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Controlled generation of reactive oxygen species (ROS) is essential in biological, chemical, and environmental fields, and piezoelectric catalysis is an emerging method to generate ROS, especially in sonodynamic therapy due to its high tissue penetrability, directed orientation, and ability to trigger in situ ROS generation. However, due to the low piezoelectric coefficient, and environmental safety and chemical stability concerns of current piezoelectric ROS catalysts, novel piezoelectric materials are urgently needed. Here, we demonstrate a method to induce polarization of inert poly(tetrafluoroethylene) (PTFE) particles ( ~ 1–5 μm) into piezoelectric electrets with a mild and convenient ultrasound process. Continued ultrasonic irradiation of the PTFE electrets generates ROS including hydroxyl radicals (•OH), superoxide (•O 2 − ) and singlet oxygen (1 O 2 ) at rates significantly faster than previously reported piezoelectric catalysts. In summary, ultrasonic activation of inert PTFE particles is a simple method to induce permanent PTFE polarization and to piezocatalytically generate aqueous ROS that is desirable in a wide-range of applications from environmental pollution control to biomedical therapy. Controlled generation of reactive oxygen species (ROS) is essential in biological, chemical, and environmental fields. Here, the authors report that ultrasonication can induce polarization of inert poly(tetrafluoroethylene) to a piezoelectric electret and drive piezocatalytic generation of aqueous ROS.

In the present work an experimental investigation has been carried out to study the corona characteristics of a portable high voltage dc to dc booster device proposed and used by us for the first time as an innovation in corona charging of electrets. The experiments were conducted in a point-to-plane system to measure the corona current I as a function of applied corona voltage V and inter-electrode separation. Obtained results have been analyzed and discussed successfully in the light of cited works and show that both positive and negative corona produced by this device is consistent with the Townsend Relation adapted for point-to-plane geometry. This device is suitable and effective in applications where the local corona is required.

Polymer electrets are increasingly getting application in a very wide range. However, its charge trapped mechanism is still poorly understood. It is always challenging how to improve its charge trapped ability and to enhance its performance stability. In this study, a charge trapped mechanism, quasi-dipole model, is proposed for semi-crystalline polymer electrets. Every grain of crystallite is viewed as a dipole based on the polarisation effect between crystalline and amorphous region when charged. The energy level of the charge trap has a dependence on the crystallite structure. The more regular the crystallite grain structure the better charge stability is. The melt-blown polypropylene (MBPP) electret fabrics with α or mesomorphic crystallite are used as the model material to verify the rationality of the mechanism. The experiment results from thermally stimulating discharge and X-ray diffraction proved that the charge-trapped stability could be improved by means of transformation from meso-crystalline to α crystalline structure. The MBPP fabric containing α-crystallite shows much better charge trapped performance than one containing mesomorphic-crystallite because of more regular structure in α crystallite. The findings not only present new insight into charge-trapped phenomena in polymer electrets, but also provide innovation for the processing technology of polymer electret materials.

Electrets are dielectric materials that have a quasi-permanent dipole polarization. A single-molecule electret is a long-sought-after nanoscale component because it can lead to miniaturized non-volatile memory storage devices. The signature of a single-molecule electret is the switching between two electric dipole states by an external electric field. The existence of these electrets has remained controversial because of the poor electric dipole stability in single molecules. Here we report the observation of a gate-controlled switching between two electronic states in Gd@C82. The encapsulated Gd atom forms a charged centre that sets up two single-electron transport channels. A gate voltage of ±11 V (corresponding to a coercive field of ~50 mV Å–1) switches the system between the two transport channels with a ferroelectricity-like hysteresis loop. Using density functional theory, we assign the two states to two different permanent electrical dipole orientations generated from the Gd atom being trapped at two different sites inside the C82 cage. The two dipole states are separated by a transition energy barrier of 11 meV. The conductance switching is then attributed to the electric-field-driven reorientation of the individual dipole, as the coercive field provides the necessary energy to overcome the transition barrier.A Gd@C82 molecule shows electric polarization switching behaviour under a gate bias voltage, thus demonstrating a single-molecule electret device.

In recent years, the demand for sustainable and degradable materials and electronic devices has increased significantly. Among a range of biodegradable polymers, poly(lactic acid) (PLA) is a good alternative to conventional petrol-based polymers because of its attractive mechanical properties and its easy processability. Recently, PLA has also been described as a promising dielectric material with piezoelectric and electret properties. We expect that PLA—after further optimization—will play an important role as a material for environmentally friendly sensors in the future, where first applications such as air filters and pressure sensors have already been proposed. However, degradation under normal ambient conditions is very slow, and an accelerated and controllable degradation process is highly desirable for any type of PLA-based sensors. Enzymatic hydrolysis with embedded enzymes has been proposed as an approach to accelerate and control degradation. In this work, we investigate the properties of PLA in terms of dielectric and mechanical properties with a focus on its ability to store charges after the enzyme proteinase K (Trit. album) has been incorporated. Results reveal that proteinase K has a positive effect on the charge stability of solvent-cast PLA electrets after complete evaporation of the solvent. Furthermore, we observed a concentration-dependent acceleration of mass loss in a Tris-HCl buffer. A fast degradation within only one day occurred at a concentration of 6 wt% proteinase K.

