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Artificial skin that simultaneously mimics sensory feedback and mechanical properties of natural skin holds substantial promise for next-generation robotic and medical devices. However, achieving such a biomimetic system that can seamlessly integrate with the human body remains a challenge. Through rational design and engineering of material properties, device structures, and system architectures, we realized a monolithic soft prosthetic electronic skin (e-skin). It is capable of multimodal perception, neuromorphic pulse-train signal generation, and closed-loop actuation. With a trilayer, high-permittivity elastomeric dielectric, we achieved a low subthreshold swing comparable to that of polycrystalline silicon transistors, a low operation voltage, low power consumption, and medium-scale circuit integration complexity for stretchable organic devices. Our e-skin mimics the biological sensorimotor loop, whereby a solid-state synaptic transistor elicits stronger actuation when a stimulus of increasing pressure is applied.

Flexible sensors based on ionogels show great potential in wearable devices because of their compliance and deformability.

'Smart' bandages based on multimodal wearable devices could enable real-time physiological monitoring and active intervention to promote healing of chronic wounds. However, there has been limited development in incorporation of both sensors and stimulators for the current smart bandage technologies. Additionally, while adhesive electrodes are essential for robust signal transduction, detachment of existing adhesive dressings can lead to secondary damage to delicate wound tissues without switchable adhesion. Here we overcome these issues by developing a flexible bioelectronic system consisting of wirelessly powered, closed-loop sensing and stimulation circuits with skin-interfacing hydrogel electrodes capable of on-demand adhesion and detachment. In mice, we demonstrate that our wound care system can continuously monitor skin impedance and temperature and deliver electrical stimulation in response to the wound environment. Across preclinical wound models, the treatment group healed ~25% more rapidly and with ~50% enhancement in dermal remodeling compared with control. Further, we observed activation of proregenerative genes in monocyte and macrophage cell populations, which may enhance tissue regeneration, neovascularization and dermal recovery.

Intrinsically stretchable bioelectronic devices based on soft and conducting organic materials have been regarded as the ideal interface for seamless and biocompatible integration with the human body. A remaining challenge is to combine high mechanical robustness with good electrical conduction, especially when patterned at small feature sizes. We develop a molecular engineering strategy based on a topological supramolecular network, which allows for the decoupling of competing effects from multiple molecular building blocks to meet complex requirements. We obtained simultaneously high conductivity and crack-onset strain in a physiological environment, with direct photopatternability down to the cellular scale. We further collected stable electromyography signals on soft and malleable octopus and performed localized neuromodulation down to single-nucleus precision for controlling organ-specific activities through the delicate brainstem.

An epoxy resin modified by coordination between Ni2+ and imidazole/hydroxyl groups show high mechanical strength and thermal healing/recycling/reprocessing/thermochromic behavior, and might be useful in the field of thermally-responsive smart windows.

Flower-like polyacrylonitrile (PAN) particles have shown promising performance for numerous applications, including sensors, catalysis, and energy storage. However, the detailed formation process of these unique structures during polymerization has not been investigated. Here, we elucidate the formation process of flower-like PAN particles through a series of in situ and ex situ experiments. We have the following key findings. First, lamellar petals within the flower-like particles were predominantly orthorhombic PAN crystals. Second, branching of the lamellae during the particle formation arose from PAN's fast nucleation and growth on pre-existing PAN crystals, which was driven by the poor solubility of PAN in the reaction solvent. Third, the particles were formed to maintain a constant center-to-center distance during the reaction. The separation distance was attributed to strong electrostatic repulsion, which resulted in the final particles' spherical shape and uniform size. Lastly, we employed the understanding of the formation mechanism to tune the PAN particles' morphology using several experimental parameters including incorporating comonomers, changing temperature, adding nucleation seeds, and adjusting the monomer concentration. These findings provide important insights into the bottom-up design of advanced nanostructured PAN-based materials and controlled polymer nanostructure self-assemblies.

