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The energy release performance of energetic compounds like 3-nitro-1,2,4-trizole-5-one (NTO) and 5,5′-bistetrazole-1,1′-diolate (TKX-50) are indispensable in propellent formulations. However, thermal decomposition behavior is impeded by unfavorable catalysts. Presently, ultrathin porous MoS2 nanosheets (pMoS2) are considered as high-performance catalysts for NTO and TKX-50 decomposition. The pMoS2 in 5 wt% content could decrease the decomposition temperature of NTO and TKX-50 by 13.5 °C and 37.1 °C, respectively. Furthermore, the exothermic heat-release for pMoS2@NTO and pMoS2@TKX-50 were increased almost by a factor of two. The porous structure combined with large specific area of pMoS2 could mostly trigger the catalytic effect towards energetic compound decomposition. Additionally, the as-obtained MoS2 endowed advances in safety performance of NTO and TKX-50, with remarkably reduced impact and friction sensitivity. The as-proposed strategy may stimulate a different perspective towards the fast decomposition of energetic materials in propellants. [ABSTRACT FROM AUTHOR]

Inspired by the strong chemical adhesion of mussels, the polymerization of dopamine was first introduced to coat energetic organic crystals through a simple immersion method. 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane (HMX) was used as substrate. In-depth characterizations confirmed a compact core–shell formation with a dense graphite-like structure PDA on every HMX crystal. The phase transition temperature of the crystals (β phase → δ phase) was improved by 27.5 °C for HMX enabled in 0.5 wt% PDA. In situ XRD showed that 94.8% of β-HMX was transformed to δ-HMX, whereas only 14.7% of β-HMX was transformed in HMX with 2.1% PDA at 210 °C. The heated HMX/PDA crystals (210 °C, 30 min) retained primary morphology, with intact PDA shell, demonstrating the excellent ability of PDA to prevent thermal damage in energetic crystals. The impact sensitivities of HMX and HMX/PDA were tested by Bundesanstalt für Materialprüfung (BAM) method. No difference between HMX (impact energy: 5.0 J) and HMX/PDA (5.0 J) at room temperature was attributed to the rigid PDA shell, which was benefit for phase transition, but inefficient for reducing sensitivity. After being heated at 200 °C for 30 min, the impact energy of HMX showed a dramatically drop (2.0 J), while that of HMX/PDA unchanged (5.0 J), indicating the increased sensitivity of HMX after thermal damage, and retardation of phase transition is benefit for the safety of polymorph explosives. This work demonstrates the successful application of dopamine chemistry to energetic materials, thereby providing a potential method for the modification of energetic crystals. [ABSTRACT FROM AUTHOR]

We analyze the effect of targeted informative advertising on firms' incentive to improve product quality and the welfare implications. We find that, compared with mass advertising, targeted advertising results in (i) a decreased incentive to invest in R&D unless the cost of advertising is sufficiently low, (ii) a lower mark-up, net of product quality, being charged to consumers, and (iii) a smaller (larger) proportion of uninformed consumers when the cost of advertising is low (high). The firms may earn higher or lower profits, but consumers are usually better off due both to the lower net mark-up and to improved product-consumer match. Under certain conditions though, the negative impact of more uninformed consumers dominates and leads to reduced consumer and total welfare. • The effect of targeted informative advertising in the presence of R&D rivalry is analyzed. • It results in a decreased the incentive for R&D unless advertising cost is sufficiently low. • Endogenous R&D expands the range in which targeted advertising benefits the firms. • Consumers usually benefit from lower net mark-up and better product-consumer match. • It is possible that consumer and total welfare decrease relative to mass advertising. [ABSTRACT FROM AUTHOR]

. In this paper, we introduce stochastic R&D into a Hotelling model with two duopolists. With an emphasis on the interaction between firms' R&D decision and location choice, we compare socially and privately optimal locations and levels of R&D. We show that, depending on R&D cost and the degree of technical risk, equilibrium location varies from minimum differentiation to maximum differentiation. From a welfare perspective, the equilibrium distance between the two firms could be either closer, farther or socially best. Moreover, depending on cost structure, firms' R&D expenditures could be either higher, lower or socially optimal, from a welfare viewpoint. [ABSTRACT FROM AUTHOR]

