Electrically weldable conductive elastomers.

Flexible and stretchable electronic devices are subject to failure because of vulnerable circuit interconnections. We develop a low-voltage (1.5 to 4.5 V) and rapid (as low as 5 s) electric welding strategy to integrate both rigid electronic components and soft sensors in flexible circuits under ambient conditions. This is achieved through the design of conductive elastomers composed of borate ester polymers and conductive fillers, which can be self-welded and generate welding effects to various materials including metals, hydrogels, and other conductive elastomers. The welding effect is generated through the electrochemical reaction-triggered exposure of interfacial adhesive promotors or the cleavage/reformation of dynamic bonds. Our strategy can ensure both mechanical compliance and conductivity at the circuit interfaces and easily produce welding strengths in the kilopascal to megapascal range. The as-designed conductive elastomers in combination with the electric welding technique provide a robust platform for constructing standalone flexible and stretchable electronic devices that are detachable and assemblable on demand.

A Molecular Coordination Strategy for Regulating the Interface of MoS2 Field Effect Transistors.

Chemically modifying monolayer two-dimensional transition metal dichalcogenides (TMDs) with organic molecules provides a wide range of possibilities to regulate the electronic and optoelectronic performance of both materials and devices. However, it remains challenging to chemically attach organic molecules to monolayer TMDs without damaging their crystal structures. Herein, we show that the Mo atoms of monolayer MoS2 (1L-MoS2) in defect states can coordinate with both catechol and 1,10-phenanthroline (Phen) groups, affording a facile route to chemically modifying 1L-MoS2. Through the design of two isomeric molecules (LA2 and LA5) comprising catechol and Phen groups, we show that attaching organic molecules to Mo atoms via coordinative bonds has no negative effect on the crystal structure of 1L-MoS2. Both theoretical calculation and experiment results indicate that the coordinative strategy is beneficial for (i) repairing sulfur vacancies and passivating defects; (ii) achieving a long-term and stable n-doping effect; and (iii) facilitating the electron transfer. Field effect transistors (FETs) based on the coordinatively modified 1L-MoS2 show high electron mobilities up to 120.3 cm2 V-1 s-1 with impressive current on/off ratios over 109. Our results indicate that coordinatively attaching catechol- or Phen-bearing molecules may be a general method for the nondestructive modification of TMDs.

Carboxymethylcellulose hydrogels with stable carbon quantum dots: Enabling dynamic fluorescence modulation, automatic erasure, and secure information encryption.

Inspired by "disappear after reading", a time-modulated encryption hydrogel was synthesized by carboxymethyl cellulose with carbon quantum dots. Carboxymethyl cellulose in this system stabilized carbon quantum dots, which ensured the whole hydrogel worked well. The encryption/decryption of information depended on pH adjustment, application of EDTA and Cr (VI). Furthermore, an in-depth analysis of the fluorescence change mechanism uncovered that fluorescence quenching was potentially influenced by internal filtering effects and static quenching, which involved the amino, carboxyl, and hydroxyl groups present within the hydrogel.

A Novel P/N/Si-Containing Vanillin-Based Compound for a Flame-Retardant, Tough Yet Strong Epoxy Thermoset.

It is still extremely challenging to endow epoxy resins (EPs) with excellent flame retardancy and high toughness. In this work, we propose a facile strategy of combining rigid-flexible groups, promoting groups and polar phosphorus groups with the vanillin compound, which implements a dual functional modification for EPs. With only 0.22% phosphorus loading, the modified EPs obtain a limiting oxygen index (LOI) value of 31.5% and reach V-0 grade in UL-94 vertical burning tests. Particularly, the introduction of P/N/Si-containing vanillin-based flame retardant (DPBSi) improves the mechanical properties of EPs, including toughness and strength. Compared with EPs, the storage modulus and impact strength of EP composites can increase by 61.1% and 240%, respectively. Therefore, this work introduces a novel molecular design strategy for constructing an epoxy system with high-efficiency fire safety and excellent mechanical properties, giving it immense potential for broadening the application fields of EPs.