Artificial skins reproducing properties of human skin are emerging and significant for study in various areas, such as robotics, medicine, and textiles. Perspiration, as one of the most imperative thermoregulation functions of human skin, is gaining increasing attention, but how to realize ideal artificial skin for perspiration simulation remains challenging. Here, an integrated 3D hydrophilicity/hydrophobicity design is proposed for artificial sweating skin (i-TRANS). Based on normal fibrous wicking materials, the selective surface modification with gradient of poly(dimethylsiloxane) (PDMS) creates hydrophilicity/hydrophobicity contrast in both lateral and vertical directions. With the additional help of bottom hydrophilic Nylon 6 nanofibers, the constructed i-TRANS is able to transport "sweat" directionally without trapping undesired excess water and attain uniform "secretion" of sweat droplets on the top surface, decently mimicking human skin perspiration situation. This fairly comparable simulation not only presents new insights for replicating skin properties, but also provides proper in vitro testing platforms for perspiration-relevant research, greatly avoiding unwanted interference from the "skin" layer. In addition, the facile, fast, and cost-effective fabrication approach and versatile usage of i-TRANS can further facilitate its application.

Intrinsically stretchable bioelectronic devices based on soft and conducting organic materials have been regarded as the ideal interface for seamless and biocompatible integration with the human body. However, the grand challenge remains for the conducting polymer to possess both high mechanical ductility and good electrical conduction at cellular level feature sizes. This longstanding material limitation in organic bioelectronics has impeded the full exploitation of its unique benefits. Here, we introduce a new molecular engineering strategy based on rationally designed topological supramolecular networks, which allows effective decoupling of competing effects from multiple molecular building blocks to meet complex requirements. We achieve two orders of magnitude improvement in the conductivity under 100% strain in physiological environment, along with the capability for direct photopatterning down to 2 μm. These unprecedented capabilities allow us to realize previously inaccessible bioelectronic applications including high-resolution monitoring of ‘soft and malleable’ creatures, e.g., octopus, and localized neuromodulation down to single nucleus precision for controlling organ-specific activities through delicate tissues, e.g., brainstem.

1,2-Dimethoxyethane (DME) is a common electrolyte solvent for lithium metal batteries. Various DME-based electrolyte designs have improved long-term cyclability of high-voltage full cells. However, insufficient Coulombic efficiency at the Li anode and poor high-voltage stability remain a challenge for DME electrolytes. Here, we report a molecular design principle that utilizes a steric hindrance effect to tune the solvation structures of Li+ ions. We hypothesized that by substituting the methoxy groups on DME with larger-sized ethoxy groups, the resulting 1,2-diethoxyethane (DEE) should have a weaker solvation ability and consequently more anion-rich inner solvation shells, both of which enhance interfacial stability at the cathode and anode. Experimental and computational evidence indicates such steric-effect-based design leads to an appreciable improvement in electrochemical stability of lithium bis(fluorosulfonyl)imide (LiFSI)/DEE electrolytes. Under stringent full-cell conditions of 4.8 mAh cm-2 NMC811, 50 μm thin Li, and high cutoff voltage at 4.4 V, 4 M LiFSI/DEE enabled 182 cycles until 80% capacity retention while 4 M LiFSI/DME only achieved 94 cycles. This work points out a promising path toward the molecular design of non-fluorinated ether-based electrolyte solvents for practical high-voltage Li metal batteries.

Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facile patternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C–H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V−1 s−1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics., Next-generation skin-inspired electronics require enhanced mechanical robustness and device complexity including elasticity, solvent resistance, and facile patternability. Here, the authors show a molecular design concept that simultaneously achieves all these requirements by covalently linking an in-situ formed rubber matrix with polymer electronic materials.

