A family of red light-emitting star-shaped porphyrins with four monodisperse conjugated oligofluorene arms was prepared by using two key reactions: Lindsey condensation and Suzuki-Miyaura cross coupling reactions. All porphyrins exhibit high quantum yields (about 0.22) and good solubility in common organic solvents, and form high-quality solid films. Optical studies showed that the star-shaped oligomers could absorb blue light and emit saturated red light via efficient energy transfer from the fluorene segments to the porphyrin core.
Abstract:Carbon nanotubes (CNT) have remarkable mechanical properties with very high elastic modulus and electrical conductivity. Shape memory polymer (SMP) as one of smart materials is characterized with its remarkable recoverability and shape memory effect, but its mechanical properties such as strength and elastic modulus is not high enough. In this study, CNT/SMP nanocomposites were developed with the typical CNTs of the vapor growth carbon fibers (VGCFs). A fine and homogeneous dispersion of VGCF throughout the SMP matrix is obtained. The specimens with different VGCF weight fraction, such as SMP bulk, 1.7wt%, 3.3wt% and 5.0wt%, were prepared, and their dynamic mechanical properties and shape recovery behavior were investigated. It was found that storage elastic modulus is improved obviously with increment of VGCF weight fraction, and the CNT/SMP nanocomposites showed a good shape memory effect. It is indicated that the recovery stress of CNT/SMP nanocomposites with only 3.3% weight fraction of carbon nanotubes will reach almost twice of that in SMP bulk.
Uniform BaTiO(3) nanotubes were synthesized via a simple wet chemical route at low temperature (50 °C). The as-synthesized BaTiO(3) nanotubes were characterized using powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that the BaTiO(3) nanotubes formed a cubic phase with an average diameter of ~10 nm and wall thickness of 3 nm at room temperature. The composition of the mixed solvent (ethanol and deionized water) was a key factor in the formation of these nanotubes; we discuss possible synthetic mechanisms. The microwave absorption properties of the BaTiO(3) nanotubes were studied at microwave frequencies between 0.5 and 15 GHz. The minimum reflection loss of the BaTiO(3) nanotubes/paraffin wax composite (BaTiO(3) nanotubes weight fraction = 70%) reached 21.8 dB (~99.99% absorption) at 15 GHz, and the frequency bandwidth less than -10 dB is from 13.3 to 15 GHz. The excellent absorption property of BaTiO(3) nanotubes at high frequency indicates that these nanotubes could be promising microwave-absorbing materials.
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