Mechanism Of Electrification Research Articles

Research on trap characteristic mechanisms of thermochromic phase change epoxy composite with confined structure

Thermochromic phase change insulating composite can possess a series of advanced functions under electrothermal stimuli, which has been widely applied in a great number of intelligent electrical and electronic devices. However, due to the confined structure of thermochromic phase change insulating composite, the trap characteristics cannot be analyzed by existing interface models of nanodielectrics, which inhibits the scientific improvement of dielectric reliability under the electrothermal stress. In this paper, the trap characteristic and mechanism of thermochromic phase change epoxy composites are studied by the isothermal surface potential decay (ISPD) and the Kelvin probe force microscopy (KPFM). The results show that the variation trends of trap characteristics after introducing confined structures at 30 ℃ and 70 ℃ are opposite, which could derive from the confined phase change or the confined interface. Theoretical analysis shows that the influence of confined phase change on temperature dependent trap characteristics is inconsistent with experimental results, which cannot be the essential reason for affecting the trap characteristics. KPFM <i>in-situ</i> characterization directly verifies the existence of potential barriers in the confined interface, which originates from the contact electrification mechanism. The variation of temperature dependent charge quantity due to contact electrification at the confined interface can affect the barrier height, which can substantially affect the temperature dependent trap characteristics.

Thermal Performance of Nanofluid Flow Along an Isothermal Vertical Plate with Velocity, Thermal, and Concentration Slip Boundary Conditions Employing Buongiorno’s Revised Non-Homogeneous Model

This study examines the natural convection of a steady laminar nanofluid flow past an isothermal vertical plate with slip boundary conditions. A review of existing literature reveals no prior research that has explored the combined effects of thermophoresis, Brownian diffusion, and particle electrification while considering slip boundary conditions in nanofluid flow. Buongiorno’s revised four-equation non-homogeneous model, incorporating mechanisms for thermophoresis, Brownian diffusion and particle electrification, is utilized to address this gap. The model employs velocity, thermal, and concentration slip boundary conditions to investigate enhancing the nanofluid's thermal conductivity. The resulting local similar equations are tackled using MATLAB's bvp4c package. The study discusses the influence of key parameters, such as thermophoresis, Brownian motion, and electrification, on temperature, velocity, and concentration distributions, as well as on heat, mass transfer and skin friction coefficients. The findings of the simulation are consistent with previous studies, showing that an improvement in the electrification parameter rises the heat transfer coefficient, while thermophoresis and Brownian motion parameters have the opposite effect. Additionally, mass transfer coefficient values increase with higher Brownian motion and electrification parameters while reducing with the thermophoresis parameter. This physical model has potential applications in heat exchangers using nanofluids and in cooling plate-shaped products during manufacturing processes. The novelty of this study lies in the analysis of Brownian diffusion, thermophoresis, and particle electrification mechanisms in nanofluid flow under slip boundary conditions.

A Study on the Mechanisms and Performance of a Polyvinyl Alcohol-Based Nanogenerator Based on the Triboelectric Effect.

Polyvinyl alcohol (PVA), a versatile polymer, is extensively used across many industries, such as chemicals, food, healthcare, textiles, and packaging. However, research on applying PVA to triboelectric nanogenerators (TENGs) remains limited. Consequently, we chose PVA as the primary material to explore its contact electrification mechanisms at the molecular level, alongside materials like Polyethylene (PE), Polyvinylidene fluoride (PVDF), and Polytetrafluoroethylene (PTFE). Our findings show that PVA has the highest band gap, with the smallest band gap occurring between the HOMO of PVA and the LUMO of PTFE. During molecular contact, electron transfer primarily occurs in the outermost layers of the molecules, influenced by the functional groups of the polymers. The presence of fluorine atoms enhances the electron transfer between PVA and PTFE to maximum levels. Experimental validation confirmed that PVA and PTFE contact yields the highest triboelectric performance: VOC of 128 V, ISC of 2.83 µA, QSC of 82 nC, and an output power of 384 µW. Moreover, P-TENG, made of PVA and PTFE, was successfully applied in self-powered smart devices and monitored human respiration and bodily movements effectively. These findings offer valuable insights into using PVA in triboelectric nanogenerator technologies.