Next-generation light-emitting displays on skin should be soft, stretchable and bright

Strategies to improve stretchability of polymer semiconductors, such as introducing flexible conjugation-breakers or adding flexible blocks, usually result in degraded electrical properties. In this work, we propose a concept to address this limitation, by introducing conjugated rigid fused-rings with optimized bulky side groups and maintaining a conjugated polymer backbone. Specifically, we investigated two classes of rigid fused-ring systems, namely, benzene-substituted dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (Ph-DBTTT) and indacenodithiophene (IDT) systems, and identified molecules displaying optimized electrical and mechanical properties. In the IDT system, the polymer PIDT-3T-OC12-10% showed promising electrical and mechanical properties. In fully stretchable transistors, the polymer PIDT-3T-OC12-10% showed a mobility of 0.27 cm2 V-1 s-1 at 75% strain and maintained its mobility after being subjected to hundreds of stretching-releasing cycles at 25% strain. Our results underscore the intimate correlation between chemical structures, mechanical properties, and charge carrier mobility for polymer semiconductors. Our described molecular design approach will help to expedite the next generation of intrinsically stretchable high-performance polymer semiconductors.

Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to ∼1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers., We report an approach to achieve a high energy density shape memory polymer based on the formation of strain-induced supramolecular nanostructures, which immobilize stretched chains to store entropic energy.

Dielectric actuators are prone to be worn or partially damaged when operating at high electric fields. The introduction of self-healing features into dielectric actuators is favorable for extending its life span and security. Although many attempts have been made to produce self-healing dielectric actuators, most of them focus on the healing of either the electrodes or the dielectric layers. A dielectric actuator that exhibits integral self-healing is still unprecedented. Meanwhile, realizing integral self-healing in dielectric actuator is highly challenging because both the electrode and the dielectric layer need to be healed while the interface between the electrode and the dielectric layer should remain unaffected during the healing process. In this paper, we synthesized self-healing polydimethylsiloxane (PDMS) polymers containing different amounts of polyaniline (PANI) (denoted as PDMS-PANI

In order to understand the mechanical and self-healing properties of polymers cross-linked by Fe(III)-2,6-pyridinedicarboxamide (pdca) coordination complexes, herein we performed the reaction between 2,6-pyridinedicarboxamide and FeCl3 under both neutral and alkaline conditions, and studied the dynamic ligand exchange properties of the resulting model complexes. The results showed that [Fe(Hpdca)]+ exhibited a rapid ligand exchange property which was not observed for [Fe(pdca)]−. Correspondingly, polymer Fe-Hpdca-PBCA (PBCA = poly(butadiene-co-acrylonitrile)) was weak, highly stretchable and self-healable, while Fe-pdca-PBCA was strong and poorly stretchable and can only be partially healed with a prolonged time. These results deliver a clear indication of the important impact of the bond strength and dynamics of coordination complexes on the mechanical and self-healing properties of polymers. Such an understanding is helpful for further design of novel synthetic polymers which can achieve an optimal balance between the mechanical strength and self-healing performance.

Polymer-bonded explosives (PBXs) are often subjected to different external environmental conditions with various temperature and humidity during long-term storage, transportation, and usage process. The change in temperature and humidity will result in PBXs cracks formation and cause higher risk of explosion evolution when undergoing various stimulus including impact or friction. Herein, a self-healing polymer binder is developed to solve this problem. The fluoropolymer gel binder, a PVDF-co-HFP (copolymer of CH2-CF2 and CF2-CF(CF3))/EMIOTf (1-ethyl-3-methylimidazolium trifluoromethanesulfonate)/graphene ternary composite, has high density, high thermal conductivity, excellent interfacial adhesion property, and exhibits self-healing ability at room temperature. Highly filled PBXs composites with 95% of explosive 2, 6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105) and 5% of ternary composite are fabricated. The as-prepared PBX samples have high denotation parameter (7800 m s−1), low impact sensitivities (11–12 J), and low friction sensitivity (no sparks was observed even at friction energy load of 0.36 N). More importantly, our PBXs have effective crack healing ability within 48 h at room temperature. Therefore, the stability and safety of PBXs are improved through the self-healing polymer binder. Such PBXs can find widespread application in various military and civil fields.

