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Photoluminescence of (Zn, Pb, Mn)S Quantum Dots in Polyacrylate Matrix
摘要： Solutions of (Zn, Pb, Mn)S quantum dots with different molar ratios between cations are produced by colloidal synthesis in a methyl methacrylate (MMA) medium. By the thermal polymerization of MMA in a block, the colloidal solutions are converted into the vitreous state. The optical transparency of the poly(MMA)/(Zn, Pb, Mn)S composites at the wavelengths >500 nm reaches 90% at a thickness of the absorbing layer up to 5 mm. The photoluminescence of the composites in the spectral range 400–480 nm is defined by the recombination of electrons at the levels of defects of the ZnS crystal structure, and photoluminescence in the range 520–620 nm by the 4T1 → 6A1 electronic transition in Mn2+ ions. Photoluminescence excitation is a result of interband transitions in ZnS, with energy transfer from the conduction band of ZnS to the levels of Mn2+ ions. The luminescence spectrum depends on the molar ratio between Mn2+ and Pb2+ ions, the order of introduction of substances into the reaction mixture, and the excitation-radiation wavelength.
关键词： acrylate composites,lead ions,doping,luminescence,manganese ions,zinc sulfide,quantum dots
更新于2025-09-23 15:21:01
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Effect of laser surface melting on surface integrity of Ala??4.5Cu composites reinforced with SiC and MoS2
摘要： Two types of composites were prepared with Al?4.5Cu alloy as a matrix using stir casting method. One was reinforced with 10 wt.% of SiC and 2 wt.% of MoS2. The other was reinforced with 10 wt.% of SiC and 4 wt.% of MoS2. Their surfaces were remelted using a CO2 laser beam with an objective to study the influence of laser surface melting (LSM). The topography, microhardness, corrosion resistance and wear resistance of the laser melted surfaces were studied. Overall surface integrity after LSM was compared with as-cast surface. LSM enhanced the microhardness and wear resistance of the surface in each case. Porosity of the laser melted surface was low and corrosion resistance was high. Thus, LSM can be conveniently applied to enhancing the surface integrity of the aluminium composites. However, there is an optimum laser specific energy, around 38 J/m2 in this study, for obtaining the best surface integrity.
关键词： microhardness,aluminium composites,laser surface melting,corrosion resistance,molybdenum disulfide,silicon carbide
更新于2025-09-23 15:21:01
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Nanoparticle Gradient Materials by Centrifugation
摘要： Nanoparticle gradient materials are a unique class of functional materials. They combine the specific properties of nanoparticles with macroscopic materials. A continuous spatial gradient of the nanoparticle concentration leads to diverse physical property profiles. Therefore, these materials have a remarkable potential for applications in optics, electronics, and sensors. A novel approach for the defined and controlled synthesis of this material class is the fabrication in ultracentrifugal fields. The formation of a nanoparticle gradient by sedimentation in a gelatin solution is monitored online with optical systems inside an analytical ultracentrifuge. As soon as the desired nanoparticle concentration gradient is generated, the material is solidified by gelation and the desired gradient is fixed in the material. Application of the established theory of analytical ultracentrifugation allows simulations of the sedimentation process of the nanoparticles in advance. Thus, desired nanoparticle gradient materials can also be tailor-made and fabricated on a preparative scale. This is demonstrated for the example of spherical gold nanoparticles of different sizes, gold nanorods, mixtures thereof, and spherical superparamagnetic iron oxide nanoparticles.
关键词： composites,gradient materials,analytical ultracentrifugation,nanoparticles,polymers
更新于2025-09-23 15:21:01
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Intimate contact development during laser assisted fiber placement: Microstructure and effect of process parameters
摘要： Intimate contact development under LAFP-specific thermal and mechanical boundary conditions/interactions and the effect of process parameters are investigated. One-layer, unidirectional strips of CF/PEKK material were placed with different process parameters on a flat tool surface to create different intimate contact conditions. The concept of effective intimate contact, which is based on the resin content at the surface, is introduced and a methodology to measure it from surface micrographs is provided. Degree of effective intimate contact measured from the samples was compared with the existing intimate contact models. The temperature history in the compaction zone was estimated with a finite element model and pressure sensitive films were used to determine the compaction pressure. It is shown that in addition to the squeeze flow mechanism, which is the base for the current intimate contact models, through-thickness percolation flow of the resin needs to be considered to explain the effective intimate contact development.
关键词： B. Microstructures,C. Process modeling,E. Automated fiber placement (AFP),A. Polymer-matrix composites (PMCs)
更新于2025-09-23 15:21:01
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Inorganic and Composite Fibers || Photocatalytic Properties of TiO2 Composite Nanofibers Electrospun With Different Polymers
摘要： Electrospinning offers the possibility to create fibers with very fine diameters. Spinning ultrafine fibers with diameters in the range of some hundred nanometers from melt or solution has been established some decades ago. With electrospinning, depending on the exact technology, either continuous fibers or fiber mats with relatively narrow diameter distributions can be created from a broad range of materials, starting from polymers to composites and even ceramics. Due to their large inner surface area, nanofiber mats are typically used as filter materials, catalyzers, medical wound dressing, or for promotion of cell growth in biomedical applications. Electrospinning ceramic nanofibers can be performed by co-spinning a blend of polymer and ceramic precursor, followed by calcination to remove the polymer matrix and keep only the ceramic fibers. Alternatively, ceramic nanoparticles can be bonded on the surfaces of polymer nanofibers, or hybrid nanofibers can be formed, consisting of ceramic and polymer materials. In this way, electrospinning can be used to produce a broad variety of nanofibers, besides other typical methods such as self-assembly, use of templates, or drawing, for applications in life sciences, energy storage, dye-sensitized solar cells (DSSCs), electronic and magnetic devices, bonding, etc.
