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N-doped carbon-based materials are crucial electrically conductive additives and non-metal electrocatalysts for the oxygen reduction reaction. At present, many pieces of research are focused on the effects of micropore, mesopore and hierarchical pore structure on the catalytic activity, however, there are few works concerning the role of large-dimension through-hole structure. Hence, in this work, we prepare two kinds of carbon materials with large through-hole structure, i.e. N-doped carbon hollow-spheres and hollow-tubes, as the oxygen reduction catalysts. The synthesis follows template-free morphology-controlled pyrolysis, which is more convenient than the preparation of conventional N-doped nanotubes and graphene. The resultant N-doped carbon hollow-spheres and hollow-tubes evidently enhanced their ORR catalytic activity, remarkable long-term stability and methanol resistance. The large-dimension through-hole structure is found to account for the increase in mass transfer.
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The fascinating pulley effect from moveable α-cyclodextrin (α-CD) based polyrotaxane favors toughening of hydrogels, but the strategy is rarely applied in bulk polymers because of the severe aggregation trend of α-CDs. Herein, the authors propose a simple approach to moderately modify the α-CDs of polyrotaxane by introducing large steric side groups and reactive CC so as to minimize the unwanted hydrogen bonds-induced aggregation of α-CDs and hydrophilicity of polyrotaxane. Accordingly, the proof-of-concept material, poly(methyl acrylate) crosslinked by the modified polyrotaxane, turns out to be rather homogeneous with optical transparency. The polyrotaxane crosslinks are movable under external force as disclosed by in situ small-angle X-ray scattering and other techniques, which is correlated to the relative amount of α-CDs. A few polyrotaxane crosslinkers prove to be sufficient to simultaneously improve strength and toughness of poly(methyl acrylate) owing to the stress equalization. The present work provides an expandable toolbox for enhancing polymers.
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Ciclodextrinas , Rotaxanos , Hidrogéis , Interações Hidrofóbicas e Hidrofílicas , Polietilenoglicóis , PolímerosRESUMO
A quadrupole electric field-mediated exfoliation method is proposed to convert micron-sized hexagonal boron nitride (h-BN) powder into few-layer hexagonal boron nitride nanosheets (h-BNNS). Under optimum conditions (400 Hz, 40 V, 32 µg ml-1, sodium deoxycholate, TAE medium), the h-BN powders (thickness >200 nm, horizontal scale â¼10 µm) are successfully exfoliated into 0.5-4 nm (1-10 layers) thick h-BNNS with the same horizontal scale. Dynamic laser scattering and atomic force microscope data show that the yield is 47.6% (for the portion with the thickness of 0.5-6 nm), and all of the vertical sizes are reduced to smaller than 18 nm (45 layers).
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Development of bifunctional non-metal electrocatalyst for oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) with high efficiency, durable stability and low cost is a crucial and challenging issue. However, the heteroatom-doped carbon material including a carbon-based conductive additive would be easily oxidized under the high potential needed for driving the OER. Besides, the interaction between the heteroatom-doped carbon material that possesses electrocatalyst activity and a carbon-based conductive additive is weak, affecting the performance of the electrocatalyst. In this context, we introduce CoS nanoparticles into a three-dimensional N-doped carbon framework (CoS/NCF) by a morphology-retaining pyrolysis of polyaniline/CoS framework precursor, in which the polyaniline framework provides abundant functional groups to nucleate and grow CoS nanoparticles while retaining its interconnected three-dimensional porous structure. Benefiting from (i) the lower OER potential of CoS nanoparticles than the electro-oxidation decomposition potential of a carbon material and (ii) the strong affinity of CoS nanoparticles for a N-doped carbon framework, higher stability than commercial Pt/C system and greater catalytic activity towards ORR with an onset potential of about 0.921 V versus reversible hydrogen electrode (RHE) are observed. Furthermore, only a potential of 1.515 V versus RHE is required for achieving a current density of 10 mA cm-2.
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Development of two-way shape memory polymers that operate free of external force remains a great challenge. Here, the design criteria for this type of material are proposed, deriving a novel fabrication strategy accordingly, which employs conventional crosslinked polyurethane (PU) containing crystalline poly(ε-caprolactone) (PCL) as the proof-of-concept material. Having been simply trained by stretching and thermal treatment without additional ingredients and chemicals, the PU is coupled with a two-way shape memory effect. The core advancement of this study lies in the successful conversion of the inherent hydrogen bond network, which is often the easiest to overlook, into an internal stress provider. The temperature-dependent reversible melting/recrystallization of the crystalline phases elaborately works with the tensed hydrogen bond network, leading to implementation of the two-way shape memory effect. An average reversible strain of as high as ≈20% along the stretch direction is obtained through cooperation adjustment of chemical crosslinking density, crystallinity, and concentration of hydrogen bonds. Meanwhile, the highest internal tension offered by the hydrogen bond network is determined to be 0.10 MPa. Owing to the great convenience characterized by material selection, preparation, programming, and application, the current work may open up an avenue for production and usage of the smart material.