Electrostatic energy-driven contact electrification mechanism from the ReaxFF molecular dynamics perspective.

Understanding the underlying principles of contact electrification is critical for more efficient triboelectric nanogenerator (TENG) development. Herein, we use ReaxFF molecular dynamics simulations in conjunction with a charge equilibration method to investigate the contact electrification mechanism in polyisoprene (PI), a natural rubber polymer, when it comes into contact with copper (Cu) and polytetrafluoroethylene (PTFE). The simulations reveal that the charge transfer directions in the PI/Cu and PI/PTFE contact models are opposite, and the amount of charge transfer in the former is substantially less than that in the latter, which are consistent with our TENG measurements. Contact electrification is revealed to be a spontaneous process that occurs to lower electrostatic energy, and the electrostatic energy released during contact electrification of PI/PTFE is greater than that of PI/Cu, which can be correlated with the relative strength of triboelectric charging observed for the two systems. A compression simulation of the PI/Cu contact model reveals that the quantity of charge transfer grows exponentially as compressive strain increases. Despite increasing the total energy of the system due to densification and distortion of the polymer structure, the applied deformation results in an energetically more stable electrostatic arrangement. We also find that the incorporation of a carbonaceous material into a polyisoprene matrix causes a faster increase in the amount of charge transfer with compressive strain, which is governed by a steeper electrostatic energy profile. This study provides an alternative perspective on the contact electrification mechanism, which could be beneficial for the development of energy harvesting devices.

3D visualization microscope of TENG contact interface based on astigmatic imaging

The triboelectric nanogenerator (TENG) is a mechanical device that can collect mechanical energy from the contact and separation of different materials. Due to the short distance of charge transfer, the characterization of the micro-contact state under localized stress has become an urgent issue in the study of TENG’s contact electrification mechanism. Most of the contact surfaces of TENG are curved surfaces, and there is a lack of effective means to characterize the contact state of curved surfaces. In this article, a technique based on astigmatic imaging principle is provided to visualize the three-dimensional contact interface of TENG, using polydimethylsiloxane (PDMS) and butyronitrile film with rough surface as TENG. Through this technique, the three-dimensional deformation of its contact interface was observed and the three-dimensional effective contact area was calculated. The comparison of current density generated at different pressing pressures verified that larger contact area leads to higher current density, which applies to the law in 3D contact interfaces as well. Visualizing conformal contact interfaces for TENG provide a powerful tool for analyzing the charge transfer-contact separation phase coordination mechanism, providing a new route approaching larger output efficiency. In addition, this technology offers possibility for characterization of TENG with both-side deformable, which abandons the requirements of the rigid contact surface in the total reflection scheme and is much more applicable for organic TENG.

Explosive eruption style modulates volcanic electrification signals

Volcanic lightning detection has proven useful to volcano monitoring by providing information on eruption onset, source parameters, and ash cloud directions. However, little is known about the influence of changing eruptive styles on the generation of charge and electrical discharges inside the eruption column. The 2021 Tajogaite eruption (La Palma, Canary Islands) provided the rare opportunity to monitor variations in electrical activity continuously over several weeks using an electrostatic lightning detector. Here we show that throughout the eruption, silicate particle charging is the main electrification mechanism. Moreover, we find that the type of electrical activity is closely linked to the explosive eruption style. Fluctuations in the electrical discharge rates are likely controlled by variations in the mass eruption rate and/or changes in the eruption style. These findings hold promise for obtaining near real-time information on the dynamic evolution of explosive volcanic activity through electrostatic monitoring in the future.