Abstract: The platelet derived growth factor receptor (PDGFR) is an important target for novel anti-cancer therapeutics, but agents targeting PDGFR have been associated with cardiotoxicity. Cardiomyocyte PDGFR-β signaling in pressure-overloaded hearts induces compensatory angiogenesis via a paracrine-signaling cascade. Tight regulation of receptor tyrosine kinases in response to ligand stimulation is a critical part of any such cascade. The objective of the present study was to characterize the early and late regulation of PDGFR-β following ligand stimulation and define a potential role for microRNAs (miRNAs) predicted to interact with the 3′UTR of PDGFR-β in feedback regulation. Using two in-vitro model systems (U87 glioblastoma cells and neonatal cardiomyocytes), we observed that in response to stimulation with PDGF-BB, levels of PDGFR-β declined beginning at one hour, persisting for 48h. PDGFR-β mRNA levels declined beginning at 6h after receptor activation. Early, but not late activation-induced receptor downregulation was proteasome dependent. Levels of miRNA-9 (miR-9) were significantly increased in U87 cells and cardiomyocytes beginning 6h after addition of ligand. In response to pressure overload, miR-9 levels were significantly reduced in the hearts of cardiac-specific PDGFR-β knockout mice. Luciferase reporter assays demonstrate that miR-9 directly interacts with its predicted seed in the 3′UTR of PDGFR-β. Increasing miR-9 levels reduces levels of PDGFR-β, resulting in a reduction in the paracrine angiogenic capacity of cardiomyocytes, consistent with the established function of cardiomyocyte PDGFR-β. Importantly, increase of anti-miR-9 in cardiomyocytes attenuates ligand-induced PDGFR-β downregulation. In conclusion, we have identified miR-9 as an activation-induced regulator of PDGFR-β expression in cardiomyocytes that is part of a negative feedback loop which serves to modulate PDGFR-β expression upon ligand-stimulation through direct interaction with the 3′UTR of PDFGR-β. This article is part of a Special Issue entitled ‘Possible Editorial’. [Copyright &y& Elsevier]

Background: Repetitive deformation stimulates proliferation in human Caco2 intestinal epithelial cells by way of an ERK1/2-dependent pathway. We examined the effects of cytoskeletal perturbation on deformation-induced signaling in Caco2 cells.Methods: The Caco2 cell cytoskeleton was disrupted with either cytochalasin D, phalloidin, colchicine, or paclitaxel. Levels of alpha-actinin-1 and -4 and paxillin were reduced by specific small interfering RNA. Cells on collagen I-precoated membranes were subjected to 10% repetitive deformation at 10 cycles/min. After 1 hour, cells were lysed for Western blot analysis.Results: Strain-activated ERK1/2, focal adhesion kinase, and Src phosphorylation in dimethyl sulfoxide- and/or nontargeting small interfering RNA-treated control cell populations. Cytochalasin D and paclitaxel, but not phalloidin and colchicine, blocked ERK1/2 phosphorylation. A decrease in alpha-actinin-1, but not in alpha-actinin-4 or paxillin, inhibited ERK1/2 and focal adhesion kinase phosphorylation, whereas Src activation appears to be independent of these effects.Conclusions: The intestinal epithelial cell cytoskeleton may transduce mechanical signals by way of alpha-actinin-1 into the focal adhesion complex, culminating in ERK1/2 activation and proliferation. [ABSTRACT FROM AUTHOR]

Abstract: Background: Repetitive deformation stimulates proliferation in human Caco2 intestinal epithelial cells by way of an ERK1/2-dependent pathway. We examined the effects of cytoskeletal perturbation on deformation-induced signaling in Caco2 cells. Methods: The Caco2 cell cytoskeleton was disrupted with either cytochalasin D, phalloidin, colchicine, or paclitaxel. Levels of α-actinin-1 and -4 and paxillin were reduced by specific small interfering RNA. Cells on collagen I–precoated membranes were subjected to 10% repetitive deformation at 10 cycles/min. After 1 hour, cells were lysed for Western blot analysis. Results: Strain-activated ERK1/2, focal adhesion kinase, and Src phosphorylation in dimethyl sulfoxide- and/or nontargeting small interfering RNA-treated control cell populations. Cytochalasin D and paclitaxel, but not phalloidin and colchicine, blocked ERK1/2 phosphorylation. A decrease in α-actinin-1, but not in α-actinin-4 or paxillin, inhibited ERK1/2 and focal adhesion kinase phosphorylation, whereas Src activation appears to be independent of these effects. Conclusions: The intestinal epithelial cell cytoskeleton may transduce mechanical signals by way of α-actinin-1 into the focal adhesion complex, culminating in ERK1/2 activation and proliferation. [Copyright &y& Elsevier]