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Materiais Biocompatíveis/química , Poliésteres/química , Polímeros/química , Poliuretanos/química , Materiais Biocompatíveis/síntese química , Cristalização , Ligação de Hidrogênio , Estrutura Molecular , Polímeros/síntese química , Espectroscopia de Infravermelho com Transformada de Fourier , TemperaturaRESUMO
The present communication reports a novel strategy to fabricate reversible shape-memory polymer that operates without the aid of external force on the basis of a two-phase structure design. The proof-of-concept material, crosslinked styrene-butadiene-styrene block copolymer (SBS, dispersed phase)/polycaprolactone-based polyurethane (PU, continuous phase) blend, possesses a closely connected microphase separation structure. That is, SBS phases are chemically bonded to crosslinked PU by means of a single crosslinking agent and two-step crosslinking process for increasing integrity of the system. Miscibility between components in the blend is no longer critical by taking advantage of the reactive blending technique. It is found that a suitable programming leads to compressed SBS, which serves as internal expansion stress provider as a result. The desired two-way shape-memory effect is realized by the joint action of the temperature-induced reversible opposite directional deformabilities of the crystalline phase of PU and compressed SBS, accompanying melting and orientated recrystallization of the former. Owing to the broadness of material selection and manufacturing convenience, the proposed approach opens an avenue toward mass production and application of the smart polymer.
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Técnicas de Química Analítica , Polímeros/síntese química , Elastômeros , Fenômenos Mecânicos , Poliuretanos/química , Estirenos/química , TemperaturaRESUMO
A simple, effective and green bottom-up method for the synthesis of highly fluorescent N doped graphene oxide quantum dots (GOQDs) and polymer-like quantum dots (PQDs) was developed on the basis of rapid one-step microwave assisted pyrolysis of citric acid (CA) and diethylenetriamine (DETA) in different reaction solvents. Both one-photon-induced and two-photon-induced photoluminescence (PL) properties of the resultant GOQDs and PQDs were characterized and analyzed. The one-photon-induced PL quantum yields (QY) of GOQDs and PQDs reached 39.8 and 74.0%, respectively, which are high enough to exhibit strong photoluminescence (PL) emission even under daylight excitation. The origin of the PL behavior and PL quenching mechanism was explored in terms of the interaction between the functional groups on the surfaces of GOQDs or PQDs and Hg(2+). Furthermore, due to the excellent selectivity and sensitivity of the GOQDs and PQDs to Hg(2+), the quantum dots might be used for quantitative detection of Hg(2+) in aqueous solution.
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The present communication reports a concept battery made by direct contact of magnesium foil with ultralight polyaniline (PANI) foam in the absence of additional electrolyte. Electrical current is allowed to be steadily released from the junction with a specific energy of 646â mWh g(-1) and specific capacity of 1247â mAh g(-1). Additionally, the battery offers an environmentally friendly route of hydrogen production along with discharging. Mechanistic studies indicated that the ubiquitous galvanic corrosion combined with decomposition of adsorbed trace water in the semi-conducting polymer foam enabled the generation of electricity, which overturns the traditional view. The higher moisture level is conducive to the discharge. This work is believed to open up new possibilities for the design of electrochemical batteries.
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By using epoxy silane as a modifier and stabilizer, ZnO quantum dots (QDs) were synthesized by a one-step precipitation approach. The ZnO QDs acquired showed satisfactory redispersibility and exhibited strong and stable photoluminescence in both solution and dry states. When the ZnO QDs content was as high as 8 wt%, the ZnO QDs-epoxy nanocomposite was still highly transparent and luminescent. Accordingly, the ZnO QDs can be used as a luminescent material, and a cool white light emitting diode (WLED) lamp was made by encapsulating a UV chip with the nanocomposite, without traditional tricolor rare earth phosphors. Additionally, the high loading nanocomposite possessed high ultraviolet resistance, which would help to improve the lifetime of the WLED.
