Publications

Rhodanine modified graphene for high-performance elastomer/graphene composites.

Incorporating dynamic covalent bonds (DCBs) into elastomers provides a seminal solution for the upcycling of traditional thermoset elastomers. Recently, engineering a multiphase network with various cross-linking uniformity and phase structures has been proven to be an effective strategy to overcome the bottleneck of continuous and high-throughput recycling (e.g., extrusion reprocessing) of vitrimeric elastomers. However, all of the relevant studies only focused on revealing the influences of network structures on the macroscopic properties of the systems. As for the microscopic mechanism of the multiphase network at the molecular level, it is still lacking. Herein, based on coarse-grained molecular dynamics (CGMD) simulation, a modeled DCBs-cross-linked elastomer with a multiphase network was established, which was subsequently subjected to in situ tensile or shear forces to simulate the evolution of local chain segment motion and stress/strain distributions in various microregions of the network under the complex extrusion/injection force field. The results indicate that phase domains with different cross-link densities feature distinct chain segment motion behavior and local stress/strain distribution evolution during tensile/shear deformation, and the interfacial phase exhibits significant high stresses. Therefore, incorporating heterogeneously cross-linked multiphase networks into elastomeric vitrimers can enable the system to have significant network reinforcement and unique interfacial stress amplification effects, which are critical for determining extrusion/injection reprocessability. Therefore, we envisage that the present study can provide a molecular-level theoretical explanation for the extrusion/injection reprocessability of multiphase elastomeric vitrimers, thereby guiding the rational network/performance design of these seminal materials.

Fully dense ceramic–carbon-nanotube composites with homogeneously distributed multiwalled carbon nanotubes (MWCNTs) (see Figure; inset shows a single MWCNT) have been synthesized by a unique method, which uses a polymer-derived ceramic as the composite matrix. Composites with an MWCNT fraction of 6.4 vol.-% had significantly increased Young's moduli, hardness, and damage resistance, compared to the values for the pure ceramic matrix.

The development of an efficient and low-cost electrocatalyst is critical to the hydrogen evolution reaction (HER). Herein, we reported a Ru@Cr3N0.4C1.6 nanoparticles grown on carbon nanofibers, which was prepared by electrospinning and high temperature carbonization strategies. The introduction of Ru metal helps Cr3N0.4C1.6 nanoparticles expose active sites on the surface of CNF to improve the catalytic performance, while the introduction of Cr optimizes the binding energy of Ru-H to achieves higher catalytic activity. Moreover, the heterogeneous structure formed by Ru metal and Cr3N0.4C1.6 nanoparticles also contributed to the catalytic performance. Therefore, the Ru@Cr3N0.4C1.6/CNF exhibited excellent catalytic activity with a low overpotential of 35 mV to obtain current density of 10 mA cm−2 in 1 M KOH. And it also showed outstanding long-term stability after continuously working for 200 h. This work provides a new method to prepare catalysts efficiently and cheaply.

Layered inorganics are promising in the fabrication of elastomeric nanocomposites with enhanced barrier property. Recently, boehmite (BM) nanoplatelets have emerged as alternative layered inorganics to clays and double hydroxylates as the functional reinforcement for rubbers. In the present paper, natural tannic acid (TA) is introduced as a novel interfacial modifier in BM-filled styrene–butadiene rubber (SBR) nanocomposites. The modification mechanism and interfacial interactions in the nanocomposites are fully characterized. Due to the strengthened interface and the comparatively finer dispersion state of BM in the nanocomposites, significantly enhanced mechanical properties are found in the modified system. At higher BM loadings (higher than 40phr), the modified system possesses a much lower gas permeability compared with the unmodified counterpart. Very interestingly, the TA-modified SBR/BM nanocomposites exhibit high tensile strength yet impressively low moduli compared with previously reported rubber nanocomposites filled with other nanofillers.

Abstract Couplant is indispensable for ultrasound examinations. However, shape adaptability and operational feasibility, which are both crucial, cannot be provided conjointly by existing couplants due to their either liquid or solid form. Here an ideal couplant composed of fibers and dynamically cross‐linked polysilicone is reported, which exhibits a unique solid‐to‐fluid transition upon application of stress exceeding a threshold. Together with the acoustically transparent feature, the particularity of the stress‐triggered fluidity allows conformal adapting to arbitrary geometries under stress exertion and stable preserving for long‐term and reliable ultrasound examination after stress release. Steeply curved geometries and pressure‐sensitive tissues, which are extremely challenging for the state‐of‐the‐art ultrasound modalities, are successfully graphed or treated. This couplant integrates the merits of liquids and solids, providing new opportunities for various ultrasound in industrial and medical fields.

