A high-efficiency bio-based P/N synergistic flame retardant (PVFD) is synthesized by combining furfurylamine and vanillin. The compound incorporates two different valence states of phosphorus as flame retardant structures, namely phenylphosphoryl dichloride (PPDC) and 9,10-dihydro-9-oxa-10- phosphophenyl-10-oxide (DOPO). PVFD and epoxy resin (EP) can cure into a cross-linked network, thus not only improving the mechanical properties of EP but also achieving P/N synergistic flame retardant effects. Experimental results demonstrate that EP/PVFD-5 obtained by adding 5 wt% of PVFD to EP passes the UL-94 test and achieves V-0 grade, whose limiting oxygen index (LOI) is up to 38.0%. EP/PVFD-5 exhibits a decrease of 10.14% in peak heat release rate (PHRR), 16.90% in total heat release (THR), and 10.0% in total smoke release (TSP), while the residual carbon content increases by 8.5%. Additionally, the bending strength, bending modulus, tensile strength, and elongation at break of EP/PVFD-5 increase by 3.9%, 4.9%, 45.1%, and 26.3%, respectively.Highlights The bio-based raw materials we used are eco-friendly and readily available. PVFD, an efficient P-N synergistic compound, was synthesized. PVFD promotes the char formation of EP and dilutes the O2 concentration. PVFD does not cause the degradation of mechanical properties of EP. By combining furfurylamine and vanillin, a highly efficient bio-based P/N synergistic flame retardant (PVFD) was synthesized, which can participate in the curing of epoxy resin to form a good cross-linking system, and exert a good flame retardant effect with the synergistic effect of the condensed phase and the gas phase. image

A reactive flame retardant containing biphenyl structure (DEU-2DOPO) was prepared from the bio-based raw material eugenol. The incorporation of DEU-2DOPO into the epoxy resin serves to enhance the ring-opening reaction of the epoxy. Furthermore, the inclusion of DEU-2DOPO has been found to have a positive impact on the glass transition temperature and residual carbon rate of the epoxy resin. This additive also significantly improves the mechanical properties of the epoxy resin, leading to a 49.3% increase in tensile strength, an 81.9% increase in breaking elongation, and a 15.8% increase in flexural strength. Notably, when DEU-2DOPO is introduced at a concentration of 5 wt%, it not only achieves a V-0 rating in the UL-94 test but also exhibits an impressive ultimate oxygen index of 34.5%. Additionally, the cone calorimetric testing revealed that the presence of DEU-2DOPO results in lower combustion metrics compared to pure epoxy, as evidenced by a reduction of 15.1% in total heat release (THR) and 10.8% in total smoke release (TSR). An analysis of the flame retardant mechanism elucidates that DEU-2DOPO promotes the formation of a stable and dense residual carbon, thereby impeding gas and heat exchange. Furthermore, the decomposition of DEU-2DOPO generates PO· and PO 2 · radicals, which effectively neutralize reactive radicals.

Flexoelectricity is an electromechanical coupling effect in which electric polarization is generated by a strain gradient. In this investigation, a potassium sodium niobite/poly(vinylidene fluoride-trifluoroethylene) (KNN/PVDF-TrFE)-based nanocomposite is fabricated, and the flexoelectric effect is used to enhance the photovoltaic current (I pv) in the nanocomposite. It is found that both a pyroelectric current and photovoltaic current can be generated simultaneously in a light illumination process. However, the photovoltaic current (I pv) in this process contributes ≈85% of the total current. When assessing the effect of flexoelectricity with a curvature of 1/20, the I pv of the curved KNN/PVDF-TrFE (20%) (K/P-20) composite increased by ≈13.9% compared to that of the flat K/P-20 nanocomposite. Similarly, at a curvature of 1/20, the I pv of the K/P-20 nanocomposite is 71.6% higher than that of the PVDF-TrFE film. However, the photovoltaic effect induced by flexoelectricity is much higher than the increased polarization from flexoelectricity, so this effect is called as the flexophotovoltaic effect. Furthermore, the calculated energy conversion efficiency of the K/P-20 film is 0.017%, which is comparable to the previous research result. This investigation shows great promise for PVDF-based nanocomposites in ferroelectric memory device applications.

