Matrix‐Free and Highly Efficient Room‐Temperature Phosphorescence Carbon Dots towards Information Encryption and Decryption

Designing efficient room‐temperature phosphorescence (RTP) carbon dots (C‐dots) without the need of an additional matrix is important for various applications. Herein, matrix‐free and highly efficient C‐dots with yellow‐green RTP emission have been successfully synthesized towards information encryption and decryption. Phytic acid (PA) and triethylenetetramine are used as molecular precursors, and a facile microwave‐assisted heating method is selected as synthesis method. The obtained C‐dots exhibit a maximum phosphorescence emission at around 535 nm under an excitation wavelength of 365 nm and a long average lifetime up to 750 ms (more than 9 s to the naked eye). PA containing six phosphate groups and serving as P source plays a significant role in producing the RTP C‐dots. Furthermore, potential applications of the RTP C‐dots in the field of information encryption and decryption are successfully demonstrated.     

Kinetics study on the dissolution of UO<Subscript>2</Subscript> particles by microwave and conventional heating in 4 mol/L nitric acid

The dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid medium at temperatures of 90–110°C by microwave heating and conventional heating has been investigated, respectively. It is found that the dissolution ratios of UO₂ particles by microwave heating were 10%–40% higher than that by conventional heating. Kinetics research shows that the dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid is controlled by the diffusion control model for microwave heating and by the surface reaction control model for conventional heating. The diffusion control model for the dissolution of UO₂ particles by microwave heating could be explained by the diffuseness on the surface of UO₂ particles.     

Die ermittlung des schmelzpunktes von kristallinen polymeren mittels wärmeflusskalorimetrie (DSC)

Small and imperfect crystals in polymers reorganize during slow heating. This leads to an increase of their melting point T_m. In order to measure the melting point of the original crystals, high heating rates are needed. This is possible with the modern heat-flow-calorimeters, which work with very small samples. The thermal lag of a DSC cell causes a shift of the melting peak by ΔT to higher temperature. From the theory of a heat-flow-calorimeter, it follows that the error ΔT is proportional to the square root of heating rate. heat of fusion and sample mass. Measurements with sharp melting low molecular weight compounds confirm that this square root relation is quantitatively followed. In order to measure the true melting point of the crystals present in a polymer sample, one has to use different high heating rates and constant sample mass. By plotting the melting peak temperatures as a function of the square root of heating rate and linear extrapolation to zero heating rate, the true melting point is found. This method is applied to HDPE, LDPE and some polyamides.     

Comments on multiple publications reporting single heating rate kinetics

This note alerts one to multiple Applied Organometallic Chemistry publications that report the single heating rate kinetics for thermal decomposition of organometallic compounds. It is stressed that the single heating rate approach is known to produce erroneous kinetic parameters. Its use is also against the recommendations of the International Confederation for Thermal Analysis and Calorimetry that advises the multiple heating rate approach to be used instead. Examples of the failure are provided and an appeal is made to the community for adopting the multiple heating rate approach.     

Ammonium polyphosphate-aluminum trihydroxide antagonism in fire retarded butadiene-styrene block copolymer

In this paper the effect of aluminum trihydroxide (Al(OH)₃—ATH) on the surface protection from fire for a styrene butadiene rubber (SBR) provided by ammonium polyphosphate ([NH₄PO₃]_n—APP) is studied.The combustion behaviour is studied by means of Cone Calorimetric tests: a maximum fire retardant effect is observed with 10-12 wt.% of APP. ATH, less effective as fire retardant, has been added at 60 wt.% to reach comparable results as measured by cone calorimetry for 12 wt.% APP.Replacement of ATH in the best performing SBR + 12 wt.% of APP shows an antagonistic effect with as little as 1 wt.% of ATH.The combustion behaviour is explained with the mechanism of interaction between SBR, APP and ATH, in which formation of aluminum phosphates negatively affects the surface protection provided by the ultraphosphate surface coating formed on heating APP in SBR.     

Influence de la vitesse de chauflage sur l'atomisation électrothermique en spectrométrie d'absorption atomique. Applications aux éléments volatils, cadmium et plomb

The advantages of electrothermal atomization by rapid heating (faster than 2000°C s⁻¹) in atomic absorption for the determination of volatile elements are studied. The aim is to control the matrix effects, particularly the very high non-specific absorptions. It is shown that, unlike normal heating, now rapid heating makes it possible to atomize a volatile element without hardly covolatilizing its matrix, as a result of the change in the optimum atomization temperatures.Application examples are given: direct determination of cadmium and lead (atomized respectively at only 900 and 960°C) in sea water and related products. This method is likely to be applicable to other matrices which covolatilize normally with other elements. The mechanisms of atom formation in rapid heating are also investigated.     

