Lead halide perovskite nanowires stabilized by block copolymers for Langmuir-Blodgett assembly

The rapid development of solar cells based on lead halide perovskites (LHPs) has prompted very active research activities in other closely-related fields. Colloidal nanostructures of such materials display superior optoelectronic properties. Especially, one-dimensional (1D) LHPs nanowires show anisotropic optical properties when they are highly oriented. However, the ionic nature makes them very sensitive to external environment, limiting their large scale practical applications. Here, we introduce an amphiphilic block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-P4VP), to chemically modify the surface of colloidal CsPbBr₃ nanowires. The resulting core-shell nanowires show enhanced photoluminescent emission and good colloidal stability against water. Taking advantage of the stability enhancement, we further applied a modified Langmuir-Blodgett technique to assemble monolayers of highly aligned nanowires, and studied their anisotropic optical properties.

     

加速天然气开发利用完成化肥生产自给

天煤气是我国发展国民经济的宝贵能源之一,又是生产化肥最经济合理的原料。本文提出用天然气资源,以现有大型蒸汽转化制氨装置在节气、节能、增产等方面进行技术改造,完成化肥生产自给的规划设想,仅供决策部门研究参考。     

Damage and failure mechanisms of a3-directional carbon/carbon composite under uniaxial tensile and shear loads

The mechanical behavior of a three-directional carbon/carbon (C/C) composite under tensile and shear loads is investigated in relation with the failure mechanisms and, the fiber architecture. This three-directional C/C composite was produced by Chemical Vapor Infiltration of a needled fiber preform of multiple layers of satin woven tows. The C/C composite exhibited several interesting features including an essentially non-linear stress–strain behavior and permanent deformations. Three families of matrix cracks were identified under tensile and shear loads, including microcracks in the tows, intertow delamination and cracks across the longitudinal tows. It was found that the delamination cracks affect preponderantly the stress–strain behavior and the mechanical properties. Similar features in the mechanical behavior and the failure mechanisms were highlighted under tension and under shear loading.

Résumé

Le comportement mécanique d’un composite Carbone/Carbone 3D sous chargement de traction et de cisaillement est étudié. Ce matériau composite C/C a étéobtenu par densification par C.V.I. (Chemical Vapor Infiltration) d’une préforme fibreuse aiguilletée normalement au plan du tissu. Les relations entre les courbes de comportement mécanique, les mécanismes de dégradation identifiés par microscopie optique et l’architecture fibreuse de la structure ont étéétablies. Ce matériau composite C/C présente un comportement mécanique non linéaire jusqu’àrupture avec déformations anélastiques. Les trois mêmes familles de fissures matricielles ont étéidentifiées sous chargement de traction et de cisaillement, àsavoir la fissuration intra-fil, la fissuration inter-fils, et, la fissuration intra et inter-fils. La fissuration inter-fil, et, la fissuration intra et inter-fils affectent majoritairement le comportement mécanique. Les similitudes importantes observées entre le comportement mécanique et les mécanismes de rupture sous sollicitations de traction et de cisaillement sont discutées.