surface of the nanosized crystals. Another important feature is their excellent colloidal stability, which facilitates a uniform dispersion on supports for applications in catalysis, sorption and thin-to-thick coatings.
340 citations
TL;DR: In this paper, a series of high thermallyconductive shape-stabilized phase change materials (ss-PCMs) were tailored by blending PEG with AgNPsdecorated diatomite.
Abstract: Ag nanoparticles (AgNPs) are a promising additive because they can enhance the thermal conductivity of organic phase change materials. In this paper, a series of high thermally-conductive shape-stabilized phase change materials (ss-PCMs) were tailored by blending PEG with AgNP-decorated diatomite. In order to enlarge its pore size and specific surface area and make it a suitable PEG carrier, the effect of alkali leaching on the microstructure of diatomite was studied. While PEG melted during phase transformation, the maximum load of PEG could reach 63 wt%, which was 31% higher than that of the raw diatomite. Spherical-shaped crystalline AgNPs with a diameter range of 3–10 nm were uniformly decorated onto diatomite. The XPS results for this material proved that the valence state of silver in the PEG/diatomite PCM was mainly zero. The phase change enthalpy of the PEG/diatomite/Ag PCM reached 111.3 J g−1, and the thermal conductivity of the PEG/diatomite PCM containing 7.2 wt% Ag was 0.82 W m−1 K−1, which was 127% higher than that of the PEG/diatomite composite. The reduced melting and freezing periods indirectly proved that heat transfer in the composite material during the heat storage and release process was enhanced through the thermal conductivity improvement. The composite PCM was thermally and chemically stable even after 200 cycles of melting and freezing. This indicated that the resulting composite PCMs were promising candidate materials for building applications due to their large latent heat, suitable phase change temperature, excellent chemical compatibility, improved supercooling extent, and high thermal stability.
282 citations
TL;DR: Thermal stability of hybrid solar cells containing spiro-OMeTAD as hole-transporting layer is investigated and suppression of the crystal growth in the holes is demonstrated to be a viable tactic to achieve a significant increase in the solar cell resistance to thermal stress and improve the overall lifetime of the device.
Abstract: Thermal stability of hybrid solar cells containing spiro-OMeTAD as hole-transporting layer is investigated. It is demonstrated that fully symmetrical spiro-OMeTAD is prone to crystallization, and growth of large crystalline domains in the hole-transporting layer is one of the causes of solar cell degradation at elevated temperatures, as crystallization of the material inside the pores or on the interface affects the contact between the absorber and the hole transport. Suppression of the crystal growth in the hole-transporting layer is demonstrated to be a viable tactic to achieve a significant increase in the solar cell resistance to thermal stress and improve the overall lifetime of the device. Findings described in this publication could be applicable to hybrid solar cell research as a number of well-performing architectures rely heavily upon doped spiro-OMeTAD as hole-transporting material.
271 citations
TL;DR: It is demonstrated that with the increase in Mn content and decrease in Ni content, the cycling stability of LiNi(0.1+x)O2 to a cutoff charge voltage of 4.5 V is significantly improved and the thermal stability of the Ni-rich cathode is also remarkably enhanced.
Abstract: Ni-rich layered oxides (Ni content >60%) are promising cathode candidates for Li-ion batteries because of their high discharge capacity, high energy density, and low cost. However, fast capacity fading, poor thermal stability, and sensitivity to the ambient moisture still plague their mass application. In this work, we systematically investigate the effects of Mn content on the structure, morphology, electrochemical performance, and thermal stability of the Ni-rich cathode materials LiNi0.8–xCo0.1Mn0.1+xO2 (0.0 ≤ x ≤ 0.08). It is demonstrated that with the increase in Mn content and decrease in Ni content, the cycling stability of LiNi0.8–xCo0.1Mn0.1+xO2 to a cutoff charge voltage of 4.5 V is significantly improved. The high-Mn-content electrode LiNi0.72Co0.10Mn0.18O2 shows a capacity retention of 85.7% after 100 cycles at a 0.2 C rate at room temperature, much higher than those of the lower Mn-content samples LiNi0.80Co0.10Mn0.10O2 (64.0%) and LiNi0.76Co0.10Mn0.14O2 (72.9%). The improved capacity retenti...
