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Carbon nanofillers are widely used to blend with polymers for fabricating high-performance polymer nanocomposites (PNCs) toward structural, electronic and sensory material applications. However, it is generally of challenge to achieve significant property improvement by using single carbon nanofiller. Alternatively, using hybrid carbon nanofillers has been proved to be a facile and promising strategy to effectively boost electrical and piezoresistive properties of PNCs. This paper provides a state of the art review on the effects of hybrid carbon fillers on electrical properties of PNCs and corresponding applications in piezoresistive sensing scenarios. The effects of hybrid carbon nanofillers on electrical percolation threshold, electrical conductivities and piezoresistive sensitivity of PNCs are systematically discussed.

The novel vitrimerization concept of converting permanently cross-linked networks of thermoset polymers into dynamic exchangeable networks often relies on transesterification reactions. Transesterification exchange reactions, for example, in epoxy vitrimers, are usually contingent on equivalent ratios of hydroxyl to ester groups and large amounts of catalysts to achieve proper dynamic exchange capability. In general, postconsumer epoxy cured with anhydrides contains very few hydroxyl groups in the network, and it is challenging to convert it into efficient dynamic networks by vitrimerization. Here, we demonstrate that introducing cellulose nanocrystals as feedstock of external hydroxyl groups in the mechanochemical vitrimerization process could improve the exchange reaction rate as well as the thermomechanical properties of the vitrimerized epoxy. This work offers an effective way to recycle and reprocess postconsumer epoxy/anhydride waste with inherent low ratios of hydroxyl to ester groups into higher value-added vitrimer nanocomposites.

An increasing utilization of flexible healthcare electronics and biomedicine-related therapeutic materials urges the development of multifunctional wearable/flexible smart fabrics for personal therapy and health management. However, it is currently a challenge to fabricate multifunctional and on-body healthcare electronic devices with reliable mechanical flexibility, excellent breathability, and self-controllable joule heating effects. Here, we fabricate a multifunctional MXene-based smart fabric by depositing 2D Ti3C2Tx nanosheets onto cellulose fiber nonwoven fabric via special MXene-cellulose fiber interactions. Such multifunctional fabrics exhibit sensitive and reversible humidity response upon H2O-induced swelling/contraction of channels between the MXene interlayers, enabling wearable respiration monitoring application. Besides, it can also serve as a low-voltage thermotherapy platform due to its fast and stable electro-thermal response. Interestingly, water molecular extraction induces electrical response upon heating, i.e., functioning as a temperature alarm, which allows for real-time temperature monitoring for thermotherapy platform without low-temperature burn risk. Furthermore, metal-like conductivity of MXene renders the fabric an excellent Joule heating effect, which can moderately kill bacteria surrounding the wound in bacteria-infected wound healing therapy. This work introduces a multifunctional smart flexible fabric suitable for next-generation wearable electronic devices for mobile healthcare and personal medical therapy.

International audience; Dielectric nanomaterials offer great promise for diverse technological applications such as capacitors, actuators, and sensors. Unfortunately, the exploitation of desirable dielectric properties in polymer nanocomposites is a great challenge due to lack of efficient routes to achieve uniform dispersion of nanoparticles and good compatibility of interfaces at high nanoparticle loadings. A dilemma between the nanofiller loading and dispersion as well as interfacial compatibility makes it impossible to fully exploit the intrinsic polarization of the nanoparticles. Herein, we solve such a dilemma and fabricate highly filled barium titanate/silicone rubber (BT/SR) nanocomposites through chemically bonding BT nanoparticles with SR by “thiol–ene click” and isostatic pressing techniques. BT loading varies from 88 wt% to 97 wt% without compromising the uniform dispersion quality and good interfacial adhesion with the SR matrix. The 90 wt% BT nanocomposite shows an optimum dielectric constant as high as 55, while its loss tangent can be kept as low as 0.019 at 103 Hz. Meanwhile, it displays good stability of dielectric properties from room temperature up to 100 °C. In addition, the breakdown strength just decreases slightly compared to neat SR (97 MV m−1) but is still beyond 75 MV m−1. The present work provides a facile strategy towards superior dielectric polymer nanocomposites.