Electromechanical sensors play a large role in the development of artificial intelligence and the Internet of Things. In previous studies, it was found that monocharged electret nanogenerator (MENG)-based sensors exhibited a much-improved sensitivity and output performance compared to metallized electret-based devices. However, theoretical studies on MENG sensors are still lacking. This investigation is the first attempt at establishing a systematic theoretical model for MENG devices. The derived equations indicated that the output voltage of the device was proportional to the applied pressure, and that the sensitivity of the MENG device was only dependent on the device structure and charge density on the electret material. Furthermore, a fabricated MENG device demonstrated that its output voltage of the MENG device was proportional to the applied pressure and remained constant in a low frequency range. Moreover, both the sensitivity and current density of the device decreased with increasing l1. For a real device, I-sc of the device reached a maximum value at an l2 of 0.3mm and then started to decrease. Due to their advantageous flexibility, high sensitivity, and ease of fabrication, MENG devices show great promise for wearable devices and energy harvesting applications.

In the past few decades, ceramic/polymer nanocomposites have been extensively studied due to their relatively large dielectric constant, high electric energy density, and large charge–discharge efficiency. Antiferroelectric (AFE) materials possess a low remnant polarization (Pr) and relatively high saturation polarization (Ps), which can induce higher storage energy density than relaxor ferroelectric materials. In this investigation, AgNbO3-based AFE ceramic nanoparticles were grafted with a layer of poly(methyl methacrylate) (PMMA) to form AgNbO3–g-PMMA nanoparticles and then the obtained nanoparticles were embedded into a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix to form an AgNbO3–g-PMMA/PVDF-HFP (AN–g-PMMA/HFP) nanocomposite film. After characterization, it was found that the dielectric constant of the AN–g-PMMA/HFP-5 (5% AgNbO3) nanocomposite film was 12.3, which was 43% higher than that of the pristine PVDF-HFP film. The AN–g-PMMA/HFP-5 nanocomposite film exhibited the largest breakdown field of 500 MV m−1 and the highest energy density of 13 J cm−3, which was increased by 32.5% (from 9.82 to 13 J cm−3), as compared with that of the pristine PVDF-HFP film. The AN–g-PMMA/HFP-5 film exhibited a charge–discharge efficiency of 69.5% at 500 MV m−1, which is 9.5% higher than that of the pristine PVDF-HFP film. This AgNbO3-based nanocomposite film shows great promise for AFE nanocomposite for high energy density capacitor applications.

In addition to the rapid urbanization and industrialization around the world, air pollution due to particulate matter is a substantial threat to human health. A considerable research effort has been devoted to the development of electrospun polymer nanofibers for air filter applications. Among these new technologies, electrostatic charge-assisted air filtration is a promising technology for removing small particulate matter (PM). In this investigation, biodegradable electrospun poly(l-lactic acid) (PLLA) polymer nanofibers are employed for air filter applications. Electrostatic charges generated from the PLLA nanofiber can significantly enhance air filter applications. Compared with a 3M commercial respirator filter, electrospun PLLA fibrous filters exhibit a high efficiency of 99.3%. Even after 6 h of filtration time, the PLLA filtration membrane still exhibits a 15% improvement in quality factor for PM 2.5 particles than the 3M respirator. This is mainly attributed to the electrostatic force generated from the electrospun PLLA nanofibers, which significantly benefit submicron particle absorption. Due to their biodegradability, ease of fabrication, and relatively high efficiency, electrospun PLLA nanofibers show great promise in applications such as air cleaning systems and personal air purifier applications.

With the rapid development of the internet of things, sensors play an increasingly critical role in the measurement of force, temperature, and light. In article number 1807618, Kailiang Ren, Zhong Lin Wang, and co-workers propose a self-powered pressure sensor based on an electret nanogenerator. This device holds great promise for use in future tactile sensors and artificial skin applications.

This study reports a self‐powered pressure sensor based on a monocharged electret nanogenerator (MENG). The sensor exhibits great advantages in terms of high reliability, ease of fabrication, and relatively high sensitivity. The working mechanism of the MENG sensor is studied by both theoretical derivations and finite element analyses to determine the electric potential distribution during the device operation. The MENG sensor exhibits a stable open circuit voltage ≈10 V at a 30.8 kPa pressure and a corresponding sensitivity of 325 mV kPa−1. The stability testing result shows that the device has only ≈5% attenuation after 10 000 cycles of repeated testing at 30.8 kPa pressure. Furthermore, it is found that the MENG sensor responds not only to a dynamic force but also a static force. Finally, a sensor array consisting of nine MENG sensor elements is fabricated. The testing results from the sensor array also reveal that a single touch of the sensor element can immediately light up an LED light at the corresponding position. This device holds great promise for use in future tactile sensors and artificial skin applications.

