Thermal-Robust Phenoxyimine Titanium Catalysts Bearing Bulky Sidearms for High Temperature Ethylene Homo-/Co- Polymerizations

A family of titanium complexes (Ti1-Ti7) with the general formula LTiCl3, supported by tridentate phenoxyimine [O-NO] ligands (L1-L7) bearing bulky sidearms, were synthesized by treating the corresponding ligands with stoichiometric amount of TiCl4. All the ligands and complexes were well characterized by 1H and 13C NMR spectroscopies, in which ortho- methoxyl groups on N-aryl moieties shifted to downfield, corroborating the successful coordination reaction. Structural optimization by DFT calculations revealed that one of the phenyl groups on dibenzhydryl moiety could form π-π stacking interaction with the salicylaldimine plane, because of which the obtained titanium complexes revealed good thermal stabilities for high-temperature polymerization of ethylene. The thermal robustness of the complexes was closely related to the strength of π-π stacking interactions, which were mainly influenced by the substituents on the dibenzhydryl moieties; Ti1, Ti4 and Ti5 emerged as the three best-performing complexes at 110 °C. With the aid of such π-π stacking interactions, the complexes were also found to be active at >150 °C, although decreased activities were witnessed. Besides homopolymerizations, complexes Ti1-Ti7 were also found to be active for the high-temperature copolymerization of ethylene and 1-octene, but with medium incorporation percentage, demonstrating their medium copolymerization capabilities.

Temperature effects on the jumping performance of house crickets

Insect jumping and other explosive animal movements often make use of elastic-recoil mechanisms to enhance performance. These mechanisms circumvent the intrinsic rate limitations on muscle shortening, allowing for greater power production as well as thermal robustness of the associated movements. Here we examine the performance and temperature effects on jumping in the house cricket, Acheta domesticus, using high-speed imaging and inverse dynamics analysis. We find that adult house crickets jumped with greater performance than would be possible using direct muscle shortening, generating a peak power of over 2000 W/kg of muscle mass and maintaining high performance across the entire tested range of body temperatures (12-32°C). Performance declined at the lowest temperature (12°C), yet jump power still exceeds available muscle power. These results reveal that Acheta domesticus makes use of an elastic-recoil mechanism that enhances both the performance and thermal robustness of jumping.

Thermal sensitivity of Axolotl feeding behaviors

Musculoskeletal movement results from muscle contractions, recoil of elastic tendons, aponeuroses, and ligaments, or combinations thereof. Muscular and elastic contributions can vary both across behaviors and with changes in temperature. Skeletal muscles reach peak contraction speed at a temperature optimum with performance declining away from that optimum by approximately 50% per 10 °C, following the Q10 principle. Elastic recoil action, however, is less temperature sensitive. We subjected Axolotls (Ambystoma mexicanum) to changes from warm (23 °C), via medium (14 °C), to cold (6 °C) temperature across most of their thermal tolerance range, and recorded jaw kinematics during feeding on crickets. We sought to determine if suction feeding strikes and food processing chews involve elastic mechanisms and, specifically, if muscular versus elastic contribution vary with temperature for gape opening and closing. Measurements of peak and mean speed for gape opening and closing during strikes and chews across temperature treatments were compared to Q10-based predictions. We found that strike gape speed decreased significantly from warm and medium to cold treatments, indicating low thermal robustness, and no performance-enhancement due to elastic recoil. For chews, peak and mean gape closing speeds, as well as peak gape opening speed, also decreased significantly from warm to cold treatments. However, peak gape opening and closing speeds for chews showed performance-enhancement, consistent with a previously demonstrated presence of elastic action in the Axolotl jaw system. Our results add to a relatively small body of evidence suggesting that elastic recoil plays significant roles in aquatic vertebrate feeding systems, and in cyclic food processing mechanisms.

Highly Enhanced Thermal Robustness and Photothermal Conversion Efficiency of Solar-Selective Absorbers Enabled by High-Entropy Alloy Nitride MoTaTiCrN Nanofilms

Recent advances in high-entropy alloys have spurred many breakthroughs in the fields of high-temperature materials and optical materials and they provide incredible application potentialities for photothermal conversion systems. Solar-selective absorbers (SSAs), as key components, play a vital role in photothermal conversion efficiency and service life. The most pressing problem with SSAs is their inconsistent optical performance, an instability constraint induced by thermal stress. A feasible method of improving performance stability is the introduction of high-entropy materials, such as high-entropy alloy nitrides. In this study, enabled by an intrinsic MoTaTiCrN absorption layer, the solar configuration achieves greatly enhanced, exceptional thermotolerance and optical properties, leading to the formation of a scalable, highly efficient, and cost-effective structure. Computational and experimental approaches are employed to achieve optimum preparation parameters for thicknesses and constituents. The crystal structure of high-entropy ceramic MoTaTiCrN is fully investigated, including thickness-dependent crystal nucleation. High-temperature and long-term thermal stability tests demonstrate that our proposed SSA is mechanically robust and chemically stable. Moreover, a low thermal emittance (15.86%) at 500 °C promotes the photothermal conversion efficiency. In addition, due to the exceptional spectral selectivity (α/ε = 92.3/6.5%), thermal robustness (550 °C for 168 h), and photothermal conversion efficiency (86.9% at 550 °C under 100 sun), it is possible for our proposed SSA to enhance the practical realization of large-area photothermal conversion applications, especially for concentrated solar power systems.