As a renewable and environment-friendly technology for seawater desalination and wastewater purification, solar energy triggered steam generation is attractive to address the long-standing global water scarcity issues. However, practical utilization of solar energy for steam generation is severely restricted by the complex synthesis, low energy conversion efficiency, insufficient solar spectrum absorption and water extraction capability of state-of-the-art technologies. Here, for the first time, we report a facile strategy to realize hydrogen bond induced self-assembly of a polydopamine (PDA)@MXene microsphere photothermal layer for synergistically achieving wide-spectrum and highly efficient solar absorption capability (≈ 96% in a wide solar spectrum range of 250–1,500 nm wavelength). Moreover, such a system renders fast water transport and vapor escaping due to the intrinsically hydrophilic nature of both MXene and PDA, as well as the interspacing between core-shell microspheres. The solar-to-vapor conversion efficiencies under the solar illumination of 1 sun and 4 sun are as high as 85.2% and 93.6%, respectively. Besides, the PDA@MXene photothermal layer renders the system durable mechanical properties, allowing producing clean water from seawater with the salt rejection rate beyond 99%. Furthermore, stable light absorption performance can be achieved and well maintained due to the formation of ternary TiO2/C/MXene complex caused by oxidative degradation of MXene. Therefore, this work proposes an attractive MXene-assisted strategy for fabricating high performance photothermal composites for advanced solar-driven seawater desalination applications.

Piezoelectric materials, a type of “smart” material that generates electricity while deforming and vice versa, have been used extensively for many important implantable medical devices such as sensors, transducers, and actuators. However, commonly utilized piezoelectric materials are either toxic or nondegradable. Thus, implanted devices employing these materials raise a significant concern in terms of safety issues and often require an invasive removal surgery, which can damage directly interfaced tissues/organs. Here, we present a strategy for materials processing, device assembly, and electronic integration to 1) create biodegradable and biocompatible piezoelectric PLLA [poly(l-lactic acid)] nanofibers with a highly controllable, efficient, and stable piezoelectric performance, and 2) demonstrate device applications of this nanomaterial, including a highly sensitive biodegradable pressure sensor for monitoring vital physiological pressures and a biodegradable ultrasonic transducer for blood–brain barrier opening that can be used to facilitate the delivery of drugs into the brain. These significant applications, which have not been achieved so far by conventional piezoelectric materials and bulk piezoelectric PLLA, demonstrate the PLLA nanofibers as a powerful material platform that offers a profound impact on various medical fields including drug delivery, tissue engineering, and implanted medical devices.

Dynamics of exchange within vitrimer networks are influenced by mobility of the chemical species involved in the exchange reaction, then it can be affected by the crystalline phase when boronic ester bond is introduced into the thermoplastic elastomers with crystalline phase as physical cross-links. In this work, the dynamic dioxaborolane cross-links were introduced into commercial poly(ethylene-α-octene) (POE) with crystalline phases as physical cross-links to prepare POE vitrimers. The results of stress relaxation show that relaxation time (τ) follows an Arrhenius law with the temperature at the melting range for not only POE vitrimers and thermally treated POE vitrimers with dynamic cross-links, but also neat POE with purely physical cross-links. The liquid-to-solid transition temperature can raise to 35.3 °C for POE vitrimers from -42.9 °C of the thermally treated one, due to the constrained mobility by residual crystalline phases. The resulted POE vitrimers maintain a stress at break of higher than 27.5 MPa and an elongation at break of higher than 800% at room temperature. With the temperature increasing, the crystal melting induced weakening of the physical cross-linking in POE decreases the strength, but the storage modulus and the stress at 300% and 500% elongation of POE vitrimers are improved. The properties of POE vitrimers can almost keep unchanged after recycling or healing. All these results show that the introduction of reversible boronic ester bonds is a promising strategy to improve the performances and recyclability of physically cross-linked POE materials.

Solar-driven interfacial water evaporation is regarded as an effective, renewable, and environment-friendly technology for clean water production. However, biofouling caused by the nonspecific interaction between the steam generator and biofoulants generally hinders the efficient application of wastewater treatment. Herein, this work reports a facile strategy to fabricate flexible anti-biofouling fibrous photothermal membrane consisting of a MXene-coated cellulose membrane for highly efficient solar-driven water steam evaporation toward water purification applications. The as-prepared MXene/cellulose photothermal membrane exhibits light absorption efficiency as high as ∼94% in a wide solar spectrum range and a water evaporation rate up to 1.44 kg m-2 h-1 under one solar illumination. Also, the MXene/cellulose membrane shows very high antibacterial efficiency (above 99.9%) owing to the MXene coating as a highly effective bacteriostatic agent. Such a flexible, anti-biofouling, and high-efficiency photothermal membrane sheds light on practical applications in long-term wastewater treatments.