Formation of the crust on the surface of cold-climate aeolian quartz grains – A nano-scale study

Sand-sized quartz grains selected from sediments of a Pleistocene inland dune (eastern Poland) were subjected to a series of laboratory analyses, including grain-size distribution, morphoscopy analysis, microtextural analysis using scanning electron microscope (SEM) and nanostructural analysis using transmission electron microscope (TEM). The results indicate the presence of a crust on the surface of all of the studied quartz grains and a surprisingly low number of aeolian-induced mechanical microtextures. The TEM examination identifies illite-smectite assemblages as the main component of the crust, accompanied by amorphous silica, local accumulation of Fe, K, Ca, Mg oxides, and mineral particles (quartz, K-feldspar, chlorite). The thickness of the crust reaches approx. 0.1–0.2 μm and varies from the minimum on micro-protrusions up to the maximum in micro-cavities. Here, we present a new theory on the origin of the crust observed on the surface of cold-climate aeolian quartz grains. We postulate that the crust is formed within a near-surface saltation layer during active aeolian transport of sand-sized grains and clay-sized particles operating under cold-climate conditions. The development of abrasion features and the formation of the crust are interpreted here to occur simultaneously and continuously during the aeolian transport. The formation of the crust results from specific properties of aeolian transport (i.e. self-induced electrification and electrification mechanisms of quartz grains) and the quartz grains themselves (i.e. grain shape and surface microtopography).

Heat and Mass Transport Aspects of Nanofluid Flow towards a Vertical Flat Surface influenced by Electrified Nanoparticles and Electric Reynolds Number

This study examines the heat and mass transfer aspects of the natural convective flow of a nanofluid along a vertical flat surface, incorporating electrified nanoparticles and electric Reynolds number. While conventional nanofluid models like Buongiorno’s model overlook the nanoparticle electrification and electric Reynolds number mechanisms, this study addresses the nanoparticle electrification and electric Reynolds number mechanisms by justifying its relevance, particularly when tribo-electrification results from Brownian motion. This incorporation of the electric Reynold number and nanoparticle electrification mechanism is a unique aspect of this investigation. Using the similarity method and nondimensionalization, the governing partial differential equations of the flow are transformed into a set of locally similar equations. MATLAB's bvp4c solver is employed to solve this set of equations, along with the boundary conditions. The obtained results are validated by comparison with those from previously published works. Graphical representations are provided for the numerical outcomes of non-dimensional velocity, concentration and temperature concerning the nanoparticle electrification parameter and electric Reynolds number. The combined effects of the nanoparticle electrification parameter and the electric Reynolds number on non-dimensional heat and mass transfer coefficients are examined in tabular form. Furthermore, the impact of the nanoparticle electrification parameter on both heat and mass transfer for varying values of the Brownian motion parameter is explored graphically. The primary finding of this investigation indicates that the electrification mechanism of nanoparticles quickens the transfer of heat and mass from a flat surface to nanofluid, suggesting promising prospects for utilization in cooling systems and biomedical applications.

A self-powered metamaterial augmented nanogenerator for low-frequency acoustic telecommunication

This study introduces a novel self-powered metamaterial augmented nanogenerator for low-frequency acoustic telecommunication (MANLAT), which is designed to enhance acoustic communication capabilities by utilizing the local resonance mechanism to selectively amplify specific frequency bands of incident sound and generate large amplitude signals in a self-powered manner. The MANLAT device consists of a flexible bottom that responds to pressure differences by generating strong vibrations. Additionally, a lightweight cone-shaped component is attached to the central part of the flexible plate, thus increasing the surface area in that region. Through contact electrification and electrostatic induction mechanisms, a substantial electrical signal is generated, allowing the device to serve as a self-powered acoustic telecommunication receiver. To assess its performance in real-world scenarios, environmental interference was simulated by generating white noise added to the modulated waveform containing information, which was then transmitted through a loudspeaker. At the receiving end, a high-precision microphone sensor was used alongside the MANLAT device to capture the sound wave. The experimental results demonstrate that the MANLAT device surpassed the microphone sensor in mitigating noise interference and enabled the effective decoding of information even in the presence of high levels of white noise or background music. Consequently, the device simplifies communication systems, facilitates reliable and environmentally friendly communication, and enhances information security.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications.