237 citations
TL;DR: In this paper, high-temperature properties of boron nitride platelets were systematically evaluated through TGA in combination with differential scanning calorimetry (DSC) X-Ray Diffraction (XRD) studies confirmed the hexagonal graphitic-like structure of the material, while Fourier-Transform Infrared Spectroscopy (FT-IR) indicated the active vibration modes related to the B-N bond.
214 citations
TL;DR: An atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP, finding that decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorus like skeleton remains.
Abstract: With a semiconducting band gap and high charge carrier mobility, two-dimensional (2D) black phosphorus (BP)—often referred to as phosphorene—holds significant promise for next generation electronics and optoelectronics. However, as a 2D material, it possesses a higher surface area to volume ratio than bulk BP, suggesting that its chemical and thermal stability will be modified. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP. From in situ scanning/transmission electron microscopy, decomposition of 2D BP is observed to occur at ∼400 °C in vacuum, in contrast to the 550 °C bulk BP sublimation temperature. This decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorus like skeleton remains. In situ electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss near-edge structure changes provide quantitative insight into this chemical transformation process.
209 citations
TL;DR: It is demonstrated that the chia mucilage hydrocolloid has important properties and potential as an edible film, or coating.
TL;DR: The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability.
Abstract: Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.
TL;DR: In this paper, the incorporation of the as-prepared nanosilica/graphene oxide (m-SGO) hybrid into epoxy (EP) resin not only obviously increases the flame retardancy, mechanical, and thermal stability properties, but also endows EP resin with high thermal conductivity, low dielectric loss, and high dielectoric constant.
Abstract: Graphene is regarded as a prominent multi-functional flame retardant for use in halogen-free flame retardant polymers with simultaneously improved integrated properties and special functionalities. However, its flame retardant efficiency is not impressive enough due to the weak resistance to thermo-oxidative decomposition. In order to overcome this problem, the surface of graphene oxide was covered with large amounts of non-flammable silicas through a sol–gel and surface treatment process, and then used to modify the epoxy (EP) resin. Results show that the incorporation of the as-prepared nanosilica/graphene oxide (m-SGO) hybrid into EP resin not only obviously increases the flame retardancy, mechanical, and thermal stability properties, but also endows EP resin with high thermal conductivity, low dielectric loss, and high dielectric constant. Specifically, the peaks of the heat release rate and total heat release of the modified EP resin with 1.5% m-SGO decrease by 39% and 10% of those of neat EP resin, respectively. These attractive features of m-SGO/EP nanocomposites are attributed to the unique structure and high resistance to oxidative degradation of m-SGO as well as its good interactions with EP resin. The investigation provides a new approach for the preparation of novel core–shell flame retardants through surface wrapping with other flame retardants on SGO and related high performance flame retardant resins.
TL;DR: This is a unique example of thermally and chemically stable conjugated polymers with hollow nanostructures and optoelectronic properties, promising the development of functional hollow g-C3N4 nanocomposites by chemical modifications like doping, surface grafting, and coupling with other inorganic/polymeric semiconductors with the aid of thermal treatment at high temperatures.
Abstract: Hollow-structured g-C3N4 polymers with a high thermal stability up to 550 °C and an enhanced photocatalytic activity have been developed by post-annealing treatment, which effectively modifies the textural, crystal, and electronic properties of the g-C3N4 semiconductors without extra chemical assistance. This is a unique example of thermally and chemically stable conjugated polymers with hollow nanostructures and optoelectronic properties, promising the development of functional hollow g-C3N4 nanocomposites by chemical modifications like doping, surface grafting, and coupling with other inorganic/polymeric semiconductors with the aid of thermal treatment at high temperatures.
TL;DR: In this paper, the authors used FT-IR spectra to obtain information about the nanoparticle-matrix interactions, including morphology, structure, thermal stability, water absorption, biodegradability, cytocompatibility, barrier, mechanical, viscoelastic, antibacterial, and wound healing properties of the films have been analyzed.