Diverse repetitive forces deform the intestinal epithelium and basement membrane. Such repetitive deformation induces intestinal epithelial proliferation, differentiation, and intracellular signaling. Although at least some deformation-induced signals probably involve integrins, the matrix-dependence of these signals is poorly understood. We compared rapid strain activation of p38 and jnk in human Caco-2 intestinal epithelial cells cultured on collagen I, collagen IV, laminin, and tissue fibronectin. These signals were inhibited in cells on a fibronectin substrate, but activated by strain on collagens and laminin. Furthermore, adding 300 μg/ml plasma fibronectin (approximately the concentration found in plasma) to the culture medium inhibited strain activation of p38 and jnk in cells cultured on collagen. Since tissue and plasma fibronectin levels vary in acute or chronic inflammatory or infectious conditions, these results suggest that tissue or plasma fibronectin may modulate the intestinal epithelial response to repetitive deformation. [Copyright &y& Elsevier]

Docosahexaenoic acid (DHA) and butyrate favorably modulate colonocyte proliferation and apoptosis. In order to elucidate how oncogenic Ras modulates responses to these chemopreventive nutrients, we incubated isogenic non-transformed and Ras malignant transformed mouse colon cells with butyrate and DHA or linoleic acid (LA). Combining DHA with 1 mM butyrate decreased proliferation relative to LA or no PUFA treatment in both cell lines. At a higher butyrate dose (5 mM), caspase 3 activity was elevated to a greater extent in Ras transformed cells. Only non-transformed cells were sensitive to the apoptogenic effects of DHA, indicating that Ras transformation alters sensitivity to dietary chemopreventive agents. [Copyright &y& Elsevier]

Alterations in ATP production, intracellular energy levels and mitochondrial function have been shown to trigger cytokinetic events in vitro, including inhibition of cell division, abnormal or blocked differentiation and inhibition of apoptosis. Changes in colonic cytokinetics are directly related to colon tumorigenesis but alterations in energy metabolism during the tumorigenic process have never been reported. We conducted a 2 x 2 x 3 factorial design study in 120 male Sprague-Dawley rats with two diets (pectin or cellulose-supplemented), two injected subgroups (with or without the carcinogen azoxymethane, AOM) and three termination time points (6, 16 and 36 wk post-second injection). Colonocytes were isolated and incubated with their primary energy substrates (radiolabeled butyrate, glucose, glutamine and beta-hydroxybutyrate) for 60 min. Production of lactate, ketone bodies and CO2 were determined. At 6 wk, there were no significant differences in metabolism among treatments. In contrast, at 16 wk, AOM-injected rats had dramatically lower rates of CO2 production (P < 0.001) from both glucose and butyrate and lower rates of lactate and ketone body production than their saline counterparts. At 36 wk, when tumors developed, the depressed production of lactate and ketone bodies seen in AOM-injected rats at 16 wk returned to control values. However, in AOM-injected rats, CO2 production from glucose and butyrate remained depressed. Cellulose feeding resulted in decreased oxidation of glucose, butyrate and glutamine and an increased production of ketone bodies from butyrate by colonocytes compared with pectin feeding at 36 wk. We conclude that colonocyte energy metabolism differs in AOM-injected rats vs. saline controls and changes during tumorigenesis, and suggest a relationship between intracellular energy status and changes in cell kinetics. This is the first report that such a relationship may exist in vivo. [ABSTRACT FROM AUTHOR]