LDH@Boronate Polymer Core-Shell Nanoparticles: Nanostructure Design for Synergistically Enhancing the Flame Retardancy of Epoxy Resin.

As a promising nanofiller, layered double hydroxides (LDHs) can advance the fire safety of epoxy resin (EP), but so far, due to the problems of dispersion and low efficiency, it has still been a challenge to incorporate the flame retardancy and mechanical properties of EP nanocomposites effectively under the circumstance of a low additive amount. In this work, we take LDHs as the template, via the adsorption of a catechol group and the condensation polymerization between catechol groups and phenylboric acid groups, to prepare a core-shell structured nanoparticle LDH@BP, which contains rich flame-retardant elements. EP/LDH@BP nanocomposites were prepared by introducing LDH@BP into EP. The experimental results indicate that, compared with the original LDH, LDH@BP disperses uniformly in the EP matrix, and the flame retardancy and mechanical properties of EP/LDH@BP are significantly improved. At a relatively low content (5 wt%), EP/LDH@BP reached the rating of V-0 in the UL-94 test, LOI was increased to 29.1%, and peak heat release rate (PHRR) was reduced by 35.9% in cone calorimeter tests, which effectively inhibited the release of heat and toxic smoke during the combustion process of EP. Simultaneously, the mechanical properties of EP/LDH@BP have been improved satisfactorily. The above results derive from the reasonable architectural design of organic-inorganic nano-hybrid flame retardants and provide a novel method for the construction of efficient and balanced EP nanocomposite system with LDHs.

A Novel Anderson-Type POMs-Based Hybrids Flame Retardant for Reducing Smoke Release and Toxicity of Epoxy Resins.

Smoke emission and smoke toxicity have drawn more attention to improving the fire safety of polymers. In this work, a polyoxometalates (POMs)-based hybrids flame retardant (P-AlMo6 ) epoxy resin (EP) is prepared with toxicity-reduction and smoke-suppression properties via a peptide coupling reaction between POMs and organic molecules with double DOPO (bisDOPA). It combines the good compatibility of the organic molecule and the superior catalytic performance of POMs. Compared to pure EP, the glass transition temperature and flexural modulus of EP composite with 5 wt.% P-AlMo6 (EP/P-AlMo6 -5) are raised by 12.3 °C and 57.75%, respectively. Notably, at low flame-retardant addition, the average CO to CO2 ratio (Av-COY/Av-CO2 Y) is reduced by 33.75%. Total heat release (THR) and total smoke production (TSP) are lowered by 44.4% and 53.7%, respectively. The Limited Oxygen Index (LOI) value achieved 31.7% and obtained UL-94 V-0 rating. SEM, Raman, X-ray photoelectron spectroscopy, and TG-FTIR are applied to analyze the flame-retardant mechanism in condensed and gas phase. Outstanding flame retardant, low smoke toxicity properties are attained due to the catalytic carbonization ability of metal oxides Al2 O3 and MoO3 produced from the breakdown of POMs. This work advances the development of POMs-based hybrids flame retardants with low smoke toxicity properties.

Molecular Exchange of Dynamic Imine Bond for the Etching of Polymer Particles.

The underlying trend of colloidal synthesis has focused on extending the structure and composition complexity of colloidal particles. Hollow and yolk-shell particles are successful examples that have potential applications in frontier fields. In this paper, a facile and controllable etching method based on the molecular exchange of the dynamic imine bond to generate cavities in polymer particles is developed. Starting from boronate ester polymer particles and inorganic@boronate core-shell particles with the imine bonds incorporated in the polymer networks, the etching method easily affords hollow and yolk-shell particles with tunable shell thicknesses. The molecular exchange dynamics analysis indicates that guest amine molecules cause the reconstruction of imine bonds and the leakage of molecular and oligomer fragments, resulting in the formation of the hollow structure. This molecular exchange-based etching method may be of interest in the construction of polymer architectures with increased composition and structure complexities.