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Imparting excellent electrical properties, mechanical robustness, suppleness, conduction stability during deformation, and self-healing to intrinsic conducting polymers is a challenging endeavor. The reversibly interlocked macromolecular networks (RILNs) approach is utilized to tackle this problem. Specifically, poly(3,4-ethylenedioxythiophene) (PEDOT) is mixed with flexible polysulfonic acid networks crosslinked by reversible Diels-Alder bonds, while rigid polyaniline networks crosslinked by reversible Schiff base bonds act as molecular staples. Owing to the joint actions of the doping effect of polyaniline on PEDOT, the specific interlocking architecture and synergy between the component materials, the electrical conductivity (59.3-980.5 S cm-1), tensile strength (8.4-81.6 MPa) and elongation at break (44.5-411.0%) of the resultant PEDOT/RILNs films is significantly tunable according to different usage scenarios by adjusting the PEDOT content from 1.48 to 22.24 wt%. More importantly, the electrical resistance of PEDOT/RILNs remains constant during not only a single large extension and deflection but also repeated stretching (up to 1500 cycles) and bending (up to 106 cycles). The built-in reversible covalent bonds enable the PEDOT/RILNs to autonomously restore damaged mechanical and electrical performance. These record-breaking results and the demonstration of self-powered sensor made of PEDOT/RILNs suggest that the proposed approach successfully satisfies various conflicting requirements of flexible electronics regarding the properties of conducting polymers.
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Interconnecting macromolecules via multiple hydrogen bonds (H-bonds) can simultaneously strengthen and toughen polymers, but material synthesis becomes extremely difficult with increasing number of H-bonding donors and acceptors; therefore, most reports are limited to triple and quadruple H-bonds. Herein, this bottleneck is overcome by adopting a quartet-wise approach of constructing H-bonds instead of the traditional pairwise method. Thus, large multiple hydrogen bonds can be easily established, and the supramolecular interactions are further reinforced. Especially, when such multiple H-bond motifs are embedded in polymers, four macromolecular chains-rather than two as usual-are tied, distributing the applied stress over a larger volume and more significantly improving the overall mechanical properties. Proof-of-concept studies indicate that the proposed intermolecular multiple H-bonds (up to duodecuple) are readily introduced in polyurethane. A record-high tensile strength (105.2 MPa) is achieved alongside outstanding toughness (352.1 MJ m-3), fracture energy (480.7 kJ m-2), and fatigue threshold (2978.4 J m-2). Meantime, the polyurethane has acquired excellent self-healability and recyclability. This strategy is also applicable to nonpolar polymers, such as polydimethylsiloxane, whose strength (15.3 MPa) and toughness (50.3 MJ m-3) are among the highest reported to date for silicones. This new technique has good expandability and can be used to develop even more and stronger polymers.
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Ceramic-polymer composite solid electrolytes (CSEs) have attracted great attention by combining the advantages of polymer electrolytes and inorganic ceramic electrolytes. Herein, Li10GeP2S12 (LGPS) particles are incorporated into poly(ethylene oxide) (PEO)-based reversibly interlocked polymer networks (RILNs) derived from the topological rearrangement of two PEO networks cross-linked by reversible imine bonds and disulfide linkages. A series of highly ionic conductive, self-healing CSEs are obtained accordingly. The interlocking architecture successfully inhibits PEO crystallization, increasing the amorphous phase for Li ion transportation, and stabilizes the conductive pathways of LGPS particles by its unique confinement effect. Meanwhile, the LGPS particles cooperate with the RILN matrix, forming a filler-polymer interfacial phase for additional Li ion transportation and strengthening and toughening the resultant CSEs via the strong intermolecular Li+-O2- interactions. Furthermore, the dynamic characteristics of the included reversible bonds ensure a multiple intrinsic self-healing capability. Consequently, the CSEs containing 15 wt % LGPS deliver a high ionic conductivity (1.06 × 10-3 S cm-1) and high Li ion transference number (â¼0.6) at 25 °C, a wide electrochemical stability window (>4.9 V), good mechanical properties (0.63 MPa, 377%), and a stable CSE/Li anode interface. The integrated Li/CSE/LiFePO4 battery exhibits a specific discharge capacity of 110.8 mAh g-1 at 1 C (25 °C) and a capacity retention of 76.9% after 200 cycles. Thanks to the healability, the damaged CSEs can regain the structural integrity, ion conductive capability, and cycling performance of the assembled cells. The present work provides an effective strategy to fabricate CSEs for lithium metal batteries that are workable at ambient temperature.