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Water-Assisted Contact Electrification Properties of Selected Polymers and Surface Functionalization Molecules: A Computational Study.

Motivated by the requirements of performance stability in environments of variable humidity, the focus of this study is on the effects and role of humidity-induced water molecules and ions in the contact electrification (CE) mechanisms of triboelectric materials. In particular, the compatibility of direct charge transfer-based CE and other generally known or proposed water molecules or OH/H3O ion-facilitated CE mechanisms was assessed for a set of high-performance polymeric materials and functionalization molecules. The first set of test mechanisms included OH/H3O ion adsorption at the low-humidity limit. The adsorption resulted in physisorption or H transfer involving reactions that were not fully compatible with charge affinity-driven CE reactions on the considered contact surfaces for both ions in terms of the potential increase of the resultant density of surface charge. An alternative mechanism, which yielded compatibility at a large humidity limit, consisted of free energy-driven segregation and separation of the ions. Further test mechanisms included water adsorption-induced charge transfer and two mechanisms pertinent to charged material transfer: adsorption modulation due to formation of water monolayers and water solvation-induced separation of polymer fragments. According to the obtained results, both mechanisms could be verified as viable contributors to enhanced charge transfer. Consequently, the results allowed for conclusions regarding the general applicability of different, water-assisted CE mechanisms and the selection of particular pairs of contact materials of similar type for optimum performance in humid environments.

Strategies to Improve the Output Performance of Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) can collect and convert random mechanical energy into electric energy, with remarkable advantages including broadly available materials, straightforward preparation, and multiple applications. Over the years, researchers have made substantial advancements in the theoretical and practical aspects of TENG. Nevertheless, the pivotal challenge in realizing full applications of TENG lies in ensuring that the generated output meets the specific application requirements. Consequently, substantial research is dedicated to exploring methods and mechanisms for enhancing the output performance of TENG devices. This review aims to comprehensively examine the influencing factors and corresponding improvement strategies of the output performance based on the contact electrification mechanism and operational principles that underlie TENG technology. This review primarily delves into five key areas of improvement: materials selection, surface modification, component adjustments, structural optimization, and electrode enhancements. These aspects are crucial in tailoring TENG devices to meet the desired performance metrics for various applications.

Electrification Mechanism and Influence Factors of Sliding Triboelectric Nanogenerators Based on Micro‐Contact Model

As a new green energy‐harvesting technology, the electrification mechanism and output performance of triboelectric nanogenerators (TENGs) have become the research focuses and difficulties. Based on the basic principles of contact and damage mechanics, a five‐stage micro‐contact model is proposed on the interface of sliding TENGs friction subsurface. Experimental bench is built to complete the experimental validation and factors affecting the output performance of TENGs are experimentally investigated. In the results, it is shown that the contact form of the asperities on the surface of the friction subsurface determines the real contact area and the form of energy conversion, and the dynamical processes between the asperities are influenced by the velocity, load, and material, which further affect the elastic/plastic change of the friction surface and the directional transfer of contact electrons. Normal loading promotes the density and efficiency of electron transfer between the interfaces of the friction sub‐interfaces, but the electrical output performance of the system is no longer enhanced when the load is too high (≥10 N). The faster sliding speed is conducive to improving the output performance of the horizontal sliding TENG in a certain range (0.005–0.100 m s−1).

Contact electrification controlled by material deformation-induced electronic structure changes

The effective control of triboelectricity through material development is crucial for the safety of electronics and human well-being. However, owing to the absence of fundamental research on the mechanism of triboelectricity, material development has stagnated in this regard. In this study, we investigated the deformation effect on triboelectric behavior to enable a comprehensive understanding of the contact electrification mechanism. Theoretical results demonstrated that deformation leads to a reduction in the energy level associated with electron-accepting properties, thereby enhancing the tribonegative behavior of tribonegative materials. Conversely, the energy level related to electron-donating properties decreases, resulting in a waning of the tribopositive behavior of tribopositive materials. The experimental results further demonstrated that, consistent with the theoretical results, increased deformation induces an enhancement in the output of tribonegative materials while decreasing the output of tribopositive materials. Our findings provide a fundamental basis for controlling triboelectricity and advancing the development of stagnant triboelectric materials.