In Situ Generation of Ultrathin MoS2 Nanosheets in Carbon Matrix for High Energy Density Photo-Responsive Supercapacitors.

Stimuli-responsive supercapacitors have attracted broad interest in constructing self-powered smart devices. However, due to the demand for high cyclic stability, supercapacitors usually utilize stable or inert electrode materials, which are difficult to exhibit dynamic or stimuli-responsive behavior. Herein, this issue is addressed by designing a MoS2 @carbon core-shell structure with ultrathin MoS2 nanosheets incorporated in the carbon matrix. In the three-electrode system, MoS2 @carbon delivers a specific capacitance of 1302 F g-1 at a current density of 1.0 A g-1 and shows a 90% capacitance retention after 10 000 charging-discharging cycles. The MoS2 @carbon-based asymmetric supercapacitor displays an energy density of 75.1 Wh kg-1 at the power density of 900 W kg-1 . Because the photo-generated electrons can efficiently migrate from MoS2 nanosheets to the carbon matrix, the assembled photo-responsive supercapacitor can answer the stimulation of ultraviolet-visible-near infrared illumination by increasing the capacitance. Particularly, under the stimulation of UV light (365 nm, 0.08 W cm-2 ), the device exhibits a ≈4.50% (≈13.9 F g-1 ) increase in capacitance after each charging-discharging cycle. The study provides a guideline for designing multi-functional supercapacitors that serve as both the energy supplier and the photo-detector.

Metallopolymer Particle Engineering via Etching of Boronate Polymers toward High-Performance Overall Water Splitting Catalysts.

Metallopolymers combine the property features of both metallic compounds and organic polymers, representing a typical direction for the design of high-performance hybrid materials. Here, a highly adaptive etching method to create pores and cavities in the metallopolymer particles is established. Starting from boronate polymer (BP) and inorganic@BP core-shell particles, porous, hollow, and yolk-shell metallopolymer particles can be fabricated, respectively. By taking advantage of the easy control over composition and pore/cavity structure, these metallopolymer particles provide a universal platform for the fabrication of nitrogen, boron co-doped carbon nanocomposites loaded with metals (M-NBCs). The as-prepared M-NBCs exhibit remarkable catalytic activities toward oxygen evolution reaction and hydrogen evolution reaction. An alkaline overall water splitting cell assembled by using M-NBCs as the anode and cathode can be driven by a single AAA battery. The proposed strategy for the construction of metallopolymer composites may enlighten for the design of complex hybrid nanomaterials.

Self-activatable carbon nanotube@ruthenium-catechol coordination complex for hydrogen evolution reaction.

We report a simple metal ion-catechol coordination strategy to coat ruthenium-catechol polymer complex (TAC-Ru) on the surface of carbon nanotubes (CNT) to form a core-shell structure (abbreviated as CNT@TAC-Ru). This is achieved by firstly polymerizing catechol and boronic acid monomers on the surface of CNT to form a boronate ester polymer (BP) shell. Then, Ru3+is used to etch the BP shell, and cleave the dynamic boronate ester bond, leading to the formation of a CNT@ruthenium-catechol coordination complex based on the coordinative efficiency of the catechol group. The electrocatalytic property of the CNT@TAC-Ru composite can be activated through electrochemical cycling treatment. The as-activated CNT@TAC-Ru exhibits evidently improved hydrogen evolution reaction (HER) performance with an overpotential of 10 mV in 1.0 M KOH at a current density of 10 mA cm-2, which is better than that of commercial Pt/C (32 mV). And the long-term stability is also desirable. This work provides a pyrolysis-free method to form metal-polymer-carbon composite with high HER performance under the alkaline condition.

Diblock Copolymers Containing Titanium-Hybridized Polyhedral Oligomeric Silsesquioxane Used as a Macromolecular Flame Retardant for Epoxy Resin.