1,3,5-Trinitro-1,3,5-triazinane (RDX) has attracted considerable attention in energy-related fields. However, the safety performance of RDX needs to be improved in terms of various external stimuli. Herein, such issues of RDX could be well balanced through hydrothermal assembly with the assistance of insensitive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in a low content of 10 wt% (named RT co-particles). The TATB spread outside and were embedded inside of the resultant RT co-particles, which were examined via X-ray computed tomography and a three-dimensional laser scanning confocal microscope. As a result, the impact safety performance of RT co-particles could be drastically enhanced to 17.5 J by the TATB lubricant effect, demonstrating over twice the value of that of raw RDX (6 J) and mixtures (7 J). Moreover, an interfacial reconstruction between RDX and TATB was witnessed due to the strong interfacial interaction, as examined by theoretical simulation. Inspired by this, a delayed exothermic decomposition temperature of RT co-particles (244.4 °C) has been achieved when compared with that of RDX (241.4 °C). As demonstrated, an energetic co-particle strategy may provide an effective pathway toward remarkably improved mechanical and thermal safety performance, shedding light on other energetic materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Theoretical simulation was employed to select suitable conductive polymers for coating. • Three HMX/conductive polymer based composites were facilely prepared by in-situ polymerization. • The synergistic desensitization of impact and electrostatic spark was obtained. • Improved thermal phase stability with sluggish phase-transition kinetics was confirmed. Safety performance under external stimuli plays a crucial role for energetic materials. Therefore, desensitization of high explosive arouses widespread research interests in the field of energetic materials. Nevertheless, synergistically reducing impact and electrostatic spark sensitivities of 1,3,5,7-tetranittro-1,3,5,7-tetrazocane (HMX) remains challenging. Herein, a novel strategy concerning conductive polymer coating was proposed to solve this issue. Theoretically, the polypyrrole (PPy) can form a complete shell and strong interaction with HMX crystals. The HMX@PPy composite has been successfully achieved by in-situ polymerization, exhibiting superior sensitivities (impact: from 7 J to 27.5 J and electrostatic spark: from 0.4 J to 1.68 J) among reported HMX-based energetic materials. In addition, the thermal phase stability of HMX can also be visibly improved with sluggish phase-transition kinetics by introducing PPy coating. The current study provides a design concept for high energy explosives with low sensitivity and improved comprehensive performances. [ABSTRACT FROM AUTHOR]

Self-healing polymeric materials have attracted considerable interests due to the capability of healing the cracks generated in functional materials autonomously, resulting in improved reliability and life cycle. This paper is intended to develop a self-healing polymeric binder for energetic composites by incorporation of reversible covalent bonds into polyurethane. A novel polyurethane was synthesized from NCO-terminated prepolymer with furfuryl amine, and cross-linked with bismaleimide via Diels-Alder (DA) reaction. The chemical structures of the intermediates and products of Diels-Alder polyurethane (DAPU) were firstly confirmed by nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Then, the thermal reversibility and the self-healing performances of DAPU based energetic composites were systematically studied by DSC, polarizing optical microscopy (POM) and tensile testing. All the results showed that the as-prepared DAPU had high self-healing efficiency and remarkable mechanical performance, providing potential applications as a promising self-healing material in repairing the cracks generated in energetic composites. • Self-healing polymeric binder with Diels-Alder bonds can be easily synthesized. • The as-prepared Diels-Alder polyurethane has perfect self-healing properties. • The self-healing polyurethane has stronger mechanical properties than commercial polyurethane. • Energetic composites contained self-healing polyurethane exhibit evidently high self-healing capability. • The self-healing energetic composites present remarkable mechanical performance. [ABSTRACT FROM AUTHOR]

The development of a facile method for improvement of interface interaction between rigid particles and coating polymer is of great importance for energetic composite materials, especially for military purpose. In this paper, energetic composites with spherical morphology, toughness property and low sensitivity are firstly fabricated by using Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) as core material and thermoplastic polyester-ether elastomer (TPEE) as shell material via an emulsion solvent evaporation (ESV) method. From the morphology and structure characteristic of as-prepared energetic microspheres, it is found that the HMX@TPEE energetic microspheres have uniform spherical morphologies, narrow size distribution and honeycomb coating structure under the circumstance of compound emulsifiers and appropriate core-shell ratio. The good toughness of HMX@TPEE microspheres in Brazilian test and dynamic mechanical analysis (DMA) demonstrates a new route to enhance interface interaction between HMX particles and TPEE matrix. Moreover, because of the favorable energy-decentralizing property of this exotic honeycomb structure, the sensitivity of HMX@TPEE microspheres measured by BAM impact sensitivity instrument can be markedly decreased and the impact energy ( E li ) can be improved from 3.5 J to 8.0 J at the HMX/TPEE ratio of 5/1. This fabrication of HMX@TPEE microspheres with adjustable coating content via a facile ESV process might provide a promising approach for HMX based energetic composites to enhance the safety and toughness properties when used in advanced weapon system. [ABSTRACT FROM AUTHOR]