Influence of the temperature on polyelectrolyte microcapsules: Light scattering and confocal microscopy data

The influence of heating on polyelectrolyte (PE) microcapsules consisting of an even or uneven number of alternating layers of poly(allylamine) and poly(styrenesulfonate) is investigated by the light scattering and confocal microscopy techniques. In the formation of PE microcapsules, CaCO₃ microspherulites are used as “core” dispersed particles. It is established that the capsules decrease in size with increasing temperature and time of heating, irrespective of whether they consist of an even or uneven number of layers. The sensitivity of PE microcapsules to heat is estimated in terms of the activation energy of changes in parameters of their initial structure on heating. It is shown that PE microcapsules consisting of an uneven number of layers are more sensitive to heating as compared to those consisting of an even number of layers. A plausible mechanism is proposed for changes in structure parameters of the microcapsules on heating.     

钒酸铋黄色颜料的制备——推荐一个无机化学教学实验

该实验以Bi(NO_3)_3和NH_4VO_3为原料,采用液相沉淀法,制备钒酸铋黄色颜料。学生通过控制反应物初始浓度、溶液pH、温度与时间等条件制备分散性良好、颗粒细小、组成均匀的钒酸铋。实验涉及溶液配制、加热搅拌、简易回流、控温、调pH、检验、抽滤、洗涤、干燥等操作。钒酸铋是一种绿色环保的黄色颜料,且具有降解污染物的光催化性能,因此,该实验不仅对于提高学生无机制备实验能力具有很好的教学效果,还在实验教学中渗透了环保理念。     

Rapid Preparation of Mesoporous Methylsilsesquioxane Aerogels by Microwave Heating Technology

Microwave heating technology is known as an alternative to traditional gas and electric heating sources. In this work, mesoporous methylsilsesquioxane (MSQ) aerogels were prepared via a sol–gel process accompanied by microwave heating technology, and microwave heating was used in the gelation of sol and the drying of wet gels, respectively. The effects of hexadecyltrimethylammonium chloride (CTAC) as a surfactant and template, hydrochloric acid (HCl) as a catalyst, ethanol as a solvent, sodium hydroxide (NaOH) as a gelation agent, and microwave power on the pore structure of as-prepared MSQ aerogels were investigated in detail. Microwave heating at low power results in the acceleration of sol–gel transition and achieves the gelation within a few minutes. Appropriate amounts of chemical reagents and microwave heating at high power allow the preparation of mesoporous MSQ aerogels with a BET-specific surface area of 681.6 m²·g⁻¹ and a mesopore size of 19 nm, and the resultant MSQ aerogel still has a BET specific surface area as high as 134 m²·g⁻¹ after heat treatment at 600 °C for 2 h, showing high thermal stability. The MSQ aerogels/fibre composite possesses a low thermal conductivity of 0.039 W/(m·k)⁻¹, displaying good thermal insulation. Microwave heating technology is a promising heating method for the preparation of other aerogels.     

Microwave Heating Outperforms Conventional Heating for a Thermal Reaction that Produces a Thermally Labile Product: Observations Consistent with Selective Microwave Heating

Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high‐temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron‐demand dehydro‐Diels–Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations.     

Polyhedral oligomeric silsesquioxanes (POSS) thermal degradation

The mechanism of thermal degradation of several substituted polyhedral oligomeric silsesquioxanes (POSS) cages is studied in this work.Hydrogen POSS and methyl POSS shows incomplete sublimation on heating, both in inert atmosphere and in air. Isobutyl and octyl substituted POSS undergo an almost complete evaporation when heated in inert atmosphere. In air, oxidation competes with volatilization, producing a considerable amount of silica-like residue on heating up to 800 °C.Phenyl POSS shows a higher thermal stability than saturated aliphatic POSS and limited volatility, producing a ceramic residue at high yield on heating in nitrogen, composed of a silica containing a considerable amount of free-carbon. A lower amount of residue is shown after heating in air, corresponding to the POSS Si-O fraction.A vinyl POSS cage/network resin is also studied, in comparison to above materials, showing the highest ceramic yield.     

电化聚合聚吡咯的角分布X射线光电子能谱研究

用角分布Ｘ射线光电子能谱（ＸＰＳ）测试和样品原位加热相结合的方法研究了阴离子是对甲苯磺酸根的电生导电聚吡咯的化学和聚集态结构．其结果表明聚吡咯表面约几个原子层内原子的相对浓度依下述次序递减：Ｃ＞Ｏ＞Ｓ＞Ｎ；导电聚吡咯中的氮原子至少有吡咯氮和氧化态氮两种；在２００℃加热以后聚合物链不受影响，但阴离子向表面迁移，同时氧化态氮大大减少．     

Polymer crystallization and reorganization during heating: Simulation with the sadler/gilmer model

Polymer crystallization and melting under nonisothermal conditions are investigated by means of an extended version of the two-dimensional Sadler / Gilmer pinning model. In particular, the case of a constant heating rate is simulated. Lamellar thickening and eventual melting are studied for a range of heating rates and initial temperatures. An approach to equilibrium (i.e. infinite thickness at T^o_m) by slowing down the heating rate is found to be more than exponentially suppressed. Similarities with heating experiments on polyethylene and PEEK are demonstrated. © 1993 John Wiley & Sons, Inc.     