Comparison of Contact Electrification Mechanisms of Selected Polymers and Surface-Functionalized Molecules.

Among the possible alternatives for the improvement of contact electrification for triboelectric energy harvesting purposes, the functionalization of contact surfaces has attracted wide attention due to its versatility and cost-efficiency. Similarly, low-stiffness polymeric materials such as poly(dimethylsiloxane) (PDMS) are regarded as a promising choice of contact material for the same purpose. However, for defining the most efficient combinations of materials of the aforementioned types, a number of theoretical questions still frequently pose difficulties for practical implementation-related tasks. In this regard, the presented study theoretically assesses the possibilities of consistently selecting optimum performance combinations of contact materials. Here, the optimum is defined as the minimum energy of the charge transfer reaction and, consequently, the maximum density of the predicted triboelectric surface charge. With this aim, the most promising combinations in terms of electron-transfer energies were identified among the candidates of functionalized molecules and polymers. Based on the ordering of materials according to the basic characteristics of charge-transfer reactions─electron and hole affinities─certain differences were observed. These findings indicate that for the materials under consideration, it is not possible to establish a single triboelectric series solely based on a single characteristic. Furthermore, to evaluate the potential compatibility of charge-transfer reaction mechanisms based on electron and material transfer, molecular dynamics simulations were conducted using structures that depict pairs of polymers and self-assembled monolayers of functionalized molecules in contact and separated types of operations. The obtained results indicate that the formation of equally charged free fragments of polymer chains is likely taking place in the contact electrification for N-(2-aminoethyl)-3-aminopropyl trimethoxysilane/PDMS interfaces. At variance, a contact electrification mechanism by charge-dependent material transfer may occur for 1H, 1H, 2H, 2H-perfluorooctyl trimethoxysilane/PDMS interfaces.

Electric field as extracellular enzyme activator promotes conversion of lignocellulose to humic acid in composting process

To promote efficient conversion of lignocellulose to humus (HS) during composting, a novel bio-electrochemical technology was applied and explored the effect and mechanism of electrification on carbon conversion during different composting periods. The results showed that supplementary electric field played different roles during composting. In the early stage, organic matter mineralization was significantly accelerated under electric field application, that was embodied in a 29.8% increase of CO2 emission due to the enhanced metabolic activity of microorganisms. However, the electric field functioned as an extracellular enzyme activator during the later stage since the abundance of functional microorganisms related to lignocellulose degradation was increased by 1.5–2.8 fold that effectively promoted the conversion of lignocellulose to HS. The humic acid content of the compost products increased by 23.0–32.9% compared with control. This study elucidated how electric fields affect carbon conversion during composting, which provides a novel strategy for returning agricultural wastes to soil.

Contact Electrification at Dielectric Polymer Interfaces: On Bond Scission, Material Transfer, and Electron Transfer

AbstractTriboelectric nanogenerators (TENGs) are revolutionizing mechanical‐to‐electrical energy harvesting. TENGs harvest energy through the polymer–polymer contact electrification (PCE) mechanism, driven by nanoscale processes at the contact interface. Currently, when discussing PCE there are two distinct schools of thought on which nanoscale interactions drive charging at the contact interface; 1) electron transfer, where orbital overlap leads to charge tunneling between polymers; or 2) mass (material) transfer, where polymer chain entanglement and intermolecular bonding leads to heterolytic bond scission. Here, a combination of in silico and benchtop experiments is used to elucidate the relative role of electron and mass transfer in PCE. In silico experiments show that covalent bond scission in a polymethylmethacrylate/polytetrafluoroethylene system occurs at 348 kcal mol−1, prior to electron cloud overlap, where the highest occupied molecular orbital and lowest unoccupied molecular orbital of the system remain separated by 163 kcal mol−1. Benchtop experiments show PCE‐generated charges cannot be simply discharged via electrical grounding, indicating the formation of bound surface charge from mass transfer. The calculations and contact‐electrification tests provide strong evidence to support mass transfer being the leading mechanism driving PCE.

