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The dielectric behavior and microwave absorption (MA) performance of doped semiconductor indium tin oxide (ITO)/nanoporous carbon (NPC) composites were scanned by a combination of simulations and experiments. In this work, designed homogeneous ITO/NPC composites were synthesized for the first time by the direct pyrolysis of In metal-organic framework doped with Sn (In/Sn-MOFs). Precise regulation of the complex permittivity of ITO/NPC was possible by controlling the carrier concentration, which resulted in superior MA performance. In addition, the conductive network of NPC, large surface areas & pore volumes and abundant heterogeneous interface of ITO/NPC were found to be the key aspects for MA performance. When the ratio of Sn/In was 1:9, ITO/NPC-2 exhibited outstanding MA property at low frequency. At 4.57 GHz and 4.10 mm, the maximum RL value of −60.55 dB was reached; while the RL values below −8 dB were found in the low-frequency range of 3.72–5.42 GHz. In addition, a strong reflection loss (RL) of −45.12 dB was obtained at 12.90 GHz and a small thickness of 1.55 mm. This work might provide a convenient and novel method for the construction of low frequency microwave absorbers.

Multi-composite materials with heterostructure derived from metal-organic frameworks (MOFs) have been extensively used in electromagnetic wave (EMW) absorbing applications because of their peculiar microstructure and electromagnetic characteristics. A series of Co, metal oxide semiconductor (MOS), and nanoporous carbon (NPC) composites with multi-nut-bread structure were developed by the one-step pyrolysis of capsule MOFs@MOFs, in which a surfactant assisted the fabrication of bi-MOFs constructed through different metal ions and organic ligands by an electrostatic effect. The impedance matching and attenuation ability of the absorbers were adjusted by tuning the type and content of “nuts” with different electromagnetic characteristics. The results showed that all the composites exhibited outstanding microwave absorbing (MA) performance. Specifically, the Co/ZnO/NPC-2 composite achieved the maximum reflection loss value (RLmax) of −61.7 dB and the optimal effective bandwidth (fe, RL ≤ −10 dB) of 5.6 GHz with a 1.88 mm thickness. The Co/ITO/NPC-2 (ITO = indium tin oxide) composite presented an RLmax of −55.1 dB at an ultra-thin thickness of 1.32 mm. In addition, an ultra-broad fe of 6.4 GHz was measured for the composite Co/TiO2/NPC-2 with a thickness of 2.05 mm. The excellent MA performance of the composites was related to their unique multi-nut-bread structure, and the synergistic effect between the magnetic and dielectric behavior. This work provides a reliable strategy for synthesizing microcapsule MOFs@MOFs with different metal ions and organic ligands, and provides a new insight for constructing multi-interfacial ternary composites with advanced MA properties.

Nano-porous carbon (NPC) composites derived from metal-organic frameworks (MOFs) possess effective microwave absorption (MA) properties. However, the fabrication of MOF-derived NPC composites with full-band MA performance is challenging. In this work, the effect of the bandgap on the microwave dielectric behavior of Mn-MOF derivatives was investigated. The results demonstrated that a narrower MnO2 bandgap resulted in higher conductivity and a larger dielectric constant of the corresponding materials. The three-dimensional (3D) MnO@NPC composites achieved excellent low-frequency MA ability. The maximum reflection loss (RL) of MnO@NPC carbonized at 800 °C reached −54.38 dB at 5.12 GHz. The 1D-3D mixed-dimensional MnO2@NPC composites with the ultra-strong MA response in the full band were obtained by oxidizing MnO@NPC to MnO2@NPC. MnO2@NPC-800 showed superior MA capacity with the maximum RL value equal to −63.21 dB at 12.48 GHz and 2.05 mm thickness. The maximum RL values in S, C, X, Ku bands also exceeded −50 dB. Such an outstanding MA performance of MnO2@NPC-800 composite was attributed to the MnO2 presence and its multi-dimensional structure. This work provides the foundation for the fabrication of MOF-derived materials capable of full-band MA.