Polytetrafluoroethylene (PTFE)‐based electret materials have emerged as one of the most widely used materials in underwater transducer, microphone, and transistor applications. In this paper, it is shown for the first time that a monocharged (single type, electron) PTFE electret material can be used in energy harvesting and self‐powered device applications, such as wristband and shoe insole devices. At first, a theory based on the electrostatic effect is derived for the first time for monocharged electret generator (MCEG). For a hand‐shaking movement, the MCEG‐based wristband device can generate an output voltage and current of 14 V and 0.65 µA, respectively. Furthermore, it is found that the MCEG‐based shoe insole device can generate a maximum output voltage of 178 V and a current of 2.85 µA during walking. The maximum harvested power obtained is ≈35.63 µW in shoe insole‐based devices under a resistor load. Additionally, the power generated from the shoe insole device can light up 55 light‐emitting diodes with a single step of walking. Because of the relatively large output power density, ease of fabrication, and chemical stability, this device shows great promise for wearable self‐powered device applications.

Organic/inorganic nanocomposite materials have been extensively studied for high energy density capacitor applications due to their relatively large dielectric constant. However, most of these nanocomposite materials suffer from a very low breakdown field. In this investigation, poly(methyl methacrylate) (PMMA) grafted titanium dioxide (TiO2) (TiO2-g-PMMA) was synthesized through a seeded emulsion polymerization method. Then, the hybrid nanoparticles were incorporated into a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) film using solution casting to form a PVDF-HFP/TiO2-g-PMMA nanocomposite. After the characterization, it was revealed that the TiO2 nanoparticles were perfectly coated with the PMMA layer. Furthermore, the dielectric measurement results showed that the permittivity nanocomposite was enhanced by 13.9% as compared with the pristine PVDF-HFP film. The polarization loop data of the nanocomposite indicated that the highest breakdown field and energy density of the PVDF-HFP film with 1 vol. % TiO2-g-PMMA reached 560 MV/m and 14.2 J/cm3, respectively. The breakdown field of the nanocomposite with grafting is doubled as compared with the nanocomposite without grafting. Furthermore, as compared with the pristine PVDF-HFP at the same electric field, the energy density of the PVDF-HFP/TiO2-g-PMMA nanocomposite (1 vol. %) is increased by 14.4% (from 12.4 to 14.2 J/cm3). The nanocomposite film also showed an improved charge-discharge energy efficiency of 47% under 500 MV/m electric field, which was much higher than the pristine PVDF-based polymer. The PVDF-HFP/TiO2-g-PMMA nanocomposite shows a great promise for future high energy density capacitor applications.

In this paper, we investigated the blend film of poly(vinylidene fluoride-trifluoroethylene)/poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-TrFE)/P(VDF-HFP)) with various compositions for high energy density applications. After characterization using x-ray diffraction and transmission electron microscopy, it was found that the crystallinity and spherulite size of the material decreased with the increasing PVDF-HFP contents in the blend film. Furthermore, the blend film showed a maximum breakdown field of 820 MV m-1 and an energy density of 23.8 J cm(-3) for the blend film with a 5: 5 composition ratio (P(VDF-TrFE)/P(VDF-HFP)). Moreover, the mechanisms of the breakdown field associated with the spherulite size and the crystallinity of the blend film were investigated for the first time. It was revealed that for the materials with similar Young's moduli, the breakdown field is greatly improved with the reduced spherulite size and decreased crystallinity of the P(VDF-TrFE)/P(VDF-HFP) blend film. This investigation shows an effective approach for improving the breakdown field of dielectric materials in high energy density capacitor applications.

Since the last decade, piezoelectric polymer nanofibers have been of great interest in the stimulation of cell growth and proliferation for tissue engineering and wound healing applications. To date, there is no clear understanding of how the piezoelectric properties of piezoelectric materials can be affected by electrospinning parameters and how the piezoelectricity from the electrospun polymer nanofibers produced under optimized electrospinning conditions in vivo would affect cell growth, proliferation and elongation. In this paper, it is shown for the first time how electrospinning parameters, such as solution concentration and collecting distance (from the needle to the rotating mandrel), can affect the piezoelectricity of the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibers. Here, the optimized electrospinning conditions for P(VDF-TrFE) nanofibers were achieved and these nanofiber scaffolds (NFSs) were used for implanted energy harvester in SD rats, cell proliferation and cell alignment growth applications. During the process of slightly pulling implanted site of SD rats, the implanted PVDF-TrFE NFSs generated a maximum voltage and current of 6 mV and similar to 6 nA, respectively. With great cytocompatibility and relatively large piezoelectric effect, fibroblast cells grew and aligned perfectly along the electrospinning direction of P(VDF-TrFE) nanofiber direction and cell proliferation rate was enhanced by 1.6 fold. Thus, electrospun P(VDF-TrFE) NFSs show great promise in tissue engineering and wound healing applications.