Study on nonlinear phase‐separation for PMMA/α‐MSAN blends by dynamic rheological and small angle light scattering measurements

The phase‐separation behavior of poly(methyl methacrylate)/poly(α‐methyl styrene‐co‐acrylonitrile) (PMMA/α‐MSAN) blends upon heating was studied through dynamic rheological measurements and time‐resolved small angle light scattering, as a function of temperatures and heating rates. The spinodal temperatures could be obtained by an examination of the anomalous critical viscoelastic properties in the vicinity of phase‐separation induced by the enhanced concentration fluctuation on the basis of the mean field theory. It is found that the dependence of the critical temperatures determined by dynamic rheological measurements and small angle light scattering on heating rates both deviates obviously from the linearity, even at the very low heating rates. Furthermore, the cloud‐point curves decrease gradually with the decrease of heating rates and present the trend of approaching T_gs of the blends. The nonlinear dependence is in consistence with that extracted from the isothermal phase‐separation behavior as reported in our previous paper. It is suggested that the equilibrium phase‐separation temperature could be hardly established by the linear extrapolating to zero in the plotting of cloud points versus heating rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1547–1555, 2006     

A method for constant-rate heating of milligram-sized samples

Heating a milligram-sized sample of material at a constant heating rate is usually achieved by controlling the temperature of an electric-resistance furnace with a proportional integral derivative (PID) controller. Here we present a new method for constant-rate heating that is based on a semi-empirical mathematical expression relating sample temperature, heating rate, and electric power supplied to the furnace. This method uses PID control only for second-order corrections of the heating rate. The linearity of the sample temperature vs. time curves obtained by applying this method to a simple furnace setup is the same as the linearity of the curves generated by modern commercial thermogravimetric analyzers.     

Heating and temperature gradients of lipid bilayer samples induced by RF irradiation in MAS solid‐state NMR experiments

The MAS solid‐state NMR has been a powerful technique for studying membrane proteins within the native‐like lipid bilayer environment. In general, RF irradiation in MAS NMR experiments can heat and potentially destroy expensive membrane protein samples. However, under practical MAS NMR experimental conditions, detailed characterization of RF heating effect of lipid bilayer samples is still lacking. Herein, using ¹H chemical shift of water for temperature calibration, we systematically study the dependence of RF heating on hydration levels and salt concentrations of three lipids in MAS NMR experiments. Under practical ¹H decoupling conditions used in biological MAS NMR experiments, three lipids show different dependence of RF heating on hydration levels as well as salt concentrations, which are closely associated with the properties of lipids. The maximum temperature elevation of about 10 °C is similar for the three lipids containing 200% hydration, which is much lower than that in static solid‐state NMR experiments. The RF heating due to salt is observed to be less than that due to hydration, with a maximum temperature elevation of less than 4 °C in the hydrated samples containing 120 mmol l^?1 of salt. Upon RF irradiation, the temperature gradient across the sample is observed to be greatly increased up to 20 °C, as demonstrated by the remarkable broadening of ¹H signal of water. Based on detailed characterization of RF heating effect, we demonstrate that RF heating and temperature gradient can be significantly reduced by decreasing the hydration levels of lipid bilayer samples from 200% to 30%. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal decomposition of Ni(II) and Fe(III) acetates and their mixture

The thermal decomposition of the ferric and nickel acetate salts has been followed. It was found that the heating rate affects the decomposition steps. For a heating rate of 1 K min^–1 the product is either Fe₂O₃ or NiO. For a higher heating rate the suboxides are obtained and reoxidized again on further heating. The decomposition of the mixed salt is an overlap of the DTA for the separate salts but the decomposition reactions are shifted to lower temperatures.We would like to thank Prof. Dr. N. Afify, Phys. Dept., Fact. Science, Assiut University, for experimental assistance and valuable discussions.     

Theoretical Simulations of Thermochromic and Aggregation-Induced Emission Behaviors of a Series of Red-Light Anthracene-o-carborane Derivatives

Quantum mechanical and molecular dynamics simulations have been carried out on a series of anthracene-o-carborane derivatives (ANT-H, ANT-Ph, ANT-Me and ANT-TMS) with rare red-light emission in the solid state. The simulation of the heating process of the crystals and further comparison of the molecular structures and excited-state properties before and after heating help us to disclose the thermochromic behavior, that is, the red-shift emission is caused by elongation of the C1−C2 bond in the carborane moiety after heating. Thus, we believe that the molecular structure in the crystal is severely affected by heating. Transformation of the molecular conformation appears in the ANT-H crystal with increasing temperature. More specifically, the anthracene moiety moves from nearly parallel to the C1−C2 bond to nearly perpendicular, causing the short-wavelength emission to disappear after heating. As for the aggregation-induced emission phenomenon, the structures and photophysical properties were investigated comparatively in both the isolated and crystal states; the results suggested that the energy dissipation in crystal surroundings was greatly reduced through hindering structure relaxation from the excited to the ground state. We expect that discussion of the thermochromic behavior will provide a new analysis perspective for the molecular design of o-carborane derivatives.     

Studies on preparation of HDPE/CB composites including a novel oriented structure by the microwave heating and their characterization

Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high‐density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X‐ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin‐core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.