Achieving a desirable combination of solid-like properties and fast self-healing is a great challenge due to slow diffusion dynamics. In this work, we describe a design concept that utilizes weak but abundant coordination bonds to achieve this objective. The designed PDMS polymer, crosslinked by abundant Zn(II)-carboxylate interactions, is very strong and rigid at room temperature. As the coordination equilibrium is sensitive to temperature, the mechanical strength of this polymer rapidly and reversibly changes upon heating or cooling. The soft–rigid switching ability σ, defined as G’max /G’min, can reach 8000 when ΔT = 100 °C. Based on these features, this polymer not only exhibits fast thermal-healing properties, but is also advantageous for various applications such as in orthopedic immobilization, conductive composites/adhesives, and 3D printing., Combining solid-like properties with fast self-healing is a great challenge due to slow diffusion dynamics. Here the authors demonstrate a rigid and healable material by using weak but abundant coordination bonds to crosslink a PDMS polymer.

Dual-functional polymeric system combining shape memory with self-healing properties has attracted increasingly interests of researchers, as both of these properties are intelligent and promising characteristics. Moreover, shape memory polymer that functions at human body temperature (37 &deg, C) are desirable because of their potential applications in biomedical field. Herein, we designed a polymer network with a permanent covalent crosslinking and abundant weak hydrogen bonds. The former introduces elasticity responsible and maintain the permanent shape, and the latter contributes to the temporary shape via network rearrangement. The obtained PDMS-COO-E polymer films exhibit excellent mechanical properties and the capability to efficiently self-heal for 6 h at room temperature. Furthermore, the samples turn from a viscous state into an elastic state at 37 &deg, C. Therefore, this polymer has shape memory effects triggered by body temperature. This unique material will have a wide range of applications in many fields, containing wearable electronics, biomedical devices, and 4D printing.

A stiff and healable polymer is obtained by using the dynamic-covalent boroxine bond to crosslink PDMS chain into 3D networks. The as-prepared polymer is very strong and stiff, and can bear a load of more than 450 times its weight. When damaged, it can be completely healed upon heating after wetting.

There is often a trade-off between mechanical properties (modulus and toughness) and dynamic self-healing. Here we report the design and synthesis of a polymer containing thermodynamically stable whilst kinetically labile coordination complex to address this conundrum. The Zn-Hbimcp (Hbimcp = 2,6-bis((imino)methyl)-4-chlorophenol) coordination bond used in this work has a relatively large association constant (2.2 × 1011) but also undergoes fast and reversible intra- and inter-molecular ligand exchange processes. The as-prepared Zn(Hbimcp)2-PDMS polymer is highly stretchable (up to 2400% strain) with a high toughness of 29.3 MJ m−3, and can autonomously self-heal at room temperature. Control experiments showed that the optimal combination of its bond strength and bond dynamics is responsible for the material’s mechanical toughness and self-healing property. This molecular design concept points out a promising direction for the preparation of self-healing polymers with excellent mechanical properties. We further show this type of polymer can be potentially used as energy absorbing material., There is often a trade-off between mechanical properties (modulus and toughness) and dynamic self-healing in materials. Here the authors design and synthesize a polymer containing thermodynamically stable whilst kinetically labile coordination complexes to address this conundrum.

This paper outlines theoretically investigations of the probability density distribution (PDD) of ranging data for the imaging laser radar (ILR) system operating at a wavelength of 905 nm under the fog condition. Based on the physical model of the reflected laser pulses from a standard Lambertian target, a theoretical approximate model of PDD of the ranging data is developed under different fog concentrations, which offer improved precision target ranging and imaging. An experimental test bed for the ILR system is developed and its performance is evaluated using a dedicated indoor atmospheric chamber under homogeneously controlled fog conditions. We show that the measured results are in good agreement with both the accurate and approximate models within a given margin of error of less than 1%.