Electrically conductive polymer composites (CPCs) are potential alternatives to conventional strain gauges due to their tunable sensitivity and strain ranges. Currently, to achieve very high piezoresistive sensitivity in thermoplastic-based CPCs with Gauge factors

Reversible shape-memory polymers (RSMPs) show great potential in actuating applications because of its repeatability among many other advantages. Indeed, in many cases, multiresponsive RSMPs are more expected, and the strategy to introduce functional fillers without deteriorating the reversible deformation performance is of great importance. Here, a facile strategy to balance the electro, photothermal performance, and molecular chain mobility is reported. Segregated conductive networks of carbon nanotubes (S-CNTs) are constructed in the poly(ethylene

Electrically conductive thermoplastic polyurethane (TPU) composites with carbon nanofillers have potential applications in strain sensors. However, it is challenging to simultaneously achieve low percolation threshold, good electrical conductivity and high strain sensitivity especially in melt-mixed TPU-carbon filler nanocomposites. Here, we report on using branched carbon nanotubes known as carbon nanostructures (CNS) in melt-mixed TPU composites. These composites have an electrical percolation threshold (ΦC) of 0.82 wt%, whereas when using multiwall carbon nanotubes (CNT) the ΦC is 3.02 wt%. Based on linear fitting, the TPU nanocomposite with 2 wt% CNS shows gauge factors of 15, 30 and 58 for strain levels of 0–44%, 45–73% and 74–100%, respectively, by comparison with the 5 wt% CNT nanocomposite, which exhibits a gauge factor of 18 for strain 0–100%. These composites show potential strain-sensing applications in detection of joint bending and muscle exercise. This study reveals the effects of CNT morphology on polymer composite properties, enhancing the understanding of structure-property relationship for polymer nanocomposites.

Elastomers with high dielectric constant and low loss have potential applications in energy storage and conversion devices, and the study of dielectric-temperature dependence for dielectric elastomers is of great significance. Here, we report on a strategy to tune dielectric constant and loss of thermoplastic polyurethane (TPU) composites by using hybrids of carbon nanostructures (CNS, also known as branched carbon nanotubes) and graphene nanoplatelets (GNP). At the same filler content, CNS have a greater contribution to the total dielectric constant than GNP, however it is accompanied by a larger loss tangent. By contrast, using a CNS-GNP hybrid results in improved dielectric properties, i.e. high dielectric constant and low loss tangent for a wide temperature range, as well as the same elongation at break as neat TPU. Additionally, the dielectric-temperature dependence for TPU/CNS composites enables the potential applications for temperature sensors by correlating temperature with dielectric constant. This study enhances understanding of the effect of filler type and temperature on dielectric properties of TPU composites, as well as their mechanical properties, introducing an effective strategy for the property optimization of dielectric elastomers as functional materials for sensor and actuator applications.

As dynamic cross-linking networks are intrinsically weaker than permanent covalent networks, it is a big challenge to obtain a stiff self-healing polymer using reversible networks. Inspired by the self-healable and mechanically adaptive nature of sea cucumber, we design a water-responsive self-healing polymer system with reversible and permanent covalent networks by cross-linking poly(propylene glycol) with boroxine and epoxy. This double cross-linked structure is self-healing due to the boroxine reversible network as well as showing a room-temperature tensile modulus of 1059 MPa and a tensile stress of 37 MPa, on a par with classic thermosets. The dynamic boroxine bonds provide the self-healing response and enable up to 80% recovery in modulus and tensile strength upon water contact. The system shows superior adhesion to metal substrates by comparison with the commercial epoxy-based structural adhesive. Besides, this system can change modulus from a stiff thermoset to soft rubber (by a factor of 150) upon water stimulus, enabling potential applications of either direct or transform printing for micro/nanofabrication. Moreover, by incorporating conductive nanofillers, it becomes feasible to fabricate self-healing and versatile strain/stress sensors based on a single thermoset, with potential applications in wearable electronics for human healthcare.

Piezoresistive strain sensors for structural health monitoring (SHM) and human body motion detection applications commonly use polymer nanocomposites based on carbon fillers such as carbon black (CB), carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). Here, we report on new nanocomposites from thermoplastic polyurethane (TPU) with branched carbon nanotubes (known as carbon nanostructures (CNS)) as well as hybrid fillers (CNS + CNT or CNS + GNP) with superior electrical conductivity. These composites manufactured by melt mixing show also exceptional piezoresistive sensitivity. As an example, at only 2 wt% filler concentration, the TPU/CNS and TPU/CNS/GNP nanocomposites have a gauge factor (GF) up to 28 and 144, respectively, under 50% strain (very low for elastomers), which is currently the highest reported values for TPU composites with carbon nanofillers. This study sheds light on the effects of filler morphological structure on electrical conductivity and piezoresistive sensitivity of polymer nanocomposites, introducing a new strategy to prepare multifunctional polymer nanocomposites with very high piezoresistive sensitivity for SHM and body motion detection applications.