TL;DR: In this article, the effect of the substrate temperature (Tsubstrate) on glasses of three organic molecules used as semiconductors was investigated with spectroscopic ellipsometry, and it was shown that the dependence of molecular orientation upon substrate temperature is remarkably similar and nearly independent of molecular length.
Abstract: Physical vapor deposition is commonly used to prepare organic glasses that serve as the active layers in light-emitting diodes, photovoltaics, and other devices. Recent work has shown that orienting the molecules in such organic semiconductors can significantly enhance device performance. We apply a high-throughput characterization scheme to investigate the effect of the substrate temperature (Tsubstrate) on glasses of three organic molecules used as semiconductors. The optical and material properties are evaluated with spectroscopic ellipsometry. We find that molecular orientation in these glasses is continuously tunable and controlled by Tsubstrate/Tg, where Tg is the glass transition temperature. All three molecules can produce highly anisotropic glasses; the dependence of molecular orientation upon substrate temperature is remarkably similar and nearly independent of molecular length. All three compounds form “stable glasses” with high density and thermal stability, and have properties similar to stable glasses prepared from model glass formers. Simulations reproduce the experimental trends and explain molecular orientation in the deposited glasses in terms of the surface properties of the equilibrium liquid. By showing that organic semiconductors form stable glasses, these results provide an avenue for systematic performance optimization of active layers in organic electronics.
TL;DR: It is shown that the enzyme lipase from Rhizopus oryzae exhibits exceptionally high thermal stability and high solvent tolerance and even increased activity in acetone when immobilized onto a graphene oxide nanosupport prepared by Staudenmaier and Brodie methods.
Abstract: The thermal and solvent tolerance of enzymes is highly important for their industrial use. We show here that the enzyme lipase from Rhizopus oryzae exhibits exceptionally high thermal stability and high solvent tolerance and even increased activity in acetone when immobilized onto a graphene oxide (GO) nanosupport prepared by Staudenmaier and Brodie methods. We studied various forms of immobilization of the enzyme: by physical adsorption, covalent attachment, and additional crosslinking. The activity recovery was shown to be dependent on the support type, enzyme loading and immobilization procedure. Covalently immobilized lipase showed significantly better resistance to heat inactivation (the activity recovery was 65% at 70 °C) in comparison with the soluble counterpart (the activity recovery was 65% at 40 °C). Physically adsorbed lipase achieved over 100% of the initial activity in a series of organic solvents. These findings, showing enhanced thermal stability and solvent tolerance of graphene oxide immobilized enzyme, will have a profound impact on practical industrial scale uses of enzymes for the conversion of lipids into fuels.
TL;DR: In this article, a novel kind of graphene oxide-modified poly(melamine-formaldehyde) (PMF) microcapsule containing phase change material (microPCM) n-dodecanol was prepared by in situ polymerization.
Abstract: A novel kind of graphene oxide-modified poly(melamine-formaldehyde) (PMF) microcapsule containing phase change material (microPCM) n-dodecanol was prepared by in situ polymerization. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to study the chemical structure of graphene oxide (GO) and microPCMs, respectively. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the morphology of GO and microPCMs, respectively. The thermal properties of microPCMs were studied by differential scanning calorimetry (DSC), thermal constant analysis (TCA) and thermal cycling tests. The FTIR and XRD results indicate that the phase change material n-dodecanol is encapsulated in the GO/PMF composite shell, and there is no chemical reaction between them. The SEM results show that the prepared GO-modified PMF microPCMs are spherical particles with a smooth surface. The DSC results indicate that the phase change temperature and the latent heat of microPCMs with 1 wt% of GO are 26.40 °C and 125.2 J g−1, respectively. The thermal conductivity of GO/microPCMs with 4 wt% GO increases by 66.29%, compared with that of microPCMs without GO according to the TCA results. Moreover, the thermal cycling tests show that the prepared microPCMs possess a good thermal stability. The GO-modified PMF microPCMs are sure to have great potential applications in thermal energy storage.
TL;DR: Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability and changes in ΔS and ΔH of deactivation were found for the immobilized enzyme.