A phase manipulation of molybdenum disulfide strategy has been adopted for fast decomposition of AP and HMX with safety operation performance. • Li-ion assisted manipulation of MoS 2 made it into highly active 1T phase. • 1T-MoS 2 possessed enhanced active sites, electrical conductivity and porosity. • Intrinsic lamellar MoS 2 improved safety performances of AP and HMX. • Fast energy releasing of HMX and AP was gained using 1T-MoS 2 catalyst. Designing advanced component for synergistically achieving the safety performance and energy releasing of widely studied energetic materials (EMs) is of far-reaching significance in composite solid propellants. Herein, molybdenum disulfide with high-active 1T phase (1T-MoS 2) was engineered by a phase-manipulation strategy through chemical Li-intercalation from its original state (2H-MoS 2). The as-prepared 1T-MoS 2 was used for the improved safety and decomposition performances of two typical EMs (ammonium perchlorate: AP and 1,3,5,7-tetranittro-1,3,5,7-tetrazocane: HMX) in propellants. Lubricant 1T-MoS 2 endowed considerable advances in safety performance of EMs, with remarkably reduced the impact and friction sensitivity. Besides, fast energy-releasing performance with visibly lower activation energy was realized for AP@1T-MoS 2 and HMX@1T-MoS 2. In addition, large decomposition heats were simultaneously achieved. Computational studies disclosed this improvement could be attributed to the multi-coupling effect arising from the promoted electron transfer capability, strong affiliations of catalyst/burning products and the abundant actives sites of 1T-MoS 2 phase. Our results demonstrate substantial improvements in the synergistical design of safe and fast-decomposed AP and HMX complex for solid propellants. [ABSTRACT FROM AUTHOR]

The interfacial strength usually plays a key role for exhibiting great effects on mechanical performances. In this work, typical energetic crystal 1,3,5-triamino-2,4,6-trintrobenzene (TATB) was firmly coated by the strong adhesion of polydopamine (PDA), then two HBPs with fatty and aromatic structure were grafted onto the surface of TATB, by using the hydroxyl groups of the PDA layer as secondary reaction platform. Four highly-loaded polymer based energetic composites (solid loading was 95%) were prepared with fluoropolymer binders as substrate. The results showed that the surface of grafted samples with 0.5 wt% HBP was more easily wetted by non-polar liquid. Improved storage modulus and creep resistance properties were exhibited in polymer bonded explosives (PBXs). The static mechanical properties of tensile and compressive strength were increased significantly by 26.5% and 19.8%, respectively, due to the strong interfacial reinforcement of HBPs. • Successfully grafting hyperbranched polyester to energetic crystal for the first time. • Mechanical properties of PBX effectively enhanced by hyperbranched polyester grafting. • Interfacial reinforcement strategy can be extended to other highly loaded composites. [ABSTRACT FROM AUTHOR]

The mechanical properties of composites are highly dependent on the interfacial interaction. In the present work, inspired by marine mussel, the adhesion between energetic crystals of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and polymer binders was improved. Three types of linear polymeric agents of glycidyl azide polymer (GAP), polyethylene glycol (PEG), and polytetramethylene ether glycol (PTMEG) were grafted onto TATB particles bridged through polydopamine (PDA) films. SEM images showed that 5% grafting contents could evidently form roughness shells on the surface. With a reinforcement at the interface produced by grafting shells, the mechanical properties of polymer-bonded explosives (PBXs) exhibited outstanding mechanical performance, especially for the PTMEG-grafting sample. Examined by the contact-angle test, the PTMEG-grafting sample possessed a value of polar component similar to that of fluoropolymer, leading to an excellent wettability of the two phases. Additionally, different contents of PTMEG were grafted to reveal that the mechanical properties could be improved even with content as little as 0.5 wt.% PTMEG. These results might highlight a correlation between interfacial interaction and macroscopic properties for mechanically energetic composites, while providing a versatile route of grafting on highly loaded composites. [ABSTRACT FROM AUTHOR]