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The development of photochemical self-healing polymers faces the the following bottlenecks: i) only the surface cracks can be restored and ii) materials' mechanical properties are lower. To break these bottlenecks, cross-linked poly(urethane-dithiocarbamate)s carrying photo-reversible dithiocarbamate bonds covalently linked to indole chromophores and benzyl groups are designed. The conjugated structure of the chromophore and benzyl enhances the addition reactivity of thiocarbonyl moiety and facilitates photo-cleavage of CS bond, so that transfer of the created radicals among dithiocarbamate linkages is promoted. Accordingly, reshuffling of the reversibly cross-linked networks via dynamic exchange between the activated dithiocarbamates is enabled in both surface layer and the interior upon exposure to the low-intensity ultraviolet (UV) light from the sun. It is found that the damages up to a centimeter below the surface can be effectively recovered in the sunshine, which greatly exceeds the maximum penetration distance of UV light (hundreds of microns). Besides, tensile strength and failure strain of the poly(urethane-dithiocarbamate) are superior to the reported photo-reversible polymers, achieving the record-high 33.8 MPa and 782.0% owing to the wide selectivity of soft/hard blocks, multiple interactions, and appropriate cross-linking architecture. The present work provides a novel paradigm of photo self-healing polymers capable of re-bonding cracks even out of the reach of the illumination.
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Simultaneously gluing hydrophobic and hydrophilic materials is a highly desired but intractable task. Herein, we developed a facile strategy using reversibly interlocked macromolecular networks (ILNs) as an adhesive. As shown by the proof-of-concept assembly of glass/ILNs/fluoropolymer (i.e., a simplified version of a photovoltaic module), the sandwiched ILNs were stratified after hot-pressing owing to temporary decrosslinking enabled by the built-in reversible covalent bonds. The fragmented component networks were enriched near their respective thermodynamically favored substrates to form a Janus-like structure. Strong elaborate interfacial bespoke chemical bonds and mechanical interlocking were thus established accompanied by the reconstruction of ILNs after cooling, which cooperated with the robust cohesion of the core part of the ILNs resulting from topological entanglements and led to a record-high peeling strength of 64.86 N cm-1. Also, the ILN-based Janus-like adhesive possessed reversible recyclability, adhesivity and on-demand de-bondability. The molecular design detailed in this study serves as a guide for developing a high-performance smart adhesive that firmly bonds non-sticking materials. Compared with existing Janus adhesives, our ILNs-based adhesive not only shows extremely useful reversibility but also greatly simplifies the adhesion process with no surface treatment required.
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To impart self-healing polymers largely adjustable dynamicity and mechanical performance, here we develop libraries of catalyst-free reversible polythioureas directly from commodity 1,4-phenylene diisothiocyanate and amines via facile click chemistry based modular assembly. By using the amine modules with various steric hindrances and flexibilities, the reversible thiourea units acquire triggering temperatures from room temperature to 120 °C. Accordingly, the derived self-healable, recyclable and controlled degradable dynamically crosslinked polythioureas can take effect within wide temperature range. Moreover, mechanical properties of the materials can be tuned covering plastics, elastomers and fibers using (i) different assemble modules or (ii) solid-state stretching. Particularly, unidirectional stretching leads to the record-high tensile strength of 266 MPa, while bidirectional stretching provides the materials with biaxial strengths up to over 120 MPa. The molecular mechanism and technological innovations discussed in this work may benefit promotion and application of self-healing polymers towards greatly diverse demands and scenarios.
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The colossal volumetric expansion (up to 300%) of the silicon (Si) anode during repeated charge-discharge cycles destabilizes the electrode structure and causes a drastic drop in capacity. Here in this work, commercial poly(acrylic acid) (PAA) is cross-linked by hydroxypropyl polyrotaxane (HPR) via reversible boronic ester bonds to achieve a water-soluble polymeric binder (PAA-B-HPR) for making the Si anode of the Li-ion battery. Slidable α-cyclodextrins of modified polyrotaxane are allowed to move around when the unwanted volume variation occurs in the course of lithiation and delithiation so that the accumulated internal stress can be equalized throughout the system, while the reversible boronic ester bonds are capable of healing the damages created during manufacturing and service to maintain the electrode integrity. As a result, the Li-ion battery assembled with the Si anode comprised of the PAA-B-HPR binder possesses outstanding specific capacity and cycle stability within a wide temperature range from 25 to 55 °C. Especially, the Si@PAA-B-HPR anode exhibits a discharge specific capacity of 1056 mA h/g at 1.4 A/g after 500 cycles under a higher temperature of 55 °C, and the corresponding capacity fading rate per cycle is only 0.10%. The present work opens an avenue toward the practical application of the Si anode for Li-ion batteries.