In this paper, the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-containing diblock copolymer poly[(p-hydroxybenzaldehyde methacrylate)m-b-(2-((6-oxidodibenzo[c,e][1,2]oxaphosphinin-6-yl)oxy)ethyl methacrylate)n] (abbrev. poly(HAMAm-b-HEPOMAn)) was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. When it was continued to react with titanium-hybridized aminopropyl-polyhedral oligomeric silsesquioxane (Ti-POSS) through a Schiff-base reaction, new grafted copolymers poly[(Ti-POSS-HAMA)m-b-HEPOMAn] (abbrev. PolyTi) were obtained. Then, they were used as macromolecular flame retardant to modify epoxy resin materials. The thermal, flame retardant and mechanical properties of the prepared EP/PolyTi composites were tested by TGA, DSC, LOI, UL-94, SEM, Raman, DMA, etc. The migration of phosphorus moiety from epoxy resin composites was analyzed by immersing the composites into ethanol/H2O solution and recording the extraction solution by UV-Vis spectroscopy. The results showed that the added PolyTi enhanced the glass transition temperature, the carbon residue, the graphitization of char, LOI, and mechanical properties of the EP/PolyTi composites when compared to pure cured EP. Furthermore, the phosphorus moieties were more likely to migrate from EP/DOPO composites than that from EP/PolyTi composites. Obviously, compared with small molecular flame retardant modified EP, the macromolecular flame retardant modified EP/PolyTi composites exhibited better thermal stability, flame retardancy, and resistance to migration.

Asymmetric Hydrophosphonylation of Imines to Construct Highly Stable Covalent Organic Frameworks with Efficient Intrinsic Proton Conductivity.

Imine-linked covalent organic frameworks (COFs) have received widespread attention because of their structure features such as high crystallinity and tunable pores. However, the intrinsic reversibility of the imine bond leads to the poor stability of imine-linked COFs under strong acid conditions. Also, their thermal stability is significantly lower than that of many other COFs. Herein, we report for the first time that the reversible imine bonds in the skeleton of COFs can be locked through the asymmetric hydrophosphonylation reaction of phosphite. The functionalized COFs not only retain the crystallinity and porous structure but also exhibit evidently improved chemical and thermal stabilities. In addition, the phosphorous acid groups generated by acidic hydrolysis attached to the skeleton endow the COFs with good intrinsic proton conductivity. Due to the diversity of phosphite derivatives and imine-linked COFs, this work may provide an avenue for extending the COF structures and functions through the asymmetric hydrophosphonylation reaction.

Three-Dimensional hybrid structure loader type flexible supercapacitor based on Polyvinyl alcohol gel and Acetylene black.

In order to overcome the structural drawbacks of layered electrodes in flexible supercapacitors, the construction of an electrode frame with high adaptability for the loading of different active materials makes the production of flexible supercapacitors simpler and more accurate. Herein, a novel loader type flexible supercapacitor with three-dimensional hybrid structure is built. In our design, the acetylene black and active material are enriched in the polyvinyl alcohol matrix, and the three-dimensional conductive network that can load different active material is formed. The active material can be selected on demand. The basic electrode (also a loader) formed by polyvinyl alcohol and acetylene black is an electronic conductor (∼1 Scm-1) with good electrochemical and mechanical performance. By loading active materials in this basic electrode, more powerful flexible electrodes can be built easily and accurately with the same steps according to the designed proportion. Electrodes constructed according to this method deliver nonnegligible surface capacity (e.g. 1.1 Fcm-2 in surface capacitance, polyaniline/carbon nanotube composite as active materials) with good response, rate performance, excellent durability (10000 times of charge-discharge), and good foldability (1000 times of folding). This pattern of carrier type electrodes provides a simple and universal strategy for manufacturing flexible supercapacitors.

