Flexible Dielectric Materials Research Articles

Cellulose/BaTiO3 nanofiber dielectric films with enhanced energy density by interface modification with poly(dopamine)

Flexible electrostatic capacitors have many potential applications in modern electric power systems. In this study, flexible cellulose-based dielectric films were prepared by compositing regenerated cellulose (RC) and one-dimensional BaTiO3 nanofiber (BTNF) via a simple and environmentally friendly process. To improve compatibility and distributional homogeneity of the fillers/matrix, BTNF was surface modified by dopamine to prepare the poly(dopamine) modified BTNF (PDA@BTNF). The obtained RC/PDA@BTNF composite films (RC-PDA@BTNF) possessed higher dielectric constant and breakdown strength than those of the RC and RC/BTNF composite films. In particular, RC/PDA@BTNF composite films with 2 vol% PDA@BTNF (RC-2PDA@BTNF) exhibited a high discharged energy density of 17.1 J/cm3 at 520 MV/m, which exceeded 40 % compared with that of RC-2BTNF at 460 MV/m. Meanwhile, RC-2PDA@BTNF could continuously work for more than 10,000 times with a high efficiency of 91 %. Furthermore, the composite films could maintain good dielectric properties for a long time when stored in vacuum condition (under 0.3 atm). Therefore, these flexible cellulose-based dielectric materials are promising in the field of novel high-performance film dielectric capacitors.

Ultrahigh energy-density flexible dielectric films achieved by self-bundled polymer nanocluster in necklace-like arrangement

Flexible dielectric materials with ultrahigh energy density (Ue) is of critical importance to reduce the size of dielectric capacitors, which has recently drawn ever-increasing attention. Herein, different from the incorporation of traditional 1D/2D inorganic nanofiller into single/multi-layer polymer matrix, a multifunctional poly (p-phenylene terephthalamide) (PPTA)-based derivative fluxible polymer (f-PPTA) nanocluster is selected and introduced to typical ferroelectric poly (vinylidene fluoride) (PVDF) matrix. As a novel polymer-based nanofiller, the f-PPTA nanocluster consists of self-bundled parallel sulfonated PPTA skeleton and grafted with octadecylamine polyoxyethylene ether amphiphilic (PEGO) amine ligand through ionic interaction. In the multi-arm amphiphilic PEGO, one alkyl chain with the length of 15 carbon atoms provides similar hydrophobic nature to that of PVDF, which contributes to improving the interfacial compatibility between polymer nanocluster and matrix. Furthermore, the relatively short hydrophilic chain with the length of 8 carbon atoms induces a specific necklace-like arrangement of the f-PPTA nanoclusters in PVDF matrix during film fabrication spontaneously. Consequently, an ultrahigh Ue ~ 22.5 J•cm−3 of the dielectric film is acquired at 600 MV•m−1 electric field. This value is the highest reported so far among all the poly (vinylidene fluoride) (PVDF)-based dielectric nanocomposites to the best of our knowledge. In addition, the elongation at break of the film can be increased to 390%, which is over 9 times that of pure PVDF sample. This work provides a new route to PVDF-based polymer nanocomposites with ultrahigh Ue and highly stretchable performance.

Design and Properties of Fluoroelastomer Composites via Incorporation of MWCNTs with Varied Modification

Multi-walled carbon nanotubes (MWCNTs) modified with silane coupling agent A-1120 (MWCNTs-A1120) were prepared. Compared with the raw MWCNTs, acidified MWCNTs (MWCNTs-COOH), and MWCNTs grafted with EDA (MWCNTs-NH2), MWCNTs-A1120 have the best dispersion in fluoroelastomer at the same doping ratio. Therefore, fluoroelastomer/MWCNTs-A1120 composite has the best mechanical properties with tensile strength of 13.92 MPa and elongation at break of 111.78%. Then, the effects of doping amount of MWCNTs-A1120 on the electrical properties of the composites were investigated. The dielectric constant of the composite increases with the increase of MWCNTs-A1120, and the dielectric loss does not change much at the low doping amount such as 0.5 wt%. When the doping amount of MWCNTs-A1120 is 5 wt%, the dielectric constant and the dielectric loss value are greatly increased, and the volume resistivity is greatly decreased, which proves that the conductive network is formed in the composite, so the filling amount of 5 wt% is the percolation threshold. The tensile deformation of the sample also affects the electrical properties of the composites. As the tensile deformation increases, the dielectric constant and dielectric loss of the composite decrease. For the composite with 5 wt% MWCNTs-A1120, excessive tensile deformation will destroy the conductive network structure of the composite, so the composite will change from conductive material to dielectric material. Therefore, such composite is a good candidate for flexible conductive material or flexible dielectric material used in harsh environments such as high temperatures and various aggressive solvents.

Polyvinyl butyral composites containing halloysite nanotubes/reduced graphene oxide with high dielectric constant and low loss

Polymer-based composites with high dielectric constant and low loss are highly desirable due to their inherent advantages of easy processability, flexibility, and lightweight. Herein, a functional nanofillers, halloysite nanotubes (HNTs) decorated reduced graphene oxide (rGO) hybrid microstructures (HNTs@rGO) was successfully prepared via controllable electrostatic self-assembly and in-situ heat reduction method. These hybrid microstructures combine characteristics of natural 1D ceramic nanotubes with large aspect ratio and high electric conductivity of rGO micro-sheets, which provided ideal material collocation in the construction of microcapacitors. The HNTs not only effectively prevented direct contact between the rGO micro-sheets in the composites but also played an important role in forming dielectric interface within microcapacitors. Consequently, an HNTs@rGO/polyvinyl butyral (PVB) composites containing a very low content of 5 wt% rGO exhibited an ultra-high dielectric constant of 150 and an extremely low loss of 0.12 at 103 Hz. It is believed that the unique characteristics and facile fabrication process of HNTs@rGO/PVB composite make it a potentially excellent candidate for flexible polymer-based dielectric materials applied in the capacitor fields.

