Process and Microstructure to Achieve Ultra-high Dielectric Constant in Ceramic-Polymer Composites

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Energy Storage Performance of Polymer-Based Dielectric Composites with Two-Dimensional Fillers

Dielectric capacitors have garnered significant attention in recent decades for their wide range of uses in contemporary electronic and electrical power systems. The integration of a high breakdown field polymer matrix with various types of fillers in dielectric polymer nanocomposites has attracted significant attention from both academic and commercial sectors. The energy storage performance is influenced by various essential factors, such as the choice of the polymer matrix, the filler type, the filler morphologies, the interfacial engineering, and the composite structure. However, their application is limited by their large amount of filler content, low energy densities, and low-temperature tolerance. Very recently, the utilization of two-dimensional (2D) materials has become prevalent across several disciplines due to their exceptional thermal, electrical, and mechanical characteristics. Compared with zero-dimensional (0D) and one-dimensional (1D) fillers, two-dimensional fillers are more effective in enhancing the dielectric and energy storage properties of polymer-based composites. The present review provides a comprehensive overview of 2D filler-based composites, encompassing a wide range of materials such as ceramics, metal oxides, carbon compounds, MXenes, clays, boron nitride, and others. In a general sense, the incorporation of 2D fillers into polymer nanocomposite dielectrics can result in a significant enhancement in the energy storage capability, even at low filler concentrations. The current challenges and future perspectives are also discussed.

Fabric-like Electrospun PVAc-Graphene Nanofiber Webs as Wearable and Degradable Piezocapacitive Sensors

Flexible piezocapacitive sensors utilizing nanomaterial-polymer composite-based nanofibrous membranes offer an attractive alternative to more traditional piezoelectric and piezoresistive wearable sensors owing to their ultralow powered nature, fast response, low hysteresis, and insensitivity to temperature change. In this work, we propose a facile method of fabricating electrospun graphene-dispersed PVAc nanofibrous membrane-based piezocapacitive sensors for applications in IoT-enabled wearables and human physiological function monitoring. A series of electrical and material characterization experiments were conducted on both the pristine and graphene-dispersed PVAc nanofibers to understand the effect of graphene addition on nanofiber morphology, dielectric response, and pressure sensing performance. Dynamic uniaxial pressure sensing performance evaluation tests were conducted on the pristine and graphene-loaded PVAc nanofibrous membrane-based sensors for understanding the effect of two-dimensional (2D) nanofiller addition on pressure sensing performance. A marked increase in the dielectric constant and pressure sensing performance was observed for graphene-loaded spin coated membrane and nanofiber webs respectively, and subsequently the micro dipole formation model was invoked to explain the nanofiller-induced dielectric constant enhancement. The robustness and reliability of the sensor have been underscored by conducting accelerated lifetime assessment experiments entailing at least 3000 cycles of periodic tactile force loading. A series of tests involving human physiological parameter monitoring were conducted to underscore the applicability of the proposed sensor for IoT-enabled personalized health care, soft robotics, and next-generation prosthetic devices. Finally, the easy degradability of the sensing elements is demonstrated to emphasize their suitability for transient electronics applications.

Contributing Factors of Dielectric Properties for Polymer Matrix Composites

Due to the trend of multi-function, integration, and miniaturization of electronics, traditional dielectric materials are difficult to satisfy new requirements, such as balanced dielectric properties and good designability. Therefore, high dielectric polymer composites have attracted wide attention due to their outstanding processibility, good designability, and dielectric properties. A number of polymer composites are employed in capacitors and sensors. All these applications are directly affected by the composite's dielectric properties, which are highly depended on the compositions and internal structure design, including the polymer matrix, fillers, structural design, etc. In this review, the influences of matrix, fillers, and filler arrangement on dielectric properties are systematically and comprehensively summarized and the regulation strategies of dielectric loss are introduced as well. Finally, the challenges and prospects of high dielectric polymer composites are proposed.