To facilitate the development of new polymeric materials, we report the development of new heuristic models to predict the dielectric constant, band gap, dielectric loss tangent, and glass transition temperatures for organic polymers. A new set of features called infinite chain descriptors (ICDs) was designed and developed especially to characterize organic polymers, utilizing methods with minimal dependence on pre-defined fragment libraries. Machine learning models were built for the aforementioned properties incorporating best practices in the field such as objective feature selection, cross-validation and external test sets. All models produced in this study showed good performance in prediction. A web tool has been developed and has been made available that supports the input of novel structures. (C) 2016 Wiley Periodicals, Inc.

Being in the group with the most diverse set of properties among all in the periodic table, the Group 14 elements (C, Si, Ge, Sn, and Pb) are particularly interesting candidates for structure–property investigation. Motivated by the need to create new insulators for energy storage and electronics applications, we study a few compounds based on Group 14 elements in this work, namely the dihydrides, dichlorides, and difluorides. Using density functional theory (DFT) calculations, we establish patterns in their properties, including favored coordination chemistry, stability, electronic structure, and dielectric behavior. While a coordination number (CN) of 4 is commonly associated with Group 14 elements, there is a significant deviation from it down the group, with CNs as high as 7 and 8 common in Pb. Further, there is an increase in the relative stability of the +2 oxidation state as opposed to +4 when we go from C to Pb, a direct consequence of which is the existence of the di-compounds of C and Si as polymers, whereas the compounds of Ge, Sn, and Pb are strictly 3D crystalline solids. The coordination chemistries are further linked with the band gaps and dielectric constants (divided into two components: the electronic part and the ionic part) of these compounds. We also see that the more stable difluorides and dichlorides have large band gaps and small electronic dielectric constants, and most of the Ge and Sn compounds have remarkably large ionic dielectric constants by virtue of having polar and more flexible bonds. The staggering variation in properties displayed by these parent compounds offers opportunities for designing derivative materials with a desired combination of properties.

Chemical defects in polyethylene (PE) can deleteriously downgrade its electrical properties and performance. Although these defects usually leave spectroscopic signatures in terms of characteristic luminescence peaks, it is nontrivial to make unambiguous assignments of the peaks to specific defect types. In this work, we go beyond traditional density functional theory calculations to determine intra-defect state transition and charge recombination process derived emission and absorption energies in PE. By calculating the total energy differences of the neutral defect at excited and ground states, the emission energies from intra-defect state transition are obtained, reasonably explaining the photoluminescence peaks in PE. In order to study the luminescence emitted in charge recombination processes, we characterize PE defect levels in terms of thermodynamic and optical charge transition levels that involve total energy calculations of neutral and charged defects. Calculations are performed at several levels of theory including those involving (semi)local and hybrid electron exchange-correlation functionals, and many-body perturbation theory. With these critical elements, the emission energies are computed and further used to clarify and confirm the origins of the observed electroluminescence and thermoluminescence peaks.

To date, trial and error strategies guided by intuition have dominated the identification of materials suitable for a specific application. We are entering a data-rich, modelling-driven era where such Edisonian approaches are gradually being replaced by rational strategies, which couple predictions from advanced computational screening with targeted experimental synthesis and validation. Here, consistent with this emerging paradigm, we propose a strategy of hierarchical modelling with successive downselection stages to accelerate the identification of polymer dielectrics that have the potential to surpass ‘standard’ materials for a given application. Successful synthesis and testing of some of the most promising identified polymers and the measured attractive dielectric properties (which are in quantitative agreement with predictions) strongly supports the proposed approach to material selection.

We use simulations and experiments to delineate the mechanism by which the addition of a small number of polar −OH groups to a nonpolar polymer increases the static relative permittivity (or dielectric constant) by a factor of 2, but more importantly while keeping the dielectric loss in the frequency regime of interest to power electronics to less than 1%. Dielectric properties obtained from experiments on functionalized polyethylenes and polypropylenes as a function of −OH doping are in quantitative agreement with one another. Molecular dynamics simulations for the static relative permittivity of “dry” −OH functionalized polyethylene (in the absence of water) are apparently in quantitative agreement with experiments. However, these simulation results would further imply that there should be considerable dielectric loss beyond simulation time scales (>0.1 μs). Since there are minimal experimentally observed dielectric losses for times as short as a microsecond, we believe that a small amount of adsorbed w...