By oxidation of a couple of chiral cyclometalated platinum(II) complexes, Pt(La)(CC–Ph) (1a) and Pt(Lb)(CC–Ph) (1b) (La = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine and Lb = (+)-4,5-pinene-6'-phenyl-2,2’-bipyridine), a novel pair of platinum(IV) enantiomers, Pt(La)(CC–Ph)3 (2a) and Pt(Lb)(CC–Ph)3 (2b), were obtained. According to the single crystal X-ray diffraction studies of 2a and 2b, the central platinum atom is wrapped by a C^N^N ligand and three phenylacetylene groups and exhibits a distorted octahedral geometry. Due to the different coordination configurations and electronic structures, complexes 2a and 2b are distinct from 1a and 1b not only in absorption and emission spectra, but also in their chiroptical properties. The oxidation reaction of 1a and 1b is a kinetically controllable process. Given different oxidants to complete the Pt(II)-to-Pt(IV) process, various oxidation rates were presented. The difference between the ECD spectra of complexes 1a and 2a has been confirmed through TD-DFT calculation and can be useful for designing new redox-responsive materials.

This paper presents a mechatronic system approach to the improvement of part straightness accuracy in rough cutting of wire electrical discharge machining (wire EDM). The mechatronic system design integrated an active wire feed apparatus and a microcontroller-based wire tension control system into a novel wire transport system for providing a smooth wire transport and a constant wire tension value. The active wire feed apparatus was first devised to reduce the inertial effect of the wire spool on the wire transport system. Then, a proportional-integral-derivative (PID) controller was used to implement real-time wire tension control of the wire transport system. Compared to a typical wire transport system, steady-state error of wire tension control can be reduced by half using the newly developed system. Through pulse train analysis, the proportion of normal sparks to total sparks defined as normal spark ratio can be used to monitor spark gap condition as well as to be an indication of evaluating machining speed and part straightness accuracy. Experimental results show that part straightness accuracy can be significantly improved from 13 to 4 μm by the newly developed wire transport system along with optimum machining settings.

In this paper, a prediction technique for the best coding unit (CU) partition tree is proposed to avoid the repeated computation on the variable-sized prediction units (PU) and transform units (TU) in high efficiency video coding (HEVC). In HEVC, many advanced coding tools are introduced to decrease the bit-rate of coded videos with higher visual quality. Of these tools, many seek to partition each CU in the incoming frame into a quad-tree structure of variable sized blocks while performing prediction and transform computations to obtain the optimal rate-distortion performance. During partition tree generation, the CU block and its four partitioned child-blocks need to become PU and TU for calculating the coding rate-distortion cost. This process requires more execution time from the processor because of highly repeated computations on PUs and TUs before finding the best quad-tree partition tree. The proposed prediction technique is based on edge information from the content of the considered CU and the depth information of partition tree from the co-located CU in the neighboring video frames for being able to adapt the reduction of computation time with the varying content in the incoming frames. When the CU is in a smooth frame, the information from the neighboring frames would dominate the prediction results of the partition tree; however, the edge information of the current CU mainly determines the partition tree. With the prediction technique, experiments on several benchmark videos show that the encoding time of HEVC can be reduced by 44.1 % at an acceptable degradation of coding efficiency.

High Efficiency Video Coding (HEVC), which is the newest video coding standard, has been developed for the efficient compression of ultra high definition videos. One of the important features in HEVC is the adoption of a quad-tree based video coding structure, in which each incoming frame is represented as a set of non-overlapped coding tree blocks (CTB) by variable-block sized prediction and coding process. To do this, each CTB needs to be recursively partitioned into coding unit (CU), predict unit (PU) and transform unit (TU) during the coding process, leading to a huge computational load in the coding of each video frame. This paper proposes to extract visual features in a CTB and uses them to simplify the coding procedure by reducing the depth of quad-tree partition for each CTB in HEVC intra coding mode. A measure for the edge strength in a CTB, which is defined with simple Sobel edge detection, is used to constrain the possible maximum depth of quad-tree partition of the CTB. With the constrained partition depth, the proposed method can reduce a lot of encoding time. Experimental results by HM10.1 show that the average time-savings is about 13.4% under the increase of encoded BD-Rate by only 0.02%, which is a less performance degradation in comparison to other similar methods. All Rights Reserved © 2015 Universidad Nacional Autonoma de Mexico, Centro de Ciencias Aplicadas y Desarrollo Tecnologico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0.