Facile fabrication of polystyrene particles/graphene composites for improved dielectric and thermal properties

In this paper, polystyrene (PS)-based reduced graphene oxide (rGO) composites were prepared by mixing PS latex particles with graphene oxide (GO) and the following in-situ reduction. The structure and morphology of PS/rGO composites were characterized, and the effects of rGO content on the dielectric properties as well as thermal stability of PS/rGO composites were investigated. Results showed that rGO sheets armoured on the surface of PS particles and exhibited well dispersion in the PS matrix after hot compression. The introduction of rGO improved the dielectric properties of the composites remarkably. When rGO content was 0.12 vol%, the dielectric permittivity and breakdown strength of PS/rGO arrived at 6.3 at10² Hz and 107 kV/mm, with 50% and 35.4% enhancement compared to the pristine PS. Furthermore, PS/rGO presented better thermal stability than the pristine PS, but the overlapping of rGO sheets in PS matrix induced the instability of dielectric loss with frequency.

Carbon Modification of K1.6Fe1.6Ti6.4O16 Nanoparticles to Optimize the Dielectric Properties of PTFE-Based Composites

In this work, polymer matrix composites with the compositions PTFE/KFTO(H) and PTFE/KFTO(H)@CB and with filler volume fractions of 2.5, 5.0, 7.5, 15, and 30% (without and with carbon modification at a content of 2.5 wt.% regarding ceramic material) were produced by calendering and hot pressing and studied using FTIR, SEM, and impedance spectroscopy methods. Ceramic filler (KFTO(H)) was synthesized using the sol−gel Pechini method. Its structure was investigated and confirmed by the XRD method with following Rietveld refinement. The carbon black (CB) modification of KFTO(H) was carried out through the calcination of a mixture of ceramic and carbon materials in an argon atmosphere. Afterwards, composites producing all the components’ structures weren’t destroyed according to the FTIR results. The effect of carbon additive at a content of 2.5 wt.% relating to ceramic filler in the system of polymer matrix composites was shown, with permittivity increasing up to ε’ = 28 with a simultaneous decrease in dielectric loss (tanδ < 0.1) at f = 103 Hz for composites of PTFE/KFTO(H)@CB (30 vol.%).

Improving the Energy Density and Efficiency of the Linear Polymer PMMA with a Double-Bond Fluoropolymer at Elevated Temperatures

A variety of applications can be found for high-temperature film capacitors, including energy storage components and pulsed power sources. In this work, in order to increase the energy density (U _e), poly(vinylidene fluoride-chlorotrifluoroethylene-double bond) (P-DB) is introduced into poly(methyl methacrylate) (PMMA) to manufacture composite films by a solution casting process. In the case of the pure PMMA film, there is significant improvement in the polarization (P _max) and breakdown field (E _b) of the composite film. These improvements can effectively increase the U _e of the composite film at room temperature and the elevated temperature. The results show that at an elevated temperature of 90 °C and at 350 MV/m, the U _e of 40 vol % P-DB reaches 8.7 J/cm³, and the efficiency (η) of 77% is also considerable. Compared with biaxially oriented polypropylene (2.0 J/cm³), the proposed film exhibits 4 times enhancement in the energy storage density, meaning that it can be an energy storage capacitor with huge potential at high temperatures.

Recent Advances on Conducting Polymers Based Nanogenerators for Energy Harvesting

With the rapid growth of numerous portable electronics, it is critical to develop high-performance, lightweight, and environmentally sustainable energy generation and power supply systems. The flexible nanogenerators, including piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG), are currently viable candidates for combination with personal devices and wireless sensors to achieve sustained energy for long-term working circumstances due to their great mechanical qualities, superior environmental adaptability, and outstanding energy-harvesting performance. Conductive materials for electrode as the critical component in nanogenerators, have been intensively investigated to optimize their performance and avoid high-cost and time-consuming manufacture processing. Recently, because of their low cost, large-scale production, simple synthesis procedures, and controlled electrical conductivity, conducting polymers (CPs) have been utilized in a wide range of scientific domains. CPs have also become increasingly significant in nanogenerators. In this review, we summarize the recent advances on CP-based PENG and TENG for biomechanical energy harvesting. A thorough overview of recent advancements and development of CP-based nanogenerators with various configurations are presented and prospects of scientific and technological challenges from performance to potential applications are discussed.