K+-Responsive Crown Ether-Based Amphiphilic Copolymer: Synthesis and Application in the Release of Drugs and Au Nanoparticles.

Due to unique chelating and macrocyclic effects, crown ether compounds exhibit wide application prospects. They could be introduced into amphiphilic copolymers to provide new trigger mode for drug delivery. In this work, new amphiphilic random polymers of poly(lipoic acid-methacrylate-co-poly(ethylene glycol) methyl ether methacrylate-co-N-isopropylacrylamide-co-benzo-18-crown-6-methacrylamide (abbrev. PLENB) containing a crown ether ring and disulphide bond were synthesized via RAFT polymerization. Using the solvent evaporation method, the PLENB micelles were formed and then used to load substances, such as doxorubicin hydrochloride (DOX) and gold nanoparticles. The results showed that PLENB exhibited a variety of lowest critical solution temperature (LCST) in response to the presence of different ions, such as K+, Na+ and Mg2+. In particular, the addition of 150 mM K+ increased the LCST of PLENB from 31 to 37 °C and induced the release of DOX from the PLENB@DOX assemblies with a release rate of 99.84% within 12 h under 37 °C. However, Na+ and Mg2+ ions could not initiate the same response. Furthermore, K+ ions drove the disassembly of gold aggregates from the PLENB-SH@Au assemblies to achieve the transport of Au NPs, which is helpful to construct a K+-triggered carrier system.

Electrically programmable adhesive hydrogels for climbing robots.

Although there have been notable advances in adhesive materials, the ability to program attaching and detaching behavior in these materials remains a challenge. Here, we report a borate ester polymer hydrogel that can rapidly switch between adhesive and nonadhesive states in response to a mild electrical stimulus (voltages between 3.0 and 4.5 V). This behavior is achieved by controlling the exposure and shielding of the catechol group through water electrolysis-induced reversible cleavage and reformation of the borate ester moiety. By switching the electric field direction, the hydrogel can repeatedly attach to and detach from various surfaces with a response time as low as 1 s. This programmable attaching/detaching strategy provides an alternative approach for robot climbing. The hydrogel is simply pasted onto the moving parts of climbing robots without complicated engineering and morphological designs. Using our hydrogel as feet and wheels, the tethered walking robots and wheeled robots can climb on both vertical and inverted conductive substrates (i.e., moving upside down) such as stainless steel and copper. Our study establishes an effective route for the design of smart polymer adhesives that are applicable in intelligent devices and an electrochemical strategy to regulate the adhesion.

Kinetics control over the Schiff base formation reaction for fabrication of hierarchical porous carbon materials with tunable morphology for high-performance supercapacitors.

Schiff base formation reaction is highly dynamic, and the microstructure of Schiff base polymers is greatly affected by reaction kinetics. Herein, a series of Schiff base cross-linked polymers (SPs) with different morphologies are synthesized through adjusting the species and amount of catalysts. Nitrogen/oxygen co-doped hierarchical porous carbon nanoparticles (HPCNs), with tunable morphology, specific surface area (SSA) and porosity, are obtained after one-step carbonization. The optimal sample (HPCN-3) possesses a coral reef-like microstructure, high SSA up to 1003 m2g-1, and a hierarchical porous structure, exhibiting a remarkable specific capacitance of 359.5 F g-1(at 0.5 A g-1), outstanding rate capability and cycle stability in a 1 M H2SO4electrolyte. Additionally, the normalized electric double layer capacitance (EDLC) and faradaic capacitance of HPCN-3 are 0.239 F m-2and 10.24 F g-1respectively, certifying its superior electrochemical performance deriving from coral reef-like structure, high external surface area and efficient utilization of heteroatoms. The semi-solid-state symmetrical supercapacitor based on HPCN-3 delivers a capacitance of 55 F g-1at 0.5 A g-1, good cycle stability of 86.7% after 5000 GCD cycles at 10 A g-1, and the energy density ranges from 7.64 to 4.86 Wh kg-1.