In this study, metallocene linear low density polyethylene (abbreviated as mPE) was grafted with glycidyl methacrylate (GMA) and acrylic acid (AAc) forming long-chain branched polymers, which act as an interfacial modifier of recycled high-density polyethylene (abbreviated as rPE)/low-density polyethylene (LDPE) blends. AAc was shown to increase GMA grafting efficiency onto mPE producing mPE-g-GMA/AAc. The mechanical properties, crystalline structure, rheological properties, and phase structure of rPE/LDPE/mPE-g-(GMA-co-AAc) (abbreviated as rPE/LDPE/mPE-g-G/A) blends were investigated using uniaxial tensile, differential scanning calorimeter, rheometer, and X-ray diffraction experiments. The tensile strength of rPE/LDPE/mPE-g-G/A was 34.51 MPa and the multiphase polymer displayed co-crystallization characteristics indicating good compatibility between the two components. The changes in the interface layer thickness and dispersed phase size further indicate the existence of partial compatibility among the multiphase polymer.

A spherical blue CoAl2O4 pigment powder commonly used for coloring ceramic products has successfully been synthesized by co-precipitation of Co2+ and Al3+ ions in Pickering emulsion assisted with a hydrothermal process, and the formation mechanism of the as-prepared powder has briefly been discussed. The effects of pH condition on the crystalline phase and color tone of the pigment powder were investigated at 280 °C by varying the pH value of the reaction system. Then, under an optimized pH condition to produce blue, the pigment powder was synthesized still hydrothermally at different temperatures (210, 240, 270 and 300 °C) to assess the effect of hydrothermal reaction temperature on the pigment particle morphology. The resulting pigment powders were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), CIELAB colorimetric analysis (CIE-L∗a∗b∗), laser particle size analysis (LPS), and N2-adsorption measurement (BET). FE-SEM and TEM observations indicated that the pigment powders of spherical shape obviously were constructed by a core–shell double-layer structure, the radii of which all were ∼150 nm or so with a shell of ∼25 nm in thickness. XRD results demonstrated that the pigment powders that were obtained from the aforementioned method under a wide range of pH values invariably contained basically crystalline CoAl2O4 of high purity. CIE-L∗a∗b∗ data suggested that the pigment powders at 280 °C and pH ≤ 11.2 appeared different chromas of bluish colors compared with that displaying black which was obtained at pH = 12.3. LPS and BET results showed that the CoAl2O4 pigment powder prepared under the urea concentration of 3.6040 g for 24 h at the hydrothermal temperatures of 240 °C exhibited a narrow particle size distribution, the specific surface area of which was evaluated to be ∼56.4 m2/g.

Measuring vital physiological pressures is important for monitoring health status, preventing the buildup of dangerous internal forces in impaired organs, and enabling novel approaches of using mechanical stimulation for tissue regeneration. Pressure sensors are often required to be implanted and directly integrated with native soft biological systems. Therefore, the devices should be flexible and at the same time biodegradable to avoid invasive removal surgery that can damage directly interfaced tissues. Despite recent achievements in degradable electronic devices, there is still a tremendous need to develop a force sensor which only relies on safe medical materials and requires no complex fabrication process to provide accurate information on important biophysiological forces. Here, we present a strategy for material processing, electromechanical analysis, device fabrication, and assessment of a piezoelectric Poly-l-lactide (PLLA) polymer to create a biodegradable, biocompatible piezoelectric force sensor, which only employs medical materials used commonly in Food and Drug Administration-approved implants, for the monitoring of biological forces. We show the sensor can precisely measure pressures in a wide range of 0-18 kPa and sustain a reliable performance for a period of 4 d in an aqueous environment. We also demonstrate this PLLA piezoelectric sensor can be implanted inside the abdominal cavity of a mouse to monitor the pressure of diaphragmatic contraction. This piezoelectric sensor offers an appealing alternative to present biodegradable electronic devices for the monitoring of intraorgan pressures. The sensor can be integrated with tissues and organs, forming self-sensing bionic systems to enable many exciting applications in regenerative medicine, drug delivery, and medical devices.

Interfacial solar steam generation is a water treatment strategy without liquid waste discharge that minimizes the environmental impact of wastewater. For practical applications especially large scale applications on the sea with harsh environment, excellent mechanical strength and economic manufacturability of the evaporator is essential. Herein, we choose a straightforward, scalable and controllable polymer processing method to manufacture porous poly(ethylene-co-octene) elastomers (pPOE). The pore sizes and porous structure of pPOE are dynamically controlled by annealing treatment. For the bottom-up evaporation device, the water transport capacity substantially influences the evaporation performance. With the aid of finite volume simulation, the adjustable porous POE elastomers with different water transport capabilities are used to analyze the effect of water transport on evaporation performance, and the porous POE elastomer with optimal pore size is preferably used for steam generation. This POE-based evaporator with suitable water supply capacity exhibits excellent evaporation performance and outstanding mechanical strength, showing great potential to achieve low-cost sustainable seawater desalination and wastewater purification.