Energetic co-crystallization has been extensively explored as an effective strategy to balance the energy and sensitivity of energetic materials. In the present study, CL-20/HMX co-crystals with high purity, uniform morphology, well-proportioned size distribution, compact internal structure and reduced sensitivity were fabricated by a solvent-induced self-assembling approach using corresponding nanoparticles as the basic units. Such a CL-20/HMX co-crystal based on the self-assembly of a nano-explosive has been reported for the first time, providing a novel, high-yield, general and easily scaled-up method for the fabrication of energetic co-crystals. Notably, the formation processes of the as-synthesized co-crystals were determined as interfacial self-assembly at nanoparticle scale instead of the complete dissolution and nucleation process at the molecular level as observed with the traditional recrystallization technique. The completely formed CL-20/HMX co-crystal structure with few separate-assembled CL-20 or HMX crystals was charecterized by PXRD, TG-DSC, Raman, FT-IR, DG and SCXRD analyses. Additionally, the formation of intermolecular hydrogen bonds was confirmed by Terahertz (THz) analysis. The typical Avrami equation was constructed for modeling the kinetics of the assembly of CL-20/HMX co-crystals, and the self-assembly process can be generally summarized as the induction of nano-particles, oriented aggregation, surface integration and single co-crystal formation. [ABSTRACT FROM AUTHOR]

With the emergence and commercialization of graphene, new opportunities have emerged for toughening polymer‐based functional energetic composites (e.g., polymer‐bonded explosives [PBX]) using nano‐graphene without sacrificing strength and glass transition temperature, as compared with conventional elastomeric tougheners. In this work, inorganic nano‐graphene is used to study the toughness enhancing effects and mechanical properties of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX)‐based PBX. Fabrication procedures of HMX‐based PBX with different content of graphene are presented, and well‐dispersion for graphene in binder matrix is obtained by ultrasonic processing. Experimental results indicated the addition of nano‐graphene can greatly increase the toughness, with the fracture energy enhanced from 32.5 to 64.9 J m−3 compared with normal HMX‐based PBX. Such improvement was obtained at a low graphene concentration (0.2–0.4 wt%). Strong interaction of the graphene and the binder matrix, combined with the inherent properties of well‐dispersed graphene are the decisive factors with respect to the outstanding toughening effect. POLYM. COMPOS., 40:E1151–E1161, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The two‐dimensional graphene nanoplatelets (GNPs) were adopted to improve the mechanical behaviors of polymer bonded explosives (PBX). Five 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB)‐based PBX formulations without or with 0.05, 0.15, 0.5, and 1% GNPs by weight were prepared by the water suspension methods. The morphology and distribution of GNPs in PBX were investigated by a field emission‐scanning electron microscope and transmission electron microscope. The quasi‐static mechanical analysis of PBX by Brazilian and uniaxial compression tests revealed that the fracture strength and fracture strain were improved obviously with the addition of GNPs. The creep behaviors of neat PBX and modified PBX by GNPs were also investigated at different temperatures and stresses by the three‐point bending mode. The results indicated that, with the incorporation of only a small amount of GNPs, the creep resistance could be significantly improved due to the confinement effect of GNPs. Simultaneously, the creep behaviors were simulated using a six‐element mechanical model. The predicted theoretical results coincided quite well with the experimental data. At last, the effect of GNPs on the long‐term creep performance of PBX was predicted using the time‐temperature superposition principle. The modified PBX by GNPs showed consistently lower creep strain than the neat PBX in the entire time scale. POLYM. COMPOS., 39:3924–3934, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The one‐dimensional (1D) carbon nanotubes (CNTs) and two‐dimensional (2D) graphene nanoplatelets (GNPs) were adopted to enhance the thermal conductivity (K) of polymer‐bonded explosives (PBX). Seven 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB)‐based PBX formulations without or with 1.31 vf % carbon materials were designed and fabricated. The results indicated that, the K was only slightly improved by pure GNPs or CNTs. However, a remarkable synergetic effect between GNPs and CNTs in improving the K of PBX was demonstrated. The K of PBX with hybrid GNPs and CNTs was obviously higher than that of PBX with pure GNPs or CNTs. The bridging interactions between GNPs and CNTs could lead to the formation of a more efficient 3D percolating network. Moreover, the presence of CNTs triggered the percolation effect in the GNPs as the enhanced K was more pronounced with increasing GNPs. Additionally, the nonlinear dependence of the K of PBX on GNPs content was fitted by an analytical model which incorporated the percolation effect. The theoretical results were found to be in reasonably good agreement with the experimental data. Finally, the thermal shock resistance of PBX with hybrid CNT/GNP was significantly enhanced. POLYM. COMPOS., 39:E1452–E1462, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The interfacial interaction and the microstructure evolution play a vital role in the mechanical properties of thermoplastic polyurethane (TPU) based energetic composites. In this work, inspired by the strong adhesion of mussels, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) energetic crystals were coated with polydopamine (PDA) via in-situ polymerization of dopamine and then dispersed in TPU matrix. The core-shell structure of CL-20@PDA was confirmed by in-depth structural characterizations. The uniform and compact PDA shell gave rise to a high thermal stability with phase transition temperature of CL-20 crystals increased by 11.5 °C. Moreover, the PDA modification endowed the TPU based composites with excellent mechanical properties. A striking increase in mechanical properties and creep resistance was achieved with 6 h polymerization time of PDA. Compared with the PBX-Raw with untreated CL-20 crystals, the compressive and tensile strength after PDA coating increased by 115% and 57%, and the compressive and tensile fracture energy increased by 148% and 68%. The storage modulus at 25 °C was 40% higher than PBX-Raw. The enhancement effectivity could be ascribed to both interfacial interaction and the microstructure evolution of TPU binder. The theoretical simulations by molecular dynamics demonstrated the strong interfacial interaction mechanism between CL-20 and PDA. Moreover, the abundant hydrogen bonds between the hard segments of TPU and functional groups of PDA facilitated the formation of more hard microdomains which acted as physical crosslinking points to promote the phase separation. This work provides a potential method for the mechanical and thermal enhancement for TPU based energetic materials based on dopamine chemistry. Inspired by the strong chemical adhesion of mussels, the polymerization of dopamine was introduced to coat energetic crystals, which play a vital role in the interfacial interaction and the microstructure evolution of thermoplastic polyurethane (TPU) binder, resulted in mechanical and thermal enhancement for TPU based energetic materials. [Display omitted] • Core-shell structure was constructed through a novel, facile and general route via self-polymerization of dopamine. • CL-20@PDA composites exhibited 11.5 °C higher phase transition (ε.→γ) temperature than that of pure CL-20. • The mechanical enhancement was disclosed based on interfacial interaction and the microstructure evolution of TPU binder. • Theoretical simulations for the interfacial interaction showed good accordance with the experimental observations. [ABSTRACT FROM AUTHOR]