Three Cu- and Ag-based metal–organic frameworks (MOFs) with different crystal structures from the same ligand CA (CA = 4-pyranone-2,6-dicarboxylic acid), {[Cu(CA)]·CH3CN}n (1), {[Cu(CA)(H2O)2]·H2O}n (2), and [Ag2(CA)]n (3) have been synthesized under solovthermal conditions. Crystal structures of all the compounds possessing the same crystal nonpolar point group of 2/m were determined by single-crystal X-ray diffraction analysis. Compound 1 has a (3,6)-connected three-dimensional (3D) rtl framework with (4·62)2(42·610·83) Schlafli topology based on binuclear secondary building units equivalent to a paddle wheel. Compound 2 features a (3,3)-connected two-dimensional (2D) fes (4·82) layer, which is further extended to a 3D supramolecular network by interlayer hydrogen bonds. Compound 3 is a rare 3D framework with a (46)2(49·618·8) topological symbol without solvent molecules, which contains three rings that are 14-member, 10-member, and 8-member, respectively. Moreover, the dielectric properties and mechani...

Octa-pinene substituted double-decker lanthanide(III) phthalocyanines LnPc*2 (Ln = Eu, Er, Lu) were prepared and their spectral, electrochemical, spectroelectrochemical and electrochromatic properties were studied. The introduction of the bulky and rigid pinene groups into phthalocyanines provides several advantages for the resulting double-decker lanthanide(III) phthalocyanine complex. First of all, the intermolecular interaction in the new LnPc*2 complex was weakened, leading to excellent solubility. Secondly, intramolecular distances between the macrocycles in LnPc*2 molecules were also increased, resulting in a significant red shift of the ring-to-ring intervalence charge transfer bands. Particularly, the intervalence bands of EuPc*2, ErPc*2 and LuPc*2 were observed at 1944, 1693 and 1620 nm, respectively, which appear to be the most red-shifted absorption in comparison with the literature values of mononuclear double-decker Eu(III), Er(III) and Lu(III) phthalocyanines. Thirdly, given the red-shifted near-IR (NIR) absorption and the various colorful oxidation states, the solution of LnPc*2 exhibits electrochromic behavior both in the UV-Vis and near-IR regions. Notably, spectral change of EuPc*2 covers almost the whole range of the NIR region. Finally, the pinene groups also enhance the film-forming ability. Therefore, we were able to fabricate solid state electrochromic devices through a solution processable method. The as-fabricated devices show reversible electrochromic behavior with high color efficiency and good stability.

A couple of enantiomeric chiral cyclometalated platinum(II) complexes [Pt((−)-L1)(Dmpi)]Cl ((−)-1) and [Pt((+)-L1) (Dmpi)]Cl ((+)-1) [(−)-L1 = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L1 = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide] were synthesized. Two polymorphs (Form-Y and Form-R) of the complex (−)-1 were obtained. The crystallographic studies of both forms revealed that the emission and electronic circular dichroism (ECD) spectra of these complexes at solid state were sensitive to the intermolecular effects and to the molecular surrounding environments. The yellow forms (Form-Y) of the complexes (−)-1 and (+)-1 were found to undergo crystal-to-amorphous transformation upon mechanical grinding, resulting in luminescent and chiroptical switching behaviours as evidenced by emission and ECD spectra. The mechanochromic process can be reversed repeatedly by the addition of a few drops of dichloromethane. When the counteranion Cl− in 1 was replaced with trifluoromethanesulfonate (OTf−), complexes [Pt((−)-L1)(Dmpi)]OTf ((−)-2) and [Pt((+)-L1)(Dmpi)]OTf ((+)-2) were obtained. Complexes (−)-2 and (+)-2 showed a more pronounced luminescent switching behaviour, suggesting that the switching properties can be tuned by the counteranions.