Many recycled plastics are the polypropylene (PP)/poly(ethylene terephthalate) (PET) blends with PET as the minor component. The modification of such kinds of PP/PET blends for higher performance is essential as PP and PET are not thermodynamically compatible. In this study, the elastomer, SEBS‐ g ‐MAH, and the inorganics, halloysite nanotubes (HNTs) are chosen as the modifiers for the modification of a model PP/PET blend (90/10). The mechanical performance of such blend is optimized by the selective dispersion of the nanotubular HNTs into the interfacial region of the blends via a two‐step process. Compared with the control one, the overall mechanical properties of the blend are substantially improved. The crystallization of PP in the blend is also facilitated by the selective dispersion of HNTs and the folding surface free energy is substantially increased. The substantially improved mechanical performance is interpreted according to the formation of the unique morphology. This study provides new insight in improving the performance of polymer blends via selectively dispersing the nanosized inorganics in the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The problems of high volatile organic compound (VOC) emission and low efficiency of silane coupling agents (SCAs) used in the rubber/silica composites for "green tires" have been troubling the rubber industry. A unique silane (MFSi) integrating hydroxyls, tertiary nitrogen, and norbornenyl were prepared by a solvent-free/catalyst-free one-pot method. MFSi can graft onto the rubber chain through a highly efficient norbornenyl/sulfur reaction, while the dangling hydroxyls in MFSi can improve its affinity with silica and tertiary nitrogen has a significant internal catalytic effect on the silanization of silica. As a result, MFSi shows a significantly higher coupling efficiency of silica-filled composites compared to the most widely used SCAs. Consequently, MFSi-modified composites exhibit excellent environmental friendliness, including significantly reduced heat buildup (∼55%) and abrasion loss (∼53%) and VOC emissions (∼42%). We envision that the design of the multifunctional mediator will provide valuable insights into the development of high-performance "green tires" in a more environmentally friendly manner.

In polymer composites, filler dispersion and interfacial adhesion are two critical factors in determining their properties. To date, it still remains a challenge to achieve uniform filler dispersion and implement interfacial tailoring in rubber composites by direct melt mixing. In this study, we prepared graphene oxide (GO) slurry in acetone via a simple solvent exchange method and modified GO in the slurry. Then the slurry was compounded with nitrile rubber on two-roll mill to produce composites. Morphological and interfacial structural studies revealed that GO was dispersed at nano-scale in the composites, and the dispersion of GO and interfacial adhesion were further improved upon the modification of GO with silane. Consequently, the mechanical properties of the composites were remarkably enhanced by adding GO.

The functionalized graphene (JTPG) is fabricated by chemical conversion of graphene oxide (GO), using tea polyphenols (TP) as the reducer and stabilizer, followed by further derivatization through the Mannich reaction between the pyrogallol groups on TP and Jeffamine M-2070. JTPG exhibits solubility in a broad spectrum of solvents, long-term stability and single-layered dispersion in water and organic solvents, which are substantiated by AFM, TEM, and XRD. The paper-like JTPG hybrids prepared by vacuum-assisted filtration exhibits an unusual combination of high toughness (tensile strength of ~275 MPa and break strain of ~8%) and high electrical conductivity (~700 S/m). Still, JTPG is revealed to be very promising in the fabrication of polymer/graphene composites due to the excellent solubility in the solvent with low boiling point and low toxicity. Accordingly, as an example, nitrile rubber/JTPG composites are fabricated by the solution compounding in acetone. The resulted composite shows low threshold percolation at 0.23 vol.% of graphene. The versatilities both in dispersibility and performance, together with the scalable process of JTPG, enable a new way to scale up the fabrication of the graphene-based polymer composites or hybrids with high performance.

The effects of secondary particle size distribution on the electromagnetic properties of the carbonyl iron powder cores have been investigated in this work. For preparing the cores, the iron powders were firstly undergone insulation treatments including phosphorization and organic coating. After granulation, the secondary particles with different size distributions were molded into the final shape and cured at 200 °C. The results show that for the secondary particles with unimodal size distribution, the real part of the complex magnetic permeability of the powder core is in inverse proportion to the particle size. For the cores prepared from the secondary particles with bimodal size distribution, the effects of the size ratio and volume ratio of the coarse particle/fine particle on the magnetic properties are discussed. It is found that the permeability increases with the increasing volume of fine secondary particles. The minimum magnetic loss factor value is obtained at the coarse/fine secondary particles volume ratio of 7:3. The density and magnetic properties including complex permeability and magnetic loss of the cores prepared with coarse/fine particles size ratio of ~3 and ~7 are both in inverse proportional to the volume fraction of coarse secondary particles. The present work indicates that a reasonable size distribution of the secondary particles is required to improve the magnetic properties of the soft magnetic powder cores.

It remains a huge challenge to create advanced elastomers combining high strength and great toughness. Despite enhanced strength and stiffness, elastomeric nanocomposites suffer notably reduced extensibility and toughness. Here, inspired by the concept of sacrificial bonding associated with many natural materials, a novel interface strategy is proposed to fabricate elastomer/graphene nanocomposites by constructing a strong yet sacrificial interface. This interface is composed of pyridine-Zn(2+) -catechol coordination motifs, which is strong enough to ensure uniform graphene dispersion and efficient stress transfer from matrix to fillers. Moreover, they are sacrificial under external stress, which dissipates much energy and facilitates chain orientation. As a result, the strength, modulus, and toughness of the elastomeric composites are simultaneously strikingly enhanced relative to elastomeric bulk. This work suggests a promising methodology of designing advanced elastomers with exceptional mechanical properties by engineering sacrificial bonds into the interface.

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