Recent Progress in Flow Energy Harvesting and Sensing Based on Triboelectric Nanogenerators

AbstractTriboelectric nanogenerators (TENGs), as a novel energy harvesting technology, have attracted increasing attention. This review paper focuses on the application of TENGs in flow energy harvesting and self‐powered flow sensing systems, as well as the latest research progress in this field. First, the working principle of TENG is introduced in detail, including the electrification mechanism and four basic working modes. Subsequently, the common applications of TENG‐based flow energy harvesting are systematically classified and summarized. In addition, the designs and principles for harnessing wind energy, wave energy, water flow energy, and droplet energy are illustrated individually. Furthermore, the common applications of TENG in flow sensing are elucidated, involving flow velocity and direction, flow rate measurement, respiration monitoring, water level, and wave motion monitoring. Finally, the current challenges in this field, such as the stability of TENG performance, scalability and integration, environmental impact and durability, etc., are discussed and future research directions, such as developing new TENG materials and designing more high‐efficiency TENG structure, are proposed. It is hoped that this review paper can actively promote the research and application of TENGs and contribute to the development of this field.

Contact Electrification at Adhesive Interface: Boosting Charge Transfer for High‐Performance Triboelectric Nanogenerators

AbstractCharge transfer, a decisive feature for surface charge density in triboelectric nanogenerators (TENGs), differs in quantity and species at different contact interfaces. Regarded as the main electrification mechanism, electron transfer has been extensively investigated in constructing high‐performance tribo‐materials and TENGs, in which material transfer has been always neglected. Here, it is demonstrated that material transfer is a crucial electrification mechanism for adhesive polymers in contact electrification, and plays a dominant role in boosting charge transfer and TENG performance. Specifically, as a new strategy for utilizing the adhesion capability, this study introduces the stabilized poly(thioctic acid) adhesives as tribo‐materials to maximize contact electrification. With material transfer at the adhesive interface, abundant mechanoions are generated through covalent bond cleavage and higher charge density is obtained from the triboelectric pairs with larger interfacial adhesion force. Under a gentle triggering condition (5 N, 1 Hz), the TENG can achieve a high charge density of 14.65 nC∙cm−2, with a maximum output power density of 10 W∙m−2. Furthermore, the TENG exhibits unique frequency‐insensitive, pressure‐ and temperature‐enhanced output characteristics. This study provides new insight into constructing high‐performance TENGs using adhesives and highlights the indispensable role of material transfer in polymer contact electrification.

Triboelectric nanogenerators

By combining the effects of contact electrification and electrostatic induction, triboelectric nanogenerators (TENGs) can effectively convert mechanical energy into electric power or signals. Over the past decade, TENG development has progressed rapidly, from fundamental scientific understanding to advanced technologies and applications. This Primer gives a brief overview of TENGs, including the mechanisms of contact electrification and electrodynamics, applications, future opportunities and limitations. As an interdisciplinary field, advances are expected in both theoretical and experimental aspects of TENGs. For example, technologies based on Maxwell’s equations for a mechano-driven, slow-moving system can be coupled with a theoretical understanding of physical laws and concepts. From this, general simulation models can be established and corresponding experiments designed to optimize TENGs for a range of applications. Triboelectric nanogenerators (TENGs) convert mechanical energy into electric power by combining contact electrification and electrostatic induction. This Primer introduces the theoretical background of TENGs, gives an overview of fabrication methods and discusses how they can be applied as energy harvesting devices and self-powered systems.