Characterizing the Brownian Diffusion of Nanocolloids and Molecular Solutions: Diffusion-Ordered NMR Spectroscopy vs Dynamic Light Scattering.

Hydrodynamic size is a characteristic dimension that reflects the Brownian diffusion of objects, such as proteins, macromolecules, and various colloids when dissolved/dispersed in fluid phases. This property is crucial when investigating the utility of colloidal nanocrystals and polymeric materials in biology. Dynamic light scattering (DLS) has been widely used to measure the diffusion coefficient and hydrodynamic size of such systems. Comparatively, diffusion-ordered NMR spectroscopy (DOSY-NMR) is a relatively new analytical method that has provided researchers with an alternative experimental approach to access such information. Here, we apply DLS and DOSY-NMR simultaneously to characterize the diffusion coefficient and hydrodynamic size of several sets of nanocolloids, including dispersions of gold nanoparticles and luminescent quantum dots that are surface-capped with either hydrophobic or hydrophilic coatings, as well as a monomer and a low-molecular-weight polymer. We compare, side by side, the findings acquired from each measurement, which has allowed us to identify the benefits and constraints of each technique. Our results show that the two approaches provide comparable data when larger size nanocolloids are probed. However, we find that DOSY is substantially more effective in characterizing nanocolloids that are fluorescent and/or have very small dimensions, as well as molecular-scale organic ligands, where DLS reaches its limit. Additionally, we find that, compared to DLS, DOSY tends to require higher solute concentrations and longer collection time to generate data with high signal-to-noise ratios.

Design of Slidable Polymer Networks: A Rational Strategy to Stretchable, Rapid Self-Healing Hydrogel Electrolytes for Flexible Supercapacitors.

Hydrogel electrolytes are of particular interest in the fabrication of flexible supercapacitors that are able to withstand deformation and physical damage. Nevertheless, there still exists a huge space in the design of hydrogel electrolytes with comprehensive performances including high processability, conductivity, mechanical strength, and self-healability. Herein, a slidable polymer network is constructed through the cross-linking reaction among commercially available polyethyleneimine (PEI), polyvinyl alcohol (PVA), and 4-formylphenylboronic acid (Bn) to generate PEI-PVA-Bn hydrogels, which have high adaptability to various electrolytes such as LiCl, NaCl, KCl, and ionic liquids. The as formed hydrogel electrolytes not only show excellent mechanical property (elongation at break up to 1223%, strength of 34.6 kPa) and self-healability (highest strain self-healing efficiency reaches 94.3% within 2 min) but also exhibit high conductivity (up to 21.49 mS cm-1). Flexible supercapacitors constructed by sandwiching the PEI-PVA-Bn-LiCl hydrogel electrolyte between two multiwalled carbon nanotube electrodes demonstrate a broadened operating potential window of 1.4 V, specific capacitance of 16.7 mF cm-2, high cycling stability up to 10 000 charge/discharge cycles, and excellent mechanical stability.

Superhydrophobic and flame retardant cotton modified with DOPO and fluorine-silicon-containing crosslinked polymer.

Modification of cotton fabric to achieve superhydrophobic, self-cleaning and heat resistance is of particular interest for practical applications. Herein, a simple surface modification route is designed to introduce flame retardant component 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and low surface energy crosslinked polymer network comprising both fluorine and silicon elements on the surface of cotton fabric. The modified cotton fabric shows characteristic of superhydrophobic property with water contact angle of 154.8°, and exhibits promising self-cleaning performance. With the characters of hydrophobicity and lipophilicity, the modified cotton fabric can efficiently separate oil-water mixture and even emulsion. Moreover, the introduction of DOPO and fluorine-silicon-containing coating not only enhances the heat resistance of cotton, but also improves the flame retardant property.

Predictable Particle Engineering: Programming the Energy Level, Carrier Generation, and Conductivity of Core-Shell Particles.

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.