关键词： TiO2 nanofibers,Electrospinning,photocatalytic properties,calcination,polymer composites
更新于2025-09-23 15:21:01
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The rapid and largea??scale production of carbon quantum dots and their integration with polymers
摘要： Carbon quantum dots (CDs) have inspired vast interests due to their prominent photoluminescence (PL) performances and promising applications in optoelectronic, biomedical and sensing fields. Notably, the development of effective approaches for large-scale CDs production may greatly promote the further advancement of their practical applications. In this review, the newly emerging methods for the large-scale production of CDs are summarized, such as microwave, ultrasonic, plasma, magnetic hyperthermia and microfluidic technology. Then, we introduce the available strategies for constructing CDs/polymer composites with intriguing solid-state PL. Particularly, the multiple roles of CDs are emphatically presented, including fillers, monomers and initiators. Moreover, the typical applications of CDs/polymer composites in light-emitting diodes, fluorescent printing and biomedicine are outlined. Finally, we discuss their current problems and speculate on their future development.
关键词： fluorescent materials,carbon dots,carbon dots/polymer composites,large-scale production
更新于2025-09-23 15:21:01
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Grain refinement in laser manufactured Al-based composites with TiB2 ceramic
摘要： Al-based composites reinforced with TiB2 ceramics (1 wt.%, 2 wt.% and 5 wt.%) have been manufactured through selective laser melting (SLM). The results show that the densification, microstructure and mechanical properties of the SLM-processed composites are sensitive to the ceramic particle fraction. The average grain size of the composites decreased from ～6.32 μm with increasing TiB2 fraction from 1 to 5 wt.% respectively. Fine equiaxed grains with narrow size distribution were obtained for composites with relatively high amount of TiB2 particles. The effects of TiB2 ceramic fraction on grain refinement and strengthening mechanisms of SLM-processed composites were discussed. Al-based composite with 2 wt.% TiB2 ceramic was determined to be optimum, especially in the view of manufacturing quality, grain refinement and mechanical properties. The composites at an optimum fraction of 2 wt.% TiB2 exhibited high microhardness of ～127 HV0.2, tensile strength of ～444 MPa, yield strength of ～283 MPa and elongation of ～4.2% owing to collective effects of dispersion and grain refinement strengthening as well as high degree of densification. This study can readily offer reference values for laser additive manufacturing of other metal matrix composites to obtain a good compromise of strength and ductility by tuning reinforcement fraction.
关键词： Selective laser melting (SLM),Mechanical property,Al-based composites,Grain refinement,TiB2 ceramic
更新于2025-09-23 15:21:01
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Mathematical modeling of heat distribution on carbon fiber Poly(ether-ether-ketone) (PEEK) composite during laser ablation
摘要： Since large amounts of energy are transferred precisely to the material in a very short time, laser and material parameters strongly affect the laser process quality. Mathematical modeling of heat distribution during cavity formation on carbon fiber reinforced PEEK composite material was performed. The temperature distribution equation has been obtained by the Fourier method. At the first stage, 1 J energy laser beam was sent onto the material and the cavity on the composite material was obtained. The constants in the temperature distribution equation obtained by making measurements over the cavity were found. Then the cavities were created with 2, 3 and 4 J laser beams to prove its reliability of the model. The results obtained from the measurement on the cavities and calculated from the temperature distribution equation were compared. Since the unidirectional carbon fibers were used, the obtained cavities have an elliptical shape. Verification experiments were carried out using two different heat conduction constants for in direction along fibers and perpendicular to carbon fibers. Experimental results and the mathematical model are in good agreement.
关键词： Mathematical modeling,Fourier method,Laser ablation,Fiber reinforced composites,Poly(ether-ether-ketone) (PEEK)
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Budapest (2018.7.1-2018.7.5)] 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Electrostrictive polymer composites based on liquid crystalline graphene for mechanical energy harvesting
摘要： High electromechanical coupling is critical to perform effective conversion between mechanical and electrical energy for various applications of electrostrictive polymers. Herein, a giant electrostriction effect is reported in liquid crystalline graphene doped dielectric elastomers. The materials are formulated by an original phase transfer method which allows the solubilization of graphenic monolayers in non-polar solvents. Dielectric spectroscopy is combined with tensile test devices to measure the true electrostriction coefficients with differentiating the Maxwell stress effect. Because of their unique liquid crystal structure, the resultant composites show a giant relative permittivity and ultralarge electrostriction coefficient. This work offers a promising pathway to design novel high performance electrostrictive polymer composites as well as to provide insights into mechanisms of true electrostriction in electrically heterogeneous systems.
关键词： polymer composites,electrostriction,graphene
更新于2025-09-23 15:21:01
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Visible Light Photocatalytic Activity of NaYF4:(Yb,Er)-CuO/TiO2 Composite
摘要： TiO2 photocatalysts are limited to ultraviolet light photo-activation, however, by coupling with NaYF4:(Yb,Er) they can utilize visible light activation, but with low efficiencies. In order to enhance visible light photo-activity, CuO nanoparticles were coupled with NaYF4:(Yb,Er) by mechanical ball-milling and coated with TiO2-sol. The coupling of CuO nanoparticles with NaYF4:(Yb,Er)/TiO2 caused the formation of a NaYF4:(Yb,Er)-CuO/TiO2 composite capable of visible absorption with a remarkably reduced band gap of ~2.5 eV. The NaYF4:(Yb,Er)-CuO/TiO2 composite in H2O2 showed the most efficient methylene blue (MB) degradation efficiency of more than 99.5% after exposure to visible light.
关键词： visible light,NaYF4:(Yb,Er)-CuO/TiO2,composites,photocatalyst
更新于2025-09-23 15:21:01