Ming Liu

Phthalonitrile-Based Carbon Foam with High Specific Mechanical Strength and Superior Electromagnetic Interference Shielding Performance.

Electromagnetic interference (EMI) performance materials are urgently needed to relieve the increasing stress over electromagnetic pollution problems arising from the growing demand for electronic and electrical devices. In this work, a novel ultralight (0.15 g/cm(3)) carbon foam was prepared by direct carbonization of phthalonitrile (PN)-based polymer foam aiming to simultaneously achieve high EMI shielding effectiveness (SE) and deliver effective weight reduction without detrimental reduction of the mechanical properties. The carbon foam prepared by this method had specific compressive strength of ∼6.0 MPa·cm(3)/g. High EMI SE of ∼51.2 dB was achieved, contributed by its intrinsic nitrogen-containing structure (3.3 wt% of nitrogen atoms). The primary EMI shielding mechanism of such carbon foam was determined to be absorption. Moreover, the carbon foams showed excellent specific EMI SE of 341.1 dB·cm(3)/g, which was at least 2 times higher than most of the reported material. The remarkable EMI shielding performance combined with high specific compressive strength indicated that the carbon foam could be considered as a low-density and high-performance EMI shielding material for use in areas where mechanical integrity is desired.

Mussel-inspired polydopamine coated hollow carbon microspheres, a novel versatile filler for fabrication of high performance syntactic foams.

Syntactic foams, which can be synthesized by mechanical mixing of hollow microspheres with a matrix material, are a special class of lightweight composite materials. Developing of high-performance syntactic foams remains challenges. In this work, a facile and environmentally friendly surface modification method employing polydopamine (PDA) as a surface treatment agent for hollow carbon microspheres (HCMs) was used, aiming to extend the application of syntactic foams to seldom touched areas. The PDA coating was used as a strategy for interfacial interaction enhancement and also as a platform for further metal coating meant for electromagnetic interference (EMI) shielding. The stronger interfacial interaction between microspheres and polymer matrix provided effective interfacial stress transfer, as a result of the syntactic foams with high strength to weight ratio. Furthermore, the PDA coating on HCMs served as a versatile platform for the growth of noble metals on the surface of PDA-HCMs. Silver nanoparticles was grown by PDA medium. The silver coated HCMs (Ag-PDA-HCMs) impacted the complex permittivity of the syntactic foams leading to high EMI shielding effectiveness (SE). The specific EMI SE reached up to 46.3 dB·cm(3)/g, demonstrated the Ag-PDA-HCMs/epoxy syntactic foam as a promising candidate for lightweight high-performance EMI shielding material.

Polydopamine decoration on 3D graphene foam and its electromagnetic interference shielding properties

3D graphene foam was recently demonstrated to exhibit excellent electromagnetic interference (EMI) shielding performance. In this work, we prepared 3D graphene foams by incorporating a surface modification process of graphene via self-polymerization of dopamine with a subsequent foaming process. The multiple roles played by polydopamine (PDA), including as nitrogen doping source and as an enhancement tool to achieve higher extent of reduction of the graphene through providing wider pathways and larger accessible surface areas were discussed in detail. Despite the presence of the PDA which acted as barriers among the graphene layers that hindered the electrons movement, the enhanced reduction of graphene sheets and the polarization effects introduced by PDA decoration compensated the negative effect of the barrier on EMI shielding effectiveness (SE). As a result, the PDA decorated 3D graphene foams showed improved EMI shielding effectiveness (SE) compared to PDA-free graphene foam (from 23.1 to 26.5dB). More significantly, the EMI shielding performance of the PDA decorated graphene foam was much superior to all existing carbon-based porous materials when the thickness of the specimen was considered.

Synthesis and Exploration of Ladder-Structured Large Aromatic Dianhydrides as Organic Cathodes for Rechargeable Lithium-Ion Batteries

Compared to anode materials in Li-ion batteries, the research on cathode materials is far behind, and their capacities are much smaller. Thus, in order to address these issues, we believe that organic conjugated materials could be a solution. In this study, we synthesized two non-polymeric dianhydrides with large aromatic structures: NDA-4N (naphthalenetetracarboxylic dianhydride with four nitrogen atoms) and PDA-4N (perylenetetracarboxylic dianhydride with four nitrogen atoms). Their electrochemical properties have been investigated between 2.0 and 3.9 V (vs. Li+ /Li). Benefiting from multi-electron reactions, NDA-4N and PDA-4N could reversibly achieve 79.7 % and 92.3 %, respectively, of their theoretical capacity. Further cycling reveals that the organic compound with a relatively larger aromatic building block could achieve a better stability, as an obvious 36.5 % improvement of the capacity retention was obtained when the backbone was switched from naphthalene to perylene. This study proposes an opportunity to attain promising small-molecule-based cathode materials through tailoring organic structures.

A comparative study on electromagnetic interference shielding behaviors of chemically reduced and thermally reduced graphene aerogels

Electromagnetic interference (EMI) shielding performance of chemically and thermally reduced graphene aerogels (GAs) was systematically studied. The EMI shielding mechanisms were extensively analyzed in terms of the distinct surface characteristics resulted from the different reduction methods for the first time. EMI shielding effectiveness (SE) of chemically and thermally reduced GAs reached 27.6 (GAC) and 40.2dB (GAT) at the thickness of 2.5mm, respectively. It was found that the introduction of nitrogen atoms through chemical reduction induced localized charges on the carbon backbone leading to strong polarization effects of GAC. The relatively incomplete reduction caused a large number of side polar groups which prevented the graphene sheets from π-π stacking. In contrast, the higher extent of reduction of graphene sheets in GAT left a smaller amount of side polar groups and formed more sp2 graphitic lattice, both factors favored π-π stacking between the adjacent graphene sheets, resulting in higher electrical conductivity and enhanced EMI SE. The EMI shielding performance of the GAs prepared outperformed the recent reported porous carbon materials with respect to the absolute SE value at the similar thickness and/or density.