Prospects for the Development of High Energy Density Dielectric Capacitors

In this paper, the design of high energy density dielectric capacitors for energy storage in vehicle, industrial, and electric utility applications have been considered in detail. The performance of these devices depends primarily on the dielectric constant and breakdown strength characteristics of the dielectric material used. A review of the literature on composite polymer materials to assess their present dielectric constants and the various approaches being pursued to increase energy density found that there are many papers in which materials having dielectric constants of 20–50 were reported, but only a few showing materials with very high dielectric constants of 500 and greater. The very high dielectric constants were usually achieved with nanoscale metallic or carbon particles embedded in a host polymer and the maximum dielectric constant occurred near the percolation threshold particle loading. In this study, an analytical method to calculate the dielectric constant of composite dielectric polymers with various types of nanoparticles embedded is presented. The method was applied using an Excel spreadsheet to calculate the characteristics of spiral wound battery cells using various composite polymers with embedded particles. The calculated energy densities were strong functions of the size of the particles and thickness of the dielectric layer in the cell. For a 1000 V cell, an energy density of 100–200 Wh/kg was calculated for 3–5 nm particles and 3–5 µ thick dielectric layers. The results of this study indicate that dielectric materials with an effective dielectric constant of 500–1000 are needed to develop dielectric capacitor cells with battery-like energy density. The breakdown strength would be 300–400 V/µ in a reverse sandwich multilayer dielectric arrangement. The leakage current of the cell would be determined from appropriate DC testing. These high energy density dielectric capacitors are very different from electrochemical capacitors that utilize conducting polymers and liquid electrolytes and are constructed much like batteries. The dielectric capacitors have a very high cell voltage and are constructed like conventional ceramic capacitors.

Improved Energy Storage Performance of All-Organic Composite Dielectric via Constructing Sandwich Structure

Improving the energy storage density of dielectrics without sacrificing charge-discharge energy storage efficiency and reliability is crucial to the performance improvement of modern electrical and electronic systems, but traditional methods of doping high-dielectric ceramics cannot achieve high energy storage densities without sacrificing reliability and storage efficiency. Here, an all-organic energy storage dielectric composed of ferroelectric and linear polymer with a sandwich structure is proposed and successfully prepared by the electrostatic spinning method. Additionally, the effect of the ferroelectric/linear volume ratio on the dielectric properties, breakdown, and energy storage is systematically studied. The results show that the structure has good energy storage characteristics with a high energy storage density (9.7 J/cm³) and a high energy storage efficiency (78%). In addition, the energy storage density of the composite dielectric under high energy storage efficiency (90%) is effectively improved (25%). This result provides theoretical analysis and experience for the preparation of multilayer energy storage dielectrics which will promote the development and application of energy storage dielectrics.

The Dependence of Acoustic Emission Performance on the Crystal Structures, Dielectric, Ferroelectric, and Piezoelectric Properties of the P(VDF-TrFE) Sensors

To clarify the influence of various molar concentrations of vinylidene fluoride (VDF) on the piezoelectric and acoustic emission (AE) reception performances of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] sensors, we systematically investigated the crystal structures and the dielectric and ferroelectric properties of P(VDF-TrFE) films with different compositions of VDF and TrFE monomers and found that low proportion (<30 mol%) TrFE as a wedge inserted into molecular chains of P(VDF-TrFE) will not only improve the fraction of regular β -phase crystal grains but also decrease the dielectric constant ( ε_r ) of these copolymers, which favors the piezoelectric voltage coefficient ( g₃₃ ) of this P(VDF-TrFE) film. As such, a considerable remanent electric polarization ( [Formula: see text]/cm²) under 200 MV/m and a large piezoelectric coefficient ( d ₃₃  ∼ -25 pC/N) are obtained in P(VDF-TrFE) 80/20-mol% films. It is worth noting that a sensor made from P(VDF-TrFE) 80/20 mol% shows an attractive AE reception property of approximately 84 dB, a high signal voltage of above 10 mV from time-domain analysis, and a large signal voltage of above 4 mV from frequency-domain analysis, which are close to standard lead zirconate titanate (PZT) sensors. Considering its unique characters of flexibility, no required stretching, easily shaped, having high thermal Faille temperatures ( [Formula: see text]), etc., P(VDF-TrFE) piezoelectric film is considered a promising material for sensors, actuators, and energy transfer units.