Transmission electron microscopy (TEM), with the high spatial and temporal resolution, is widely used in nano material characterizations. Due to the vacuum compatibility issue, traditional TEM is mostly used for solid and dry samples. The progress of nano science involves a wide range of liquid environments, and the development of in situ liquid chamber TEM technologies has made it possible for real time dynamic analysis on samples in liquid environments, with nanometer scale imaging resolutions, and greatly expanded the application ranges of TEM. This field has now brought much attention internationally, and is currently growing with a very rapid speed. In this paper, we review the progress about in situ liquid chamber TEM that our group has participated in and/or carried out in the recent years. It includes the development of the in situ liquid chamber TEM experiment apparatus, and its applications in the fields of nano-material preparations and characterizations, electrochemical reaction processes, new energy materials and devices, and life sciences. At last, the future development trend of in situ liquid chamber TEM is prospected. Firstly, some in situ liquid chamber TEM experiment apparatuses have been developed. These in situ chambers are home-made, based on metal cages and O-ring seals, which allow silicon nitride window substrates to be quickly assembled together, with liquid samples sealed inside. Besides simple imaging, electrochemical and heating-cooling functions have been incorporated into the setups, allowing for more advanced analyses. Using these in situ TEM apparatus, several nano material and reaction systems have been monitored. A sliver particle aqueous solution sample has been characterized. The particles were observed to be about 5–18 nm, attached to the Si3N4 windows, and could not be able to move freely in the liquid. Fine structures within single particles could be clearly seen. Bubbles commonly exist in an in situ liquid chamber, which are important for effectively reducing the local liquid layer thickness and enhancing the imaging resolution. In Au particle aqueous solution sample, particle and particle cluster motions have been further observed. The results show that particles in a cluster gradually fused together with time. For Au/AgCl composite nanocube sample, more dramatic electron beam effect has been seen, and the nanocubes were transformed quickly into hollow structures. By means of a liquid phase electron beam induced deposition (LP-EBID) approach, Si and SiC x nano structures have been made with in situ liquid chamber TEM. Nano dots, nano lines and three-dimensional nano structures can be controllably made by adjusting the electron beam exposure conditions. Secondary electron effects are attributed to the nano structural growth mechanism. Choosing Ni/NiCl2 system, both electrochemical deposition and etching of the nickel nano films have been observed by applying electric biases of different polarities to the nickel electrodes in the in situ chamber. Instead of extensional growth on existing crystals, it is more commonly observed that new nickel nano particles grow out in front of the existing film first and then merge into the film. During electrochemical etching, holes form in the Ni films due to Rayleigh instability. The structures of E. coli cells in aqueous solutions have been studied. Most of the cells remaine intact under the electron beam irradiation, Pili motions have been observed in the TEM imaging. Fluorescent imaging data confirm that the cells can keep alive after long time electron bean irradiation during the experiment. In situ liquid chamber TEM has opened up a new way for conducting research in nano science, new energy materials and devices, life sciences, involving liquid environments. In the future, it is expected that advanced functions of the in situ liquid chamber TEM will be further developed, and the application scope will be further expanded.

Titanium dioxide nanowire membranes have been synthesized by a hydrothermal growth on the surfaces of Ti substrates in a 12 M NaOH aqueous solution at 160 °C for 24 h, followed by ion-exchange with 0.5 M HCl aqueous solution and subsequent heat treatment such as calcination or a second hydrothermal treatment. The as-prepared TiO2 nanowires as well as their precursor were characterized by field emission scanning electron microscopy (FE-SEM), thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, ultraviolet-visible (UV-Vis) spectrophotometry, transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectrometry. FE-SEM observations indicated that the TiO2 nanowires were 50–250 nm in diameter and up to several dozens of microns in length. TG-DTA and XRD results demonstrated that the crystalline phases of the nanowires obtained from calcinations of their precursor at different temperatures above 350 °C consisted mostly of anatase. BET, UV-Vis, TEM and EDX results showed that the nanowires obtained upon calcination of their precursor at 550 °C had the greatest degradation efficiency for Rhodamine-B, and that, at the same temperature of 250 °C, the hydrothermal treatment process of TiO2-precursor nanowires had a more significant effect on the photocatalytic activity of the resulting TiO2 nanowires than the calcination.

Fabrication of flexible strain sensors incorporating superlight and robust conductive skeletons in a facile and environmentally friendly manner poses a number of processing challenges. Herein, we report a novel, low-density, three-dimensional conductive filler skeleton consisting of natural psyllium and conductive carbon nanostructure (CNS, i.e. branched carbon nanotubes). After infiltration of polydimethylsiloxne (PDMS) into the skeleton, a composite with excellent electrical conductivity and superior piezoresistive sensitivity was obtained. Psyllium assists the formation of a conductive CNS network, thus the composite made by the skeleton exhibits electrical conductivity up to 6.6 S/m for only 0.2 wt% CNS. Skeletons composed with 0.2 wt% CNS and various content of psyllium infiltrated with PDMS have a linearly responsive gauge factor between 2.3 and 4.5. Continuous psyllium- CNS pathways not only enhance electron transport within composites, but the psyllium also provide extra mechanical support to ensure stable and reproducible strain sensing in the composite. Potential applications of the composites as control switches and for motion detection are reported.