Ultrahigh Self-Sensing Performance of Geopolymer Nanocomposites via Unique Interface Engineering

Monitoring and assessment of the health of a civil structural material are the critical requirements to ensure its safety and durability. In this work, a coating strategy on carbon nanotubes (CNTs) was employed for the dispersion of CNTs in geopolymer matrix. The geopolymer nanocomposites prepared exhibited ultrahigh self-sensing performance based on the unique behaviors of SiO2 coating on CNTs in the geopolymer matrix. The SiO2 layer on CNTs was partially or fully removed during the fabrication process to restore the conductive nature of CNTs, facilitating the dispersion of CNTs and forming well-connected 3D electrical conductive networks. The gauge factor (GF) of geopolymer nanocomposites reached up to 663.3 and 724.6, under compressive and flexural loading, respectively, with the addition of only 0.25 vol % of SiO2-coated CNTs (SiO2-CNTs). The values were at least twice higher than those recently reported self-sensing structural materials containing different types of carbon-based fillers. The underlying mechanisms on the electrical signal change with respect to ionic conduction and electronic conduction were explored and correlated to the self-sensing performance. Additionally, the uniform dispersion of CNTs and good interaction between CNTs and geopolymer matrix contributed to the improvement in flexural and compressive strengths.

Thiophene‐Fused‐Heteroaromatic Diones as Promising NIR Reflectors for Radiative Cooling

Developing appropriate NIR-reflective materials to combat near-infrared (NIR) heat radiation (700-2500 nm) from sunlight, avoiding energy accumulation and reduce energy consumption, is important and highly desirable. In this research, four thiophene-fused-heteroaromatic diones were used as basic reflectors to investigate the relationship between their intrinsic molecular structures and NIR-reflective properties. The reflectance intensity can be readily tuned by adjusting the length of the appended aliphatic side chains, as well as the strength of the electron-donating groups. A methoxy-substituted thiophene-fused-heteroaromatic dione showed the best performance in reflecting NIR, and it was used as a coating for a model glass house. The comparison of the internal temperature difference relative to a control house was measured and the maximum temperature was 12 °C lower than that in the control house.

Boosting the performance of organic cathodes through structure tuning

The decisive factor to realize high-capacity rechargeable batteries is the cathode. Since the experimental capacity of inorganic cathodes is usually less than 200 mA h g−1, searching for new cathode materials to boost the capacity is highly desirable. Here, we design and synthesize two novel organic cathodes, poly(pyrene-4,5,9,10-tetraone) (PPTO) and poly(2,7-ethynylpyrene-4,5,9,10-tetraone) (PEPTO), based on the highly redox-active pyrene-4,5,9,10-tetraone. Due to their four Li+ ion intake characteristics, both cathodes show a large reversible capacity of 234 & 244 mA h g−1 and a high energy density of up to 530 & 507 W h kg−1, respectively. In particular, benefiting from the enhanced conjugation and planarity, PEPTO with the addition of a carbon–carbon triple bond (CC) delivers a significantly improved rate stability at high current densities and an excellent capacity retention of 110 mA h g−1 after 1000 cycles (at 800 mA g−1). Our approach could provide an effective strategy to prepare new organic cathodes for the next generation of high stability and high energy density organic batteries through structure tuning.

Pyrene‐Containing Twistarene: Twelve Benzene Rings Fused in a Row

Success in obtaining higher-order twistarenes with precise structures is very important for fundamentally understanding the relationship between the structures and physical properties/optoelectronic applications. In this research, by using the advantages from a retro-Diels-Alder process (clean reaction) and the cross-conjugated nature of the pyrene unit, a novel dodeca-twistarene was prepared for the first time. Its structure, confirmed by single-crystal XRD analysis, indicates that it possesses a twisted angle (≈30°), and two neighboring molecules in the crystal lattice are perpendicular to each other because of the twisted character and the strong intermolecular CH-π interactions. However, its basic physicochemical properties suggest its instability in air derives from its elevated HOMO energy level, although NICS calculations confirm that the pyrene units contribution poorly to the π conjugation of the overall molecule.

Nanofiller reinforcement versus surface treatment effect on the mechanical properties of syntactic foams

Syntactic foams are one of the special kinds of composite materials which can be prepared in a mechanical way by mixing hollow particles (the filler) with a resin system (the binder). To improve the mechanical properties of syntactic foams, in our work, carbon nanofibers (CNFs) were added to reinforce the syntactic foam. Results showed that although the presence of carbon nanofiber improved the mechanical properties of the syntactic foam, it dramatically increased the density, i.e., destroyed the main advantage of syntactic foams. In addition, the introduction of CNFs could cause difficulty in fabrication and increase the production cost. In order to overcome these problems, two approaches of the surface treatment of hollow microspheres, namely coupling agent and polydopamine (PDA) coating, were applied. Results showed that better interfacial adhesion between hollow microspheres and matrix could be induced from both coupling agent and PDA treated hollow microspheres, which led to the enhancement in mechanical properties of the syntactic foam while maintaining their low density. Compared with the coupling agent approach, the facile one-step PDA coating was much more effective. The failure mechanisms of the CNFs reinforced syntactic foam (CNFRSF) and the syntactic foam containing treated hollow microspheres were discussed in detail.