Dielectric Properties of Graphene/Titania/Polyvinylidene Fluoride (G/TiO2/PVDF) Nanocomposites

Flexible electronics have gained eminent importance in recent years due to their high mechanical strength and resistance to environmental conditions, along with their effective energy storage and energy generating abilities. In this work, graphene/ceramic/polymer based flexible dielectric nanocomposites have been prepared and their dielectric properties were characterized. The composite was formulated by combining graphene with rutile and anatase titania, and polyvinylidene fluoride in different weight ratios to achieve optimized dielectric properties and flexibility. After preparation, composites were characterized for their morphologies, structures, functional groups, thermal stability and dielectric characterizations by using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and impedance spectroscopy. Dielectric results showed that prepared flexible composite exhibited dielectric constant of 70.4 with minor leakage current (tanδ) i.e., 0.39 at 100 Hz. These results were further confirmed by calculating alternating current (AC) conductivity and electric modulus which ensured that prepared material is efficient dielectric material which may be employed in electronic industry for development of next generation flexible energy storage devices.

Large Dielectric Constant Enhancement in MXene Percolative Polymer Composites

We demonstrate that poly(vinylidene fluoride) (PVDF)-based percolative composites using two-dimensional (2D) MXene nanosheets as fillers exhibit significantly enhanced dielectric permittivity. The poly(vinylidene fluoride-trifluoro-ethylene-chlorofluoroehylene) (P[VDF-TrFE-CFE]) polymer embedded with 2D Ti₃C₂T _x nanosheets reaches a dielectric permittivity as high as 10⁵ near the percolation limit of about 15.0 wt % MXene loading, which surpasses all previously reported composites made of carbon-based fillers in the same polymer. With up to 10 wt % MXene loading, the dielectric loss of the MXene/P(VDF-TrFE-CFE) composite indicates only an approximately 5-fold increase (from 0.06 to 0.35), while the dielectric constant increased by 25 times over the same composition range. Furthermore, the ratio of permittivity to loss factor of the MXene-polymer composite is superior to that of all previously reported fillers in this same polymer. The dielectric constant enhancement effect is demonstrated to exist in other polymers as well when loaded with MXene. We show that the dielectric constant enhancement is largely due to the charge accumulation caused by the formation of microscopic dipoles at the surfaces between the MXene sheets and the polymer matrix under an external applied electric field.

Innovative Linear Low Density Polyethylene Nanocomposite Films Reinforced with Organophilic Layered Double Hydroxides: Fabrication, Morphology and Enhanced Multifunctional Properties

Herein, we reported the successful development of novel nanocomposite films based on linear low density polyethylene (LLDPE) with enhanced anti-drop, optical, mechanical, thermal and water vapor barrier properties by introducing organophilic layered double hydroxides (OLDHs) nanosheets. OLDHs loadings were varied from 0–6 wt.%. Structural analyses using the Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) indicated that the OLDHs nanosheets were homogeneously dispersed with an ordered alignment in the LLDPE matrix. The LLDPE film containing 2 wt.% OLDHs (denoted as OLDHs-2) showed the optimal mechanical, thermal and water vapor barrier properties, whilst the anti-drop and optical performance of the films improved with increasing OLDHs content. The enhanced antidrop properties of the composite films relative to pristine LLDPE can be expected to effectively reduce agricultural losses to disease when the films are applied as agricultural films, whilst the superior light transmittance and water-retaining properties of the composite films will boost agricultural production. Results presented suggest that multifunctional LLDPE/OLDHs nanocomposites show great promise as low cost agricultural plastic films.

Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers

There is a growing need for high energy density capacitors in modern electric power supplies. The creation of nanocomposite systems based on one-dimensional nanofibers has shown great potential in achieving a high energy density since they can optimize the energy density by exploiting both the high permittivity of ceramic fillers and the high breakdown strength of the polymer matrix. In this paper, BaTiO3 nanofibers (NFs) with different aspect ratio were synthesized by a two-step hydrothermal method and the permittivity and energy storage of the P(VDF-HFP) nanocomposites were investigated. It is found that as the BaTiO3 NF aspect ratio and volume fraction increased the permittivity and maximum electric displacement of the nanocomposites increased, while the breakdown strength decreased. The nanocomposites with the highest aspect ratio BaTiO3 NFs exhibited the highest energy storage density at the same electric field. However, the nanocomposites with the lowest aspect ratio BaTiO3 NFs achieved the maximal energy storage density of 15.48 J/cm3 due to its higher breakdown strength. This contribution provides a potential route to prepare and tailor the properties of high energy density capacitor nanocomposites.