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ß-1,3-D-glucan has been reported to have a series of bioactivities including antitumor, antimicrobial, anti-inflammatory and antioxidative effects; however, its insolubility in neutral aqueous solution significantly restricts the potential application in biological and medicine fields. Herein, a water-soluble aminated ß-1,3-D-glucan (AG) was synthesized and the anti-inflammatory effect, cytotoxicity and plasmid DNA (pDNA) binding capacity of AG, serum stability, the particle sizes and zeta potentials of AG/pDNA nanocomposites, and the transfection efficiency and mechanism of action were studied. AG shows no obvious cytotoxicity within the range of working concentration (1-64 µg/ml) and it exerts potent anti-inflammatory effect independent on Dectin-1 and TLR2. AG/pDNA nanocomposites prepared by electrostatic interaction possess an appropriate particle size ranged from 192.8 to 118.4 nm and zeta potentials ranged from 20.880 to 27.16 mV with the N/P ratios from 5 to 100. AG/pDNA nanocomposites at the N/P ratios of 10 and 20 were able to show superior transfection efficiencies in RAW 264.7 cells as a result of their suitable particle size, zeta potential, anti-inflammatory effect, and the specific interaction with pattern recognition receptors (Dectin-1 and TLR2). These results indicate that AG is a potential candidate for DNA delivery system due to its potent anti-inflammatory effect and high transfection efficiency.
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Anti-Inflamatórios/farmacologia , Portadores de Fármacos , Terapia Genética/métodos , Proteoglicanas/química , Proteoglicanas/farmacologia , Transfecção/métodos , Animais , Sobrevivência Celular/efeitos dos fármacos , DNA/metabolismo , Técnicas de Transferência de Genes , Lectinas Tipo C/metabolismo , Camundongos , Nanocompostos , Tamanho da Partícula , Plasmídeos/genética , Proteoglicanas/toxicidade , Células RAW 264.7 , Receptor 2 Toll-Like/metabolismoRESUMO
Vinyl-functionalized periodic mesoporous organosilica materials (PMOs) with a crystal-like wall structure were synthesized, for the first time, by direct co-condensation of 1,4-bis(triethoxysilyl)benzene (BTEB) and triethoxyvinylsilane (TEVS). The synthesis approach led to high loading of vinyl functional groups and controlled regular morphologies. The resultant materials with different TEVS contents (up to 60 molar percentage) consisted of well-ordered mesopores (2.82-3.29 nm) with molecular-scale periodicity (7.6 A) in the walls, so that the high thermal stability of phenylene-bridged organosilica and versatile functionality of vinyl groups are combined. By exploring the influence of TEVS loading and the second monomer, tetraethoxysilane (TEOS), on the molecular-scale regularities, the rule of synergetic assembling of functional monosilylated TEVS and bissilylated BTEB was revealed. That is, the PMOs framework was built up only by BTEB, while TEVS was always terminally bonded to the channels surface.
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A novel strategy for developing homogeneous reversibly interlocking polymer networks (RILNs) with enhanced mechanical properties and underwater self-healing ability is proposed. The RILNs are prepared by the topological reorganization of two preformed cross-linked polymers containing reversible catechol-Fe3+ coordinate bonds and imine bonds and exhibit enhanced mechanical properties, superior underwater self-healing effect within a wide pH range, and water-assisted recycling ability through synergetic action between the reversible catechol-Fe3+ and imine bonds. At higher pH values, the catechol-Fe3+ coordinate bonds are responsible for self-healing, while the imine bonds maintain the stability of the materials. In neutral water, the imine bonds mainly account for self-healing, and hydrogen bonds and entanglements between the two networks prevent the material from collapsing. Under a lower pH value, intermolecular hydrogen bonds and entanglements contribute to self-healing. The outcomes of this work provide a new idea for developing robust multifunctional underwater self-healing materials.
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Implantable and wearable materials, which are usually used in/on a biological body, are mostly needed with biomimetic self-healing function. To enable repeatable large-wound self-healing and volume/structure recovery, we verified a proof-of-concept approach in this work. We design a polymer hydrogel that combines temperature responsiveness with an intrinsic self-healing ability through host-guest orthogonal self-assembly between two types of poly(N-isopropylacrylamide) (PNIPAM) oligomers. The result is thermosensitive, capable of fast self-repair of microcracks based on reversible host-guest assembly. More importantly, when a large open wound appears, the hydrogel can first close the wound via volume swelling and then completely self-repair the damage in terms of intrinsic self-healing. Meanwhile, its original volume can be easily recovered by subsequent contraction. As demonstrated by the experimental data, such millimeter-level wound self-healing and volume recovery can be repeatedly carried out in response to the short-term cooling stimulus. With low cytotoxicity and good biocompatibility, moreover, this highly intelligent hydrogel is greatly promising for practical large-wound self-healing in wound dressing, electronic skins, wearable biosensors, and humanoid robotics, which can tolerate large-scale human motions.