In this research, a group of segmented polyurethane (PU) copolymers with different hard segment (HS) contents were successfully synthesized. The microstructure of the PU copolymers was characterized via Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle neutron scattering (SANS). Then, the PU copolymers were selected as polymer binder for coating an insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) to prepare polymer bonded explosives (PBXs). When the HS concentration of PU copolymers increased from 14 to 34 wt %, a 14.6 times increase in the creep rupture time of PBXs under 60 °C/3 MPa and a 52.3% decrease in the steady-state creep strain rate under 60 °C/1 MPa were observed. The experimental results indicated that a wide variety of structure and properties of PU copolymer could be customizable through the adjustment of the HS contents, and consequently, provided an efficient route to tune the creep performance of the PBXs over a wide range. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) graphene nanoplatelets (GNPs) were adopted to enhance the thermal conductivity of PBX. The results indicated that, the thermal conductivity of PBX was only slightly improved with very low GNP loading (0.05 wt% and 0.15 wt%). However, a remarkable enhanced effect was observed at a relatively high GNP loading (0.5 wt% and 1 wt%). The thermal conductivity of PBX had a nonlinear dependence on the GNPs loading. The nonlinear dependence of the thermal conductivity on GNPs content was fitted by an analytical model which incorporated all the effects. And the thermal conduction mechanism of GNPs based composite could change from series thermal structure to parallel thermal structure with the GNP loading increasing. Additionally, the calculated thermal shock resistance and thermal stress distribution of PBX was both enhanced with the GNP loading. Finally, the sensitivity of sensitive hexanitrohexaazaisowurtzitane (CL-20) based PBX composition could be improved by GNPs due to enhanced thermal conductivity. [ABSTRACT FROM AUTHOR]

