N anocomposites have attracted wide attention because of their potential to combine desirable properties of different nanoscale building blocks to improve mechanical, optical, electronic , or magnetic properties. 16 Most traditional synthesis approaches of nanocom-posites rely on mechanical or chemical mixing and produce a random distribution of the constitutive phases. To address these problems, several groups recently investigated layer-by-layer deposition and other techniques to prepare layered nanocom-posites with ceramics, clays, and graphite oxide nanoplatelets, 79 but these methods are lacking in nanoscale spatial precision and are time-consuming and difficult for bulk-materials synthesis. On the other hand, biological systems abound with nanocom-posites that possess well-controlled archi-tectures based on multiple scale and multi-functional building blocks. 10 One powerful approach to achieve similar control is to use amphiphilic polymer or surfactant to direct the self-assembly of nanostructured metal oxides, semiconductors, and polymer materials. 1115 There has been a growing interest in incorporating functional components , such as functional groups, polymers, and nanoparticles, into the self-assembled nanostructures, but success has been limited to two-phase organic/inorganic hybrid materials, nanoparticles, or polymer-based nanocomposites. 4,5,16,17 Recently, a range of nanoscale building blocks, including carbon nanotubes 1821 and graphene, 2224 have gained prominence. Graphene and graphene stacks (mul-tilayer graphene), potentially low cost alternative materials to single-wall or multiwall carbon nanotubes, have unique electronic conductivity and mechanical properties. 2527 Graphene-based nanocom-posites with polymer, metal, or metal oxides have also shown unique mechanical, electronic , and electrochemical properties. 23,2835 We focus on the nano-composites made of metal oxides (i.e., SnO 2 , NiO, MnO 2 , and SiO 2) that could have important applications for electrochemical energy storage. 36,37 The low conductivity and poor stability of such materials usually necessitate adding conductive phases to enhance electron transport and electrical contact of the active materials in the electrode of a Li-ion battery. In most of these studies, the approach used to prepare the composite materials has been mechanical mixing of metal oxides with conductive materials such as amorphous carbon, carbon nano-tubes, and graphene. 31,38 In spite of these studies, a well-controlled architecture of the conductive material and metal oxide is difficult to achieve because of improper ABSTRACT Surfactant or polymer directed self-assembly has been widely investigated to prepare nanostructured metal oxides, semiconductors, and polymers, but this approach is mostly limited to two-phase materials, organic/inorganic hybrids, and nanoparticle or polymer-based nanocomposites. Self-assembled nanostructures from more complex, multiscale, and multiphase building blocks have been investigated with limited success. Here, we demonstr...

Although lithium-sulfur (Li-S) batteries are promising next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfide shuttling. These problems can be mitigated through the use of single-atom catalysts (SACs), which exhibit the advantages of maximal atom utilization efficiency (≈100%) and unique catalytic properties, thus effectively enhancing the performance of electrode materials in energy-storage devices. This review systematically summarizes the recent progress in SACs intended for use in Li-metal anodes, S cathodes, and separators, briefly introducing the operating principles of Li-S batteries, the action mechanisms of the corresponding SACs, and the fundamentals of SACs activity, and then comprehensively describes the main strategies for SACs synthesis. Subsequently, the applications of SACs and the principles of SACs operation in reinforced Li-S batteries as well as other metal-S batteries are individually illustrated, and the major challenges of SACs usage in Li-S batteries as well as future development directions are presented.

An advanced elastomer was developed by incorporating a dual-dynamic network into cis-polyisoprene, which combines excellent mechanical properties with high self-healing capability.

Coarse-grained molecular dynamics simulations were performed to investigate the mobility of nanoparticles (NPs) embedded in end-linked polymer networks, considering both the entangled and unentangled cases. For the entangled case, where the network strand length N x is longer than the entanglement length N e , the strand dynamics exhibits a heavily entangled subdiffusive feature before being restricted within the fluctuation distance d fluct by the permanent cross-links. The dynamics of NPs with size d NP smaller than the entanglement tube length d T in such network follows the same behavior as that in entangled linear polymers, while for NPs with size comparable to d T , their motion is suppressed by the entanglements. The constraint release of the entanglements would allow the particles to pass through but is slightly restricted by the permanent network junctions. For the unentangled case, where N x / N e < 1, the network strands can move only locally with suppressed subdiffusive behavior due to the restrictions imposed by the adjacent network junctions. Consequently, the coupled NP dynamics is also reduced. In addition, when d NP is larger than the strand fluctuation distance d fluct , the NPs are trapped by the network cages and can diffuse at long times through hopping, which is partially masked by the NP thermal fluctuations, as reflected from the NP trajectories. Such hopping fashion of NP motion becomes more apparent with increasing the network confinement ratio before being permanently localized within the network. Increasing the NP− polymer attraction would further hamper the NP mobility. In general, this work provides some insights into understanding how the permanent cross-links affect the network dynamics and thereby the coupled NP mobility.

No abstract

In this article, we report the enhanced anti‐aging and mechanical properties of waterborne polyurethanes (WPUs) modified by lignin amines, which were prepared from lignins, formaldehyde, and diethylenetriamine via a Mannich reaction. When we introduced amino groups into the lignin, its solubility in water and reactivity with isocyanate was obviously improved. Consequently, the interaction between WPU and the lignin additive were promoted; this provided a higher mechanical performance, that is, a higher tensile strength and elongation at break. More importantly, the intrinsic antioxidative activity of lignin also benefitted the modified WPU in terms of aging resistance. According to artificial accelerated aging tests, mechanical measurement, attenuated total reflectance–Fourier transform infrared spectroscopy, and scanning electron microscopy analysis, the lignin amine modified WPU did not show any evidence of degradation after 2 months of artificial accelerated aging, whereas the pure WPU was obviously degraded. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1736–1742, 2013

No abstract

Through coarse-grained molecular dynamics simulations, we have studied the effects of grafting density (Σ) and grafted chain length (Lg) on the structural, mechanical and visco-elastic properties of end-grafted nanoparticles (NPs) filled polymer nanocomposites (PNCs). It is found that increasing the grafting density and grafted chain length both enhance the brush/matrix interface thickness and improve the dispersion of NPs, but there seems to exist an optimum grafting density, above which the end-grafted NPs tend to aggregate. The uniaxial stress-strain behavior of PNCs is also examined, showing that the tensile stress is more enhanced by increasing Lg compared to increasing Σ. The tensile modulus as a function of the strain is fitted following our previous work (Soft Matter, 2014, 10, 5099), exhibiting a gradually reduced non-linearity with the increase of Σ and Lg. Meanwhile, by imposing a sinusoidal external shear strain, for the first time we probe the effects of Σ and Lg on the visco-elastic properties such as the storage modulus G', loss modulus G'' and loss factor tan δ of end-grafted NPs filled PNCs. It is shown that the non-linear relation of G' and G'' as a function of shear strain amplitude decreases with the increase of Σ and Lg, which is consistent with experimental observations. We infer that the increased mechanical and reduced non-linear visco-elastic properties are correlated with the enhanced brush/matrix interface and therefore better dispersion of NPs and stronger physical cross-linking. This work may provide some rational means to tune the mechanical and visco-elastic properties of end-grafted NPs filled polymer nanocomposites.