Dynamic behavior of short aramid fiber‐filled elastomer composites

Short fiber reinforcement is a suitable way to improve the tribological properties of elastomers. However, rubbers products are often exposed to highly dynamic mechanical loadings. Hereby it is crucial to study the change in dynamic behavior due to the addition of short fibers. Therefore, these properties were investigated in terms of dynamic mechanical thermal analysis, heat build‐up (HBU), and fatigue crack growth resistance under cyclic loadings for two different rubber compounds. A peroxide cured ethylene–propylene–diene rubber (EPDM) and a sulfur cured natural rubber (NR) compound were chosen and reinforced with two types of short aramid fibers. It was found that the short fibers could contribute to the improvement in the crack growth resistance, HBU, and the dynamic mechanical behavior of the composites depending on the testing conditions. POLYM. ENG. SCI., 54:2958–2964, 2014. © 2014 Society of Plastics Engineers     

Dichlorocarbene‐Functionalized Fluorographene: Synthesis and Reaction Mechanism

Halogen functionalization of graphene is an important branch of graphene research as it provides opportunities to tailor the band gap and catalytic properties of graphene. Monovalent C–X bond obviates pitfalls of functionalization with atoms of groups 13, 15, and 16, which can introduce various poorly defined groups. Here, the preparation of functionalized graphene containing both fluorine and chlorine atoms is shown. The starting material, fluorographite, undergoes a reaction with dichlorocarbene to provide dichlorocarbene‐functionalized fluorographene (DCC‐FG). The material is characterized by X‐ray photoelectron spectroscopy, Raman spectroscopy, and high‐resolution transmission electron microscopy with X‐ray dispersive spectroscopy. It is found that the chlorine atoms in DCC‐FG are distributed homogeneously over the entire area of the fluorographene sheet. Further density functional theory calculations show that the mechanism of dichlorocarbene attack on fluorographene sheet is a two‐step process. Dichlorocarbene detaches fluorine atoms from fluorographene sheet and subsequently adds to the newly formed sp² carbons. Halogenated graphene consisting of two (or eventually three) types of halogen atoms is envisioned to find its way as new graphene materials with tailored properties.     

Magnetic Polaron States in Photoluminescent Carbon Dots Enable Hydrogen Peroxide Photoproduction (Small 32/2023)

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induces the generation of spin-separated species, including electron/hole (e⁻/h⁺) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e⁻/h⁺ pairs and triplet species depends on the solvent polarity, featuring a substantial stabilization of the triplet state in a non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerge from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties are dissected theoretically by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakelike model systems, revealing the importance of size dependence and interlayer effects. The formation of the spin-separated states in Asp-CDs enables the photoproduction of hydrogen peroxide (H₂O₂) from water and water/2-propanol mixture via a water oxidation reaction.     

Antenna Protein Clustering In Vitro Unveiled by Fluorescence Correlation Spectroscopy

Antenna protein aggregation is one of the principal mechanisms considered effective in protecting phototrophs against high light damage. Commonly, it is induced, in vitro, by decreasing detergent concentration and pH of a solution of purified antennas; the resulting reduction in fluorescence emission is considered to be representative of non-photochemical quenching in vivo. However, little is known about the actual size and organization of antenna particles formed by this means, and hence the physiological relevance of this experimental approach is questionable. Here, a quasi-single molecule method, fluorescence correlation spectroscopy (FCS), was applied during in vitro quenching of LHCII trimers from higher plants for a parallel estimation of particle size, fluorescence, and antenna cluster homogeneity in a single measurement. FCS revealed that, below detergent critical micelle concentration, low pH promoted the formation of large protein oligomers of sizes up to micrometers, and therefore is apparently incompatible with thylakoid membranes. In contrast, LHCII clusters formed at high pH were smaller and homogenous, and yet still capable of efficient quenching. The results altogether set the physiological validity limits of in vitro quenching experiments. Our data also support the idea that the small, moderately quenching LHCII oligomers found at high pH could be relevant with respect to non-photochemical quenching in vivo.     

Beyond binary correctness: Classification of students’ answers in learning systems

User Modeling and User-Adapted Interaction - Adaptive learning systems collect data on student performance and use them to personalize system behavior. Most current personalization techniques focus...     

Co‐processing of Waste Cooking Oil and Light Cycle Oil with NiW/(Pseudoboehmite + SBA‐15) Catalyst

Light cycle oil (LCO) and waste sunflower cooking oil (WSO) were co‐processed with the aim of obtaining more environmentally friendly fuels. Partial hydrogenation of naphthalene was also investigated as a model reaction. Commercial NiW/SiO₂‐Al₂O₃, as a reference catalyst, and NiW/(pseudoboehmite + SBA‐15), as a new research catalyst, were tested. Liquid products were analyzed by simulated distillation, elemental analysis, and FTIR spectroscopy. Elemental analysis indicated higher efficiency of the research catalyst in hydrodesulfurization, hydrodenitrogenation, and hydrodeoxygenation of pure LCO and mixed feedstock containing WSO. Reactions with pure WSO resulted in less sulfur leaching into the product and a lower degree of deoxygenation compared with the commercial catalyst.     

Rapid Models for Predicting the Low‐Temperature Behavior of Diesel

The cold filtration plugging point (CFPP) is the method most commonly applied to characterize the low‐temperature behavior of diesel and its components. However, this method is time‐consuming and does not have good repeatability, especially for samples with very low CFPP values like kerosene, light cycle oil, etc. Three new models for CFPP prediction were developed and compared: a combined density and distillation curve, differential scanning calorimetry, and near‐infrared. A set of 133 samples of diesel components were used to create the models, containing streams from different sources and levels of treatment. A further 28 diesel samples were used to validate and compare the models. All three models not only were faster than the standard method but also were found to be in good agreement with CFPP values. Each model has its own particular advantages suiting it to a particular type of diesel sample and stage of the diesel production process.