PDGFR is an important target for novel anticancer therapeutics because it is overexpressed in a wide variety of malignancies. Recently, however, several anticancer drugs that inhibit PDGFR signaling have been associated with clinical heart failure. Understanding this effect of PDGFR inhibitors has been difficult because the role of PDGFR signaling in the heart remains largely unexplored. As described herein, we have found that PDGFR-beta expression and activation increase dramatically in the hearts of mice exposed to load-induced cardiac stress. In mice in which Pdgfrb was knocked out in the heart in development or in adulthood, exposure to load-induced stress resulted in cardiac dysfunction and heart failure. Mechanistically, we showed that cardiomyocyte PDGFR-beta signaling plays a vital role in stress-induced cardiac angiogenesis. Specifically, we demonstrated that cardiomyocyte PDGFR-beta was an essential upstream regulator of the stress-induced paracrine angiogenic capacity (the angiogenic potential) of cardiomyocytes. These results demonstrate that cardiomyocyte PDGFR-beta is a regulator of the compensatory cardiac response to pressure overload-induced stress. Furthermore, our findings may provide insights into the mechanism of cardiotoxicity due to anticancer PDGFR inhibitors. [ABSTRACT FROM AUTHOR]

• Three energetic materials with distinctive nanoarray structures were facilely prepared by confined crystallization. • Markedly increased reactivity for thermal excitation, flame ignition and closed combustion was confirmed. • Improved safety performance and nice structural stability were obtained. • Two-component energetic nanoarrays consisted of interwoven fuels and oxidants showed excellent energy-release efficiency. For energetic materials (EMs), the crystal morphology, particle size and surface state have significant effects on their properties. Nano-sized EMs have attracted considerable research interests during the past decades because of their improved performances in ignition, combustion, and energy-release rate. In this work, several novel nanoarray-structured EMs have been prepared by a facile freeze-drying confined crystallization method, which is based on the self-assembly of materials during rapid recrystallization. The effects of reaction conditions on the morphology and structure of these EMs have been comprehensively studied using state-of-the-art techniques. Thermal decomposition kinetics was obtained from DSC data by Kissinger method. The mechanical sensitivity, ignition and combustion in a chamber with fixed volume were conducted. Such energetic crystal nanoarrays show typical one-dimensional morphology, with long aspect ratio and large specific surface area, some of which also have a distinctive fractal structure. Sensitivity results confirmed the visibly reduced impact and friction sensitivity of the energetic nanoarrays. Compared with normal energetic crystals, these as-prepared nanoarrays exhibited lower onset thermal decomposition temperature, higher ignition efficiency, and better combustion performance, particularly for the nanoarray of two-component composites containing both fuel and oxidizer. [ABSTRACT FROM AUTHOR]

Confinement of thermally conductive fillers is crucial for polymer based composites to achieve highly efficient filler-filler contact and construct conductive pathways. In order to obtain superior thermal conductivity, a novel strategy was proposed to construct separated architectures in energetic composites by selective distribution of graphene nanoplates (GNPs) in confined and continuous spaces. The thermal conductivity of the 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) @fluoropolymer (PF) @GNPs composites with incorporation of GNPs in separated architectures was markedly improved to 1.145 W/m K at a GNPs loading of 1.74 vol%, which was 197.2% higher than that of raw HMX@PF without GNPs. Theoretical simulation suggested that the enhanced thermal conductivity was mainly ascribed to the evidently reduced interfacial and contact thermal resistance. In addition, the characteristic impact energy (E BAM) was improved by 43% due to the good capability of heat dissipation, indicating improved safety performance for such energetic composites. This work provides a general and efficient strategy for the fabrication of high-performance energetic materials with high thermal conductivity, low sensitivity, and superior thermal shock resistance. [ABSTRACT FROM AUTHOR]

Damages generated in functional materials can deteriorate their performance and shorten their lifetime, endowing the materials with self-healing ability is expected to resolve this problem. In this work, a novel energetic composite refers to CL-20 based PBX, which can self-heal its mechanical damage under a mild condition, was designed and prepared via incorporating disulfide bonds into the polymeric binder. The highly efficient self-healing polyurethane-urea containing disulfide bonds (DSPU) was synthesized by using the prepolymer of poly(caprolactone) diol (PCL-diol) with isophorone diisocyanate (IPDI) as the main-chain to achieve good mechanical toughness, then cross-linking with bis(4-aminophenyl) disulfide (APD) to gain the superior reversibility. The CL-20 based PBX using this DSPU as binder can evidently self-heal its inner damage, i.e. micro-crack, after heating at 60 °C for several hours, and the strength of the damaged sample after Brazilian test can also be recovered to more than 70% of the pristine value. [ABSTRACT FROM AUTHOR]