Cellulose is one of the most promising fillers used for poly(lactic acid) (PLA) composites owing to its natural abundance, complete biodegradability, and superb properties. Improving the compatibility between hydrophilic cellulose and hydrophobic PLA is a hot topic in literature for a long time, wherein surface chemical modification of cellulose have attracted the most attention. In this review, we summarized the research activities of recent five years that focus on the chemical modification strategies of cellulose used in PLA/cellulose composites. Two major classifications are carefully discussed, i.e., the reactions of small molecules modified cellulose such as esterification, oxidation/amidation and silanization, and reactions of polymers modified cellulose including PLA and other polymers. The discussion mainly focuses on the relationship between the structure of grafted small molecule/polymers and mechanical properties of PLA composites and addresses the current common problems that hinder the chemical modified cellulose from developing high-performance PLA/cellulose composites. We hope this review provide some possible inspiration for researchers to develop PLA/cellulose products with industrial value in the future.

Piezoelectric film pressure sensors are forthcoming choices for self-powered flexible and portable electronics because of their unique advantages in instant response and linear pressure-electrical signal relationship. However, it is commonly of challenge to achieve high output voltage response to pressure in piezoelectric polymer films. Here, we report a piezoelectric film pressure sensor fabricated by electrospun polyvinylidene-fluoride-trifluoroethylene (PVDF-TrFE)/MXene nanofiber mats. As a new two-dimensional nanomaterial, MXene has not only a large amount of surface functional groups to enable interaction with the dipoles of PVDF-TrFE molecular chains, but also high electrical conductivity to potentially increase the polarization of PVDF-TrFE during electrospinning. As such, by comparison with the control pressure sensor consisting of neat PVDF-TrFE film, the composite film sensor shows significantly improved output voltage, and the improvements are closely dependent on MXene content. For instance, the composite film with 2.0 wt% MXene can achieve an instantaneous output power density of ~3.64 mW/m2 under the pressure of 20 N with the frequency of 1 Hz. Such piezoelectric PVDF-TrFE/MXene films are capable of sensing body motion for healthcare. Furthermore, the hydrophilicity of MXene allows the film pressure sensor to monitor humidity change, thus the composite film sensor demonstrates potential application in multifunctional electronic skins.

As a widely-used engineering thermoplastic, polyamide 6 (PA6) is prone to hydrolysis in acidic and alkaline solvents, precluding its application in both acidic and alkaline environments. Polymer blending is an interesting strategy to fabricate high-performance polymer composites, while it is of challenge to achieve satisfactory properties via simple polymer blending technologies. Here, we report a chemical-resistant PA6/Polyketone (PK) composite with gradient encapsulation structures that is available by both high-pressure capillary extrusion and injection molding. Processing conditions including interfacial tension, viscosity ratio of polymer pairs, and shear rate during melt processing were taken into account to study the formation mechanism of such a special structure. It was revealed that the gradient encapsulation structure can be formed at a critical shear rate of beyond 200 s−1 and the critical viscosity above 5.8. Owing to the interesting gradient encapsulation structure (PK sheath and PA core), the obtained PA6/PK composites showed superior chemical-resistant performance upon formic acid immersion due to the formation of PK “sheath”. This work provides a facile strategy to fabricate PA6 materials with outstanding chemical resistance and mechanical properties by rapid and scalable melt processing methods.

Great progresses have been achieved in paper-like highly thermally conductive films with high in-plane thermal conductivity (k), but their applications are still limited by the unsatisfactory through-plane k (0.05–2 Wm−1K−1). In practical applications, paper-like robust composites with high through-plane k, instead of bulk materials, are highly desired for thermal interface materials (TIMs). In this work, flexible bacterial cellulose (BC) based paper-like composites with an ideal-thermal-transportation structure, in which a single-layer Al2O3 particles are confined in the through-plane direction of the films and the Al2O3 particles are covered by highly thermally conductive graphene nanoplatelets (GNPs), are fabricated by a facile vacuum-assisted self-assembly method. The films exhibit the highest through-plane k value (9.09 Wm−1K−1) among reported polymer-based paper-like composites, excellent flexibility (in over 20,000 bending cycles) and robust mechanical properties (tensile strength ~10.6 MPa and elongation at break ~7.6%). The outstanding heat management capability of the fabricated films is demonstrated by demonstrative experiments and finite volume simulation, clearly showing the great potential to be used as super TIMs in advanced electronic packaging technology.