TL;DR: In this paper, the hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoretic deposition process to obtain uniform bioactive coating with improved mechanical strength and favorable corrosion stability.
TL;DR: In this paper, Lignin nanoparticles (LNPs) were obtained through precipitation from an ethylene glycol solution by using diluteacidic aqueous solutions, and the results indicated that LNPs could also effectively absorb ultraviolet spectrum and improve the water sensitivity of WG bionanocomposites.
TL;DR: Graphene nanoplatelets (GNP)/silicone rubber composites were prepared with the assistance of the Flacktek SpeedMixer as discussed by the authors, and the results showed that the GNP present a homogeneous dispersion in silicone rubber and the thermal conductivity of composites exhibits improving from 0.16 to 0.26 W/m·K (an increase of 53.1%).
TL;DR: In this article, a facile approach to fabricate graphene nanoplatelets (GNPs)/epoxy composites with a novel blend method was reported, and the influence of GNPs on the thermal and electrical properties was investigated.
Abstract: We reported a facile approach to fabricate graphene nanoplatelets (GNPs)/epoxy composites with a novel blend method. The influence of GNPs on the thermal and electrical properties was investigated. Compounds with different GNPs content (0-8 wt%) were mixed with a Flacktek speedmixer at a speed of 3000 rpm for 5 min. The thermal conductivity of the epoxy composites with 8 wt% GNPs was 1.181 W/m K, which is increased by 627% compared with those of the neat epoxy. It is found that the thermal stability and electrical property also have a certain degree of improvement. Scanning electron microscopy images demonstrate that the structures of the composites have a closed relationship with their properties. In addition, the incorporation of GNPs in epoxy matrix indicated excellent Vickers hardness at the low weight fractions of GNPs. POLYM. COMPOS. 36:556-565, 2015. (c) 2014 Society of Plastics Engineers
TL;DR: In this paper, an in-depth comparative study of poly(propylene-2,5-furan dicarboxylate) (PPF) is performed.
TL;DR: In this paper, a new paraffin/expanded vermiculite composite phase change material (PCM) was tailor-made as aggregate for developing lightweight thermal energy storage cement-based composites (LW-TESCCs).
Journal Article•
TL;DR: It is shown here that molecular orientation in organic glasses is primarily controlled by the substrate temperature during deposition, suggesting that the performance of almost any device based upon amorphous organic materials might be systematically optimized by this route.
TL;DR: The design of these compounds was based on the assumption that by the combination of varying oxadiazole rings, it would be possible to profit from the positive aspects of each of the components to produce good thermal stability, density, and, in some cases, energetic performance.
Abstract: Salts generated from linked 1,2,4-oxadiazole/1,2,5-oxadiazole precursors exhibit good to excellent thermal stability, density, and, in some cases, energetic performance. The design of these compounds was based on the assumption that by the combination of varying oxadiazole rings, it would be possible to profit from the positive aspects of each of the components. All of the new compounds were fully characterized by elemental analysis, IR spectroscopy, 1H, 13C, and (in some cases) 15N NMR spectroscopy, and thermal analysis (DSC). The structures of 2–3 and 5-1⋅5 H2O were confirmed by single-crystal X-ray analysis. Theoretical performance calculations were carried out by using Gaussian 03 (Revision D.01). Compound 2-3, with its good density (1.85 g cm−3), acceptable sensitivity (14 J, 160 N), and superior detonation pressure (37.4 GPa) and velocity (9046 m s−1), exhibits performance properties superior to those of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX).
TL;DR: In this paper, a shape-stabilized phase change material (PCM) was developed by impregnation of hydrated salts into expanded graphite (EG) and further coated with paraffin wax.
TL;DR: In this paper, a novel formulation of o/w emulsion stabilized using nanoparticle-surfactant polymer system is investigated for the formulation of thermally stable Pickering emulsion.
TL;DR: In this paper, a reaction flame retardant hexa-(phosphite-hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HPHPCP) was synthesized by hexachlorocyclotri phosphazenes, diethyl phosphite and p -hydroxybenzaldehyd.