Recently, electrical stimulation, as a non-pharmacological physical stimulus, has been widely exploited in biomedical and clinical applications due to its ability to significantly enhance cell proliferation and differentiation. As a kind of dielectric material with permanent polarization characteristics, electrets have demonstrated tremendous potential in this field owing to their merits of low cost, stable performance, and excellent biocompatibility. This review provides a comprehensive summary of the recent advances in electrets and their biomedical applications. We first provide a brief introduction to the development of electrets, as well as typical materials and fabrication methods. Subsequently, we systematically describe the recent advances of electrets in biomedical applications, including bone regeneration, wound healing, nerve regeneration, drug delivery, and wearable electronics. Finally, the present challenges and opportunities have also been discussed in this emerging field. This review is anticipated to provide state-of-the-art insights on the electrical stimulation-related applications of electrets.

We have developed a micro-electro-mechanical systems (MEMS) electrostatic vibratory power generator with over 100 μ W RMS of (root-mean-square) output electric power under 0.03 G RMS (G: the acceleration of gravity) accelerations. The device is made of a silicon-on-insulator (SOI) wafer and is fabricated by silicon micromachining technology. An electret built-in potential is given to the device by electrothermal polarization in silicon oxide using potassium ions. The force factor, which is defined by a proportional coefficient of the output current with respect to the vibration velocity, is 2.34 × 10 − 4 C/m; this large value allows the developed vibration power generator to have a very high power efficiency of 80.7%. We have also demonstrated a charging experiment by using an environmental acceleration waveform with an average amplitude of about 0.03 G RMS taken at a viaduct of a highway, and we obtained 4.8 mJ of electric energy stored in a 44 μ F capacitor in 90 min.

Recent research interest in organic field‐effect transistor (FET) memory has shifted to the functionality of photoprogramming in terms of its potential uses in multibit data storage and light‐assisted encryption and its low‐energy consumption and broad response to various optical bands. Phototransistor memory can be modulated through both electrical stress and light illumination, allowing it to function as an orthogonal operation method without mutual interference. Herein, the basic design concepts, requirements, and architectures of phototransistor memory are introduced. Design architectures such as channel‐only, channel‐with‐photogate, photochromatic channel devices and floating gate, photoactive polymer, and organic molecule‐based electrets are systematically categorized. The operational mechanism and impact of effective combinations of channels and electrets are reviewed to provide a fundamental understanding of photoprogramming as well as its potential future developmental applications as nonvolatile memory. Furthermore, recent advances in phototransistors and their diverse applications, including nonvolatile memory, artificial synapses, and photodetectors, are summarized. Finally, the outlook for the future development of phototransistors is briefly discussed. A comprehensive picture of the recent progress in phototransistors is provided. Herein, the basic design concepts and architectures of phototransistors are introduced. Design strategies involving channel‐only and channel‐with‐photogate devices as well as devices using floating gate, photoactive polymer, and organic molecule electrets are systematically categorized. Recent advances in phototransistors and their diverse applications: nonvolatile memory, artificial synapses, and photodetectors, are summarized. This review sheds light on the future development of phototransistors.

Polyvinylidene fluoride (PVDF) is a common semicrystalline fluoropolymer polymer. Due to its excellent piezoelectric properties, thermal stability, and mechanical strength, it has excellent processability and chemical tolerance to a range of materials such as acids, bases, organic solvents, grease, and fat. The current research provides an overview of recent advancements and developments in the implementation and modification of PVDF membranes, with a particular emphasis on sensors, biomedical engineering and devices, nanotechnology, solar applications, energy harvesting, and drug delivery carrier. Ferroelectric polymers are interesting from an electrical perspective. Ferroelectric polymers are insulating and polar and have a non-conjugated backbone, so they are known as strongly insulating materials from an optical perspective. Insulating polymers are particularly appealing for the study of charge transportation and storage. Because of their insulating properties and high concentration, such polymers often provide the best electrets for practical use. On the other hand, PMMA is an amorphous polymer, and poly (methyl methacrylate) (PMMA) advances have opened a wide variety of uses in nanotechnology. The understanding of PMMA properties has greatly aided recent advancements in the polymer’s synthesis, modification, and applications. As a result, this analysis aims to compare the physical, chemical, thermal, and mechanical properties of PVDF and PMMA. This article also gives a wise guide in the advancement of these two polymers in various fields of science and technology.

Non-uniform deformation of the dielectric subjected to external forces can induce the flexoelectric effect, a phenomenon that couples electrical polarization to strain gradients. However, limited by the size effects, flexoelectricity is not significant at the macroscale and only becomes catchable at the microscale and nanoscale. In recent work, we obtained a considerable flexoelectric-like response by crumpling the dielectric embedded with charges, i.e., the electret, which significantly improved the flexoelectric effect at the macroscale. In this work, we further optimize the macroscopic performance of the flexoelectric response by applying gradient treatment to the electret films. Specifically, we analytically derive the electromechanical coupling of crumpled electret films with gradients of different thicknesses, charge densities, and Young’s moduli as key design variables. It is shown that the gradient-oriented electret film can be tuned to nearly five times that of a uniform electret film.