A new compound containing both 3,4-dithienylpyrrole (DTP) and triphenylamine (TPA) groups, namely, 4′-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-N,N-diphenylbiphenyl-4-amine (DTP-Ph-TPA), was designed and synthesized. The polymer poly-DTP-Ph-TPA (PDTP-Ph-TPA) was prepared by electropolymerization from DTP-Ph-TPA. When the applied potential circulates from 0.0 V to 1.4 V, the polymer not only exhibits reversible multicolor in the visible region (yellow, light green, magenta and blue), but also shows excellent electrochromic properties in the NIR region with high contrast ratio (ΔT = 70.5% in 1550 nm, ΔT = 67.9% in 1310 nm) and a very short response time (about 1.4 s for 1550 nm, 0.9 s for 1310 nm). A single layer electrochromic device (ECD) based on polymer PDTP-Ph-TPA was constructed and characterized.

A B S T R A C T Two series of Cardo-type polyimides (PIs), fluorinated or nonfluorinated, were prepared from condensation of the fluorinated Cardo-type diamine 1,1-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]cyclopentane (BATFPCP) or the analogous nonfluorinated Cardo-type diamine 1,1-bis[4-(4aminophenoxy)phenyl]cyclopentane (BAPCP) with four aromatic dianhydrides PMDA, ODPA, BTDA and BPDA, respectively. Both fluorinated and nonfluorinated PIs with Cardo-structure in polymer backbone generally retained good thermal properties comparable to aromatic PIs, with glass transition temperature (Tg) of 227–270 8C and 234–340 8C, 5% weight loss temperature in nitrogen (air) of 471–483 8C (448–474 8C) and 472–482 8C (464–492 8C), respectively. The fluorinated and nonfluorinated PIs with Cardo-structure in the polymer backbone showed tensile strengths of 90.1–101.7 MPa and 78.6–99.6 MPa, tensile modulus of 1.44–1.83 GPa and 1.25–1.50 GPa, respectively, also comparable to those of the traditional aromatic PIs. In comparison with nonfluorinated series, the fluorinated PIs possessed better solubility, higher optical transparency and lower water absorption. The fluorinated PIs were readily soluble in a variety of organic solvents, exhibited high optical transparency and light color with the cut off wavelength at 373–424 nm and transmittance at 500 nm generally higher than 80%, and the water absorptions were measured as low as 0.18–0.93%. Additionally, the fluorinated series showed higher hydrophobicity by water contact angles and water absorption measurements and lower dielectric constant by dynamic dielectric measurements.

Grain size and lubricating conditions influence material flow behaviours in micro metal forming processes. In this study, the brass (JIS C2700) tubes with 1.1 mm outer diameter and 0.5 mm inner diameter were treated by annealing at 400 °C, 500 °C and 600 °C to obtain various microstructures with the grain sizes of 20 μm, 34 μm and 80 μm, respectively. The treated tubes were machined and grounded to be 0.6 mm length specimens for the experiments of micro forward and backward hollow extrusion. Three lubricating conditions, which were dry, full and punch lubricated conditions, were carried out in the experiments. By comparing the upper cup height and rod length of the extruded specimens with the calibration curves established by finite element simulations, it is possible to estimate the friction factors in the processes. The results show that the dry conditions lead to stronger friction effects and thus larger friction factors. Moreover, the friction factor increased with grain size and stroke for all conditions.