Forming a segregated conductive filler network at polymer particle interfaces enables the fabrication of high-performance conductive polymer composites at low filler content. However, this method is not applicable to thermosets that are not melt processable. Here, we report a facile and effective strategy to build a segregated filler network at epoxy waste particles and convert the system into a high-performance conductive composite. First, the permanent network in the epoxy waste is converted into a dynamic one via catalyst infusion. Subsequently, using an interface design strategy, branched carbon nanotubes (CNS) are introduced in the recycled epoxy system to form a segregated structure at the epoxy particle interfaces by compression molding. The resultant composites have excellent tensile properties, very low electrical percolation threshold and high electrical conductivity at low filler loading. This strategy enables the recycling of epoxy waste for the fabrication of high-performance composites for strain sensing and EMI shielding.

In this work, polyethylene (PE)/silica microsphere composite melt is used to penetrate the ethylene-α-octene block copolymer (OBC) melt in multi-melt multi-injection molding (M3IM) process. Due to the viscosity difference between PE/silica composite melt and OBC melt, a disturbed flow interface of these two melts formed. Thanks to the “shear-induced migration” theory in suspended balance model (SB model) and the unique flow field in M3IM, silica microspheres can be designed to migrate from high shear rate layer to low shear rate layer in PE/silica core melt, further to intaglio micro-pits on the interface of PE/silica core and OBC skin melt. As a result, the migrated silica microspheres can be intuitively observed by peeling off the OBC layer, as well as a “lotus seedpod”-like structure consisting of quantity-adjustable asperities and micro-pits can be constructed on the peeled surface of OBC layer. This work sheds lights to rapidly fabricate multi-tier structures by polymer melt processing strategies, aiming to manufacture functional devices on a large scale.

Superhydrophilic materials have attracted extensive attention as promising candidates for effective oil/water separation and water purification, however, realizing environmentally friendly and multifunctional materials with superhydrophilicity and underwater superoleophobicity is still a great challenge and urgently desired. In this work, we develop a controllable approach to achieve the superhydrophilicity of biodegradable electrospun stereocomplex polylactide (sc-PLA) membranes via the titanium carboxylate coordination bonding of gallic acid (GA) and tetrabutyl titanate (Ti(OBu)4) in aqueous solution, i.e. GA-modified TiO2 (GA-TiO2) coating. The GA-TiO2 coated sc-PLA (GT-sc) membranes show superhydrophilicity and underwater superoleophobicity in various harsh working conditions including corrosive organic solvents, saturated NaCl solution and acid solution at pH = 1, exhibiting effective and efficient separation property for a wide range of oil/water mixtures and oil-in-water emulsions. The GT-sc membranes can remove water-soluble contaminants such as methylene blue driven by gravity, leading to multifunctional water purification. Moreover, the GT-sc membranes possess splendid antifouling and self-cleaning performance resulting from the photocatalytic property of TiO2 under UV irradiation. Thus, this work provides an easily controlled route for fabricating green and durable membranes for multifunctional oil/water separation.

Simultaneously achieving high piezoresistive sensitivity, stretchability, and good electrical conductivity in conductive elastomer composites (CECs) with carbon nanofillers is crucial for stretchable strain sensor and electrode applications. Here, we report a facile and environmentally friendly strategy to realize these three goals at once by using branched carbon nanotubes, also known as the carbon nanostructure (CNS). Inspired by the brick-wall structure, a robust segregated conductive network of a CNS is formed in the thermoplastic polyurethane (TPU) matrix at a very low filler fraction, which renders the composite very good electrical, mechanical, and piezoresistive properties. An extremely low percolation threshold of 0.06 wt %, currently the lowest for TPU-based CECs, is achieved via this strategy. Meanwhile, the electrical conductivity is up to 1 and 40 S/m for the composites with 0.7 and 4 wt % CNS, respectively. Tunable piezoresistive sensitivity dependent on CNS content is obtained, and the composite with 0.7 wt % filler has a gauge factor up to 6861 at strain ε = 660% (elongation at break is 950%). In addition, this strategy also renders the composites' attractive tensile modulus. The composite with 3 wt % CNS shows 450% improvement in Young's modulus versus neat TPU. This work introduces a facile strategy to fabricate highly stretchable strain sensors by designing CNS network structures, advancing understanding of the effects of polymer-filler interfaces on the mechanical and electrical property enhancements for polymer nanocomposites.

Flexible pressure sensing applications such as prosthetic limbs and wearable electronics will benefit from pressure sensors with increased capacitive sensitivity. Therefore, to fabricate pressure sensors with increased sensitivity, hybrid composites of a new type of carbon nanofiller, carbon nanostructures (CNS, i.e. branched carbon nanotubes) and graphene nanoplatelets (GNP) at various compositions were mixed with thermoplastic polyurethane (TPU) to tune the composite dielectric properties. Furthermore, in congruence with the global effort towards less wasteful electronic device production, these capacitive sensors were fabricated in a facile and environment-friendly strategy. In a composition of CNS and GNP at a mass ratio of 3:1, the composite sensor shows the highest pressure sensitivity of 2.05 MPa−1 for 0–1.2 MPa pressure, compared with 0.18 MPa−1 for neat TPU, enabling potential wearable pressure sensor applications. The improved performance arises from the combination of interconnected CNS along with the high dielectric constant and suppressed loss of GNP.