A key aspect of refining the design and manufacture of contemporary microwave absorbing materials is to improve their absorption of electromagnetic radiation at low frequency which has proved to be an immensely challenging task. This work reports a relatively uncomplicated method to design core-shell absorbers through nanoporous carbon (NPC) obtained by removing redundant Cu from the pyrolysis products of HKUST-1 (HKUST is the Hong Kong University of Science and Technology) coated with (1R,2R)-(−)-1,2-cyclohexanediamineferrocene formaldehyde polyschiff base iron (II) (CPI). Three NPC@CPI samples not only maintain good impedance matching of the pyrolysis products of HKUST-1, but also increase the attenuation abilities significantly due to the synergetic effect of multiple interfacial polarization, cross-polarization and Debye relaxation, which further leads to their outstanding microwave absorbing performance. When the mass ratio of CPI to NPC is 6.7:100 (NPC@CPI-1), the strongest reflection loss (RL) can achieve −60.8 dB at 3.7 GHz, whereas the RL bandwidth under −10 dB can become as much as 5.6 GHz at 1.65 mm. While CPI to NPC is 10:100 (NPC@CPI-2), an optimal RL of −46.9 dB at 11.7 GHz and 1.9 mm can be achieved. This work thus provides an excellent model for the design and the manufacture of thin, lightweight, broad, and strong EM absorbers based on MOFs derivatives and chiral polymers.

Blocked mercaptosilane possessing two functionally active end groups can chemically react with both silica and rubber leading to significant improvement in silica-filled vulcanizate products. The effect of the novel blocked mercaptosilane (3-propionylthio-1-propyltrimethoxylsilane) (called hereafter PXT) on the structure, mechanical, and dynamic mechanical properties of NR/silica composite were studied. Equilibrium swelling test and scanning electron microscope (SEM) indicate that PXT is able to enhance the crosslinking density of natural rubber (NR)/silica composites and the dispersion of silica in matrix. Mechanical measurement of properties show that PXT can strengthen the reinforcement of silica for NR vulcanizate. In the presence of PXT, the resistance to flex cracking, abrasion and dynamic compression fatigue, and heat build-up of NR/silica composites can be improved substantially. For the application of automotive tire, it also obtains high-skid resistance and low-rolling resistance simultaneously at 2 phr of the PXT concentration. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

A novel block mercaptosilane (3-benzothiazolthio-1-propyltriethoxylsilane) (Silane-M) was synthesized and characterized by Fourier transform infrared spectra, 1H nuclear magnetic resonance, and elemental analysis. Styrene–butadiene rubber (SBR)/silica composites were prepared with Silane-M, and its effect on the properties of materials was studied. Results show that Silane-M can substantially improve the dispersion of silica and strengthen the reinforcement of silica for SBR vulcanizates like anchors of silica to rubber matrix. As expected, it enhances the tensile, tear strength, dynamic compression property, and resistance to abrasion of SBR/silica composites. By adding Silane-M into the system, SBR/silica composites get superior skid resistance and high glass transition temperature (Tg). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The isothermal crystallization behavior of neat polypropylene (PP) and solid-phase graft copolymers of PP with maleic anhydride and methyl methacrylate (PPMM) were compared by differential scanning calorimetry. The Avrami equation and Hoffman theory were applied to describe the isothermal crystallization kinetics. The results show that the fitted isothermal crystallization parameters are similar to the experimental data, and suggest that the Avrami equation is suitable to describe the isothermal crystallization process of PP and PPMM. The grafted side chains on PP can change the nucleation and growth of crystallization. They caused a decrease in the apparent crystallization activation energy and lateral surface free energy, and an increase in the nucleation rate. This was attributed to the grafted side chains not only acting as nucleating agent but also hindering the motion of the molecular chains and reducing the growing rate of crystallization.

In present work, the effect of novel blocked mercaptosilane(3- propionylthio-1-propyltrimethoxylsilane) (called hereafter PXT) on structure and dynamic mechanical properties of natural rubber/silica (NR/silica) composites was studied in efficient, semi-efficient and conventional vulcanization systems. Equilibrium swelling method investigation indicates that PXT is able to enhance crosslinking density of composites. The investigation of properties shows that PXT can strengthen the reinforcement of silica for NR vulcanizates and substantially enhance the resistance to flex cracking and abrasion of NR/silica composites. Since PXT possess two functionally active end groups which can chemically react with both silica and rubber, at 2 phr of the PXT content, NR/silica composites possess optimum comprehensive dynamic mechanical properties.