A series of novel fluorinated alicyclic-functionalized polyimides (FPI- x ) were prepared from a new alicyclic-functionalized diamine, 1,3-bis ((4-amino-2-(trifluoromethyl)phenoxylmethylene)-1,2,2-trimethyl cyclopentane (BAFMT), which was derivated from natural-(D)-camphor via multi-step process. The influence of the presence of the alicyclic and fluorinated structure on the general properties of the polymers was systematically investigated in terms of optical, thermal and mechanical properties, solubility and hydrophobicity, rendering the general structure–properties relationships for the FPI- x . Compared with the analogous control aromatic polyimide NPI- x , FPI- x shows better solubility, improved optical transparency, lower moisture absorption and surface energy, owing to the presence of the fluorine-containing group and alicyclic structure in the polymer chain. Although presenting a slight decrease as compared with NPI- x , the good thermal stability of polyimide was retained on the large in the fluorinated alicyclic-functionalized polymer FPI- x , with T g ranging in 197–233 °C and T d5 ranging in 374–420 °C. A particular research emphasis were placed on employing the dielectric relaxation technique to study the dielectric constant (e′), dielectric loss (e″) and electric modulus (M″) of the fluorinated alicyclic-functionalized polyimide film FPI-4 and its control sample NPI-4. The observed dielectric relaxations have been fully studied by integrating the contributions of the specific structure and functional groups. It is revealed that the presence of fluorinated alicyclic-functionalized group endows FPI-4 with lower dielectric constant e′ (2.88 at 1 MHz and 25 °C) and dielectric loss e″ (0.0058 at 1 Hz and 25 °C) than NPI-4 (3.49 and 0.0084) and commercial Kapton HN (3.19 and 0.006) with the same measurement frequency and temperature.

A new self-healing polymer has been obtained by incorporating a cyclometalated platinum(II) complex Pt(C∧ N∧ N)Cl (C∧ N∧ N = 6-phenyl-2,2'-bipyridyl) into a polydimethylsiloxane (PDMS) backbone. The molecular interactions (a combination of Pt···Pt and π-π interactions) between cyclometalated platinum(II) complexes are strong enough to crosslink the linear PDMS polymer chains into an elastic film. The as prepared polymer can be stretched to over 20 times of its original length. When damaged, the polymer can be healed at room temperature without any healants or external stimuli. Moreover, the self-healing is insensitive to surface aging. This work represents the first example where the attractive metallophilic inter-actions are utilized to design self-healing materials. Moreover, our results suggest that the stretchability and self-healing properties can be obtained simultaneously without any conflict by optimizing the strength of crosslinking interactions.

A novel europium(iii) complex simultaneously exhibiting photocolorimetric and photofluorometric behavior was obtained. Multiple distinguishable identities can be obtained and reversibly modulated using light as external stimuli. With this novel photo-responsive complex, double encryption and advanced anti-counterfeiting were realized.

Combining stretchability and self-healing properties in a man-made material is a challenging task. For an efficient self-healing material, weaker dynamic or reversible bonds should be presented as crosslinks so that they will first break upon damage and then reform after healing, which is not favorable when developing elastic materials. In this work, by incorporating dynamic Fe(III)-triazole coordination bonds into polydimethylsiloxane (PDMS) backbone, a highly elastic polymer is obtained that can be thermally healed at mild temperature. The as-prepared polymer can be stretched to 3400% strain at low loading speed (1 mm min(-1) ). When damaged, the polymer can be thermally healed at 60 °C for 20 h with a healing efficiency of over 90%. The good mechanical and healable properties of this polymer can be ascribed to the unique coordination bond strength and coordination conformation of Fe(III)-triazole coordination complex.

Adopting self-healing, robust, and stretchable materials is a promising method to enable next-generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self-healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self-healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal-coordinated bonds (β-diketone-europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self-healing and exhibits excellent elasticity. The polymer network forms a microphase-separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self-healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self-healable dielectric layer is fabricated with a dual-dynamic bonding polymer system and self-healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self-healable touch pad.