Conductive polymer nanocomposites (CPNCs) have emerged as potential alternatives for metallic foil sensors and semiconductor strain gauges. The simultaneous achievement of high piezoresistive sensitivity and large strain ranges for CPNCs currently presents a great challenge and solving this challenge may extend the applications of CPNCs with self-diagnosis capabilities to many structural health-monitoring (SHM) systems. This paper reports a facile strategy for fabricating highly piezoresistive and tough poly(vinylidene fluoride) (PVDF) based CPNCs by tuning the interactions between the polymer matrix and multiwalled carbon nanotubes (CNT) using an ionic liquid (IL) as an interface linker/modifier. As a result, the presence of IL achieves homogeneous dispersion of CNTs in PVDF but causes a reduced number of CNT-CNT ohmic contacts with higher electrical contact resistance. According to the lower initial resistivity, piezoresistive sensitivity is greatly improved, and the gauge factor (GF) varies from 7 to 60 upon the addition of IL. It is also shown that IL tunes PVDF-CNT interfacial bonding and, as an effective interface linker/modifier, achieves significantly improved sensing strain ranges (increased from ca. 6 to 21%) and toughness (elongation at break increases from 6 to 130%) of CPNCs. These results substantially advance the understanding of the missing relationship between polymer-filler interface interactions and piezoresistive properties and have important implications for future studies of tuning polymer-filler interface bonding properties and piezoresistive sensitivity.

The surface damage processes of fused silica are studied by a new photo-acoustic probe with Anti-Emi (Electron-Magnetic Interference), easy-adjusted and non-damage for the samples, and the damage thresholds is detected according to the rapid increase of the acoustic signals. Experimental results show that the damage threshold of fused silica samples is 13.86 J/cm2 at the wavelength of 1064 nm and the pulse width of 10 ns. This work may provide an effective technical support for the laser-induced damage detection.

Flexible and highly sensitive pressure sensors have versatile biomedical engineering applications for disease diagnosis and healthcare. The fabrication of such sensors based on porous structure composites usually requires complex, costly, and nonenvironmentally friendly procedures. As such, it is highly desired to develop facile, economical, and environment-friendly fabrication strategies for highly sensitive lightweight pressure sensors. Herein, a novel design strategy is reported to fabricate porous composite pressure sensors via a simple heat molding of conductive fillers and thermoplastic polyurethane (TPU) powders together with commercially available popcorn salts followed by water-assisted salt removal. The obtained TPU/carbon nanostructure (CNS) foam sensors have a linear resistance response up to 60% compressive strain with a gauge factor (GF ) of 1.5 and show reversible and reproducible piezoresistive properties due to the robust electrically conductive pathways formed on the foam struts. Such foam sensors can be potentially utilized for guiding squatting exercises and respiration rate monitoring in daily physical training.

Piezoresistive poly(vinylidene fluoride) (PVDF) nanocomposites are very intriguing for strain sensor applications in structural health monitoring (SHM) systems. In general, high piezoresistive sensitivity combined with broad measurable strain ranges are greatly favored in those sensors. Here, a facile strategy, i.e. constructing strain susceptible conductive networks using hybrid filler systems consisting of carbon nanotubes (CNTs, 0.5-1 wt %) and carbon black (CB, 0.5-4 wt %), was introduced to tune both electrical conductivity and piezoresistive sensitivity of melt mixed PVDF nanocomposites. At the same filler content CNTs, due to their larger aspect ratio, contribute more to electrical conductivity improvements of nanocomposites than CB, while contacts between CB particles are more sensitive to tensile strain. With retained ductility of PVDF, tunable electrical conductivity and ΔR/R0-strain sensitivity can be achieved by combining the advantages of CNTs and CB by adjusting the conductive network structure. Conductivity improvement is more remarkable if the mass ratio of CNTs to CB (mCNTs/mCB), varied between 1:1 and 1:4, is higher in hybrid filler compositions. Lower mCNTs/mCB ratios result in higher ΔR/R0 values in PVDF nanocomposites whether they have the same content of total filler or similar/the same initial electrical resistivity. At 10% tensile strain, the highest ΔR/R0 of 0.65 was obtained for the nanocomposite filled with 0.5 wt % CNTs and 0.5 wt % CB, while that for the counterpart containing 1 wt % CNTs is 0.35 at the same strain. The concept of using hybrid fillers provides a low-cost and effective way to fabricate piezoresistive polymer nanocomposites toward SHM applications.