Graphene@poly(dopamine)-Ag core–shell nanoplatelets as fillers to enhance the dielectric performance of polymer composites

A new type of core–shell graphene@poly(dopamine)-Ag nanoplatelets was developed to improve the dielectric properties of thermoplastic polyurethane (TPU) nanocomposites. Dopamine was oxidatively polymerized to form a polydopamine (PDA) layer on the surface of graphene nanosheets (Gns), and then Ag nanoparticles were chemically reduced by silver nitrate and uniformly embedded on the surface of PDA. This obtained Gns@PDA-Ag core–shell nanoplatelets were filled into TPU to prepare a flexible dielectric material. The microstructure and dielectric performances were tested. Results indicated that the Gns@PDA-Ag core–shell nanoplatelets were evenly dispersed in TPU matrix. Moreover, the addition of Gns@PDA-Ag core–shell nanoplatelets could effectively improve the dielectric constant of the composite. Under low-frequency test conditions, the dielectric constant of the TPU/Gns@PDA-Ag (4 wt%) nanocomposite was 117.81, which was about 14 times higher than that of pure TPU. Theoretical analysis shows that the PDA shell not only promoted the uniform dispersion of Gns in TPU matrix, but also enhanced the interface bonding between the nanoplatelets and the TPU matrix. Moreover, introducing ultra-small Ag nanoparticles had effectively decreased the dielectric loss and conductivity of TPU/Gns@PDA-Ag composites due to its coulomb blockade and quantum trapped carrier structure effects, which resulted in the improvement of energy storage characteristics of composite.

Evaluation of cure characteristic, physico‐mechanical, and dielectric properties of calcium copper titanate filled acrylonitrile‐butadiene rubber composites: Effect of calcium copper titanate loading

AbstractCalcium copper titanate (CCTO) has been synthesized by high temperature solid‐state reaction from calcium carbonate, copper (II) oxide, and titanium dioxide as the starting materials. The formation and morphology of CCTO were confirmed by X‐ray diffraction, Fourier‐transformed infrared spectrophotometry, scanning electron microscopy (SEM), and particle size analysis. In order to develop flexible dielectric materials, acrylonitrile‐butadiene rubber (NBR)‐based composites were prepared with CCTO content varied from 0 to 120 phr (parts per hundred rubber). The cure characteristics of composites were assessed. High‐dielectric constant CCTO particles were blended into NBR to make composites with improved dielectric constant. Results showed that the NBR/CCTO composites had a high dielectric constant (10–20) with low dielectric loss (<0.4) and low conductivity (<10−3 μS/cm) at frequencies up to 106 Hz. However, the higher CCTO loadings had agglomeration in the NBR matrix, and thus tensile strength and elongation at break sharply deteriorated due to poor rubber‐filler interactions. The results showed lower storage modulus E′ and a reduction in Tg with the incorporation of CCTO in NBR matrix. Moreover, improved thermal stability of the NBR/CCTO composites was achieved. SEM was used to observe the dispersion of CCTO particles in NBR matrix.

Analysis of different fixed and flexible dielectric materials on microstrip patch antenna for ISM band applications

Recently, advancement in wearable technologies, one challenging improvement is textile antenna. The most requirements of textile antennas are dielectric materials which include fabric substrate and the structure of the antenna. The characteristics of the antenna depends on the substrate material. The dielectric value of the fabric material can be calculated from the operating frequency of patch antenna. In this paper the micro strip patch antenna is designed for ISM band applications. The main objective of this paper is to design and compare the performance of the micro strip patch antenna on different fixed and flexible dielectric material like FR-4, RT DUROID 6010, Polystyrene, Teflon, Quartz, Cotton, Alumina, Polyester with different constant in terms of gain, return loss, radiation patterns The proposed antenna operate at the resonant frequency 2.45GHz(ISM band) with low return loss and high gain and directivity.The size of the designed antenna has been also miniaturized.

Flexible high dielectric thin films based on cellulose nanofibrils and acid oxidized multi-walled carbon nanotubes.

Flexible high dielectric materials are of prime importance for advanced portable, foldable and wearable devices. A series of flexible high dielectric thin films based on cellulose nanofibrils (CNF) and acid oxidized multi-walled carbon nanotubes (o-MWCNT) was prepared in aqueous solution. Though no organic solvent was involved during the preparation, the SEM images showed that o-MWCNTs have good distribution within the CNF matrix. The dielectric constant of CNF/o-MWCNT (6.2 wt%) composite films was greatly increased from 25.24 for pure CNF to 73.88, while the loss tangent slightly decreased from 0.70 to 0.68, and the AC conductivity decreased from 3.15 × 10−7 S cm−1 for CNF to 1.77 × 10−7 S cm−1 (at 1 kHz). The abnormal decrease of loss tangent and AC conductivity were attributed to the introduction of oxide-containing groups on the surface of MWCNTs. The nanocomposite films showed excellent flexibility such that they could be bent a thousand times without visible damage. The presence of MWCNTs also helped to improve the thermal stability of the composite films. The excellent dielectric and mechanical properties of the CNF/o-MWCNT composite film demonstrate its great potential to be utilized in the field of energy storage.

Energy storage enhancement of P(VDF-TrFE-CFE)-based composites with double-shell structured BZCT nanofibers of parallel and orthogonal configurations

Recent research in the development of flexible polymer dielectric materials for the conversion of electrical energy is springing up. A state-of-the-art energy-storage polymer-based composite with the potential of improving the performances (energy-storage density and efficiency) at the low electric field strength is proposed here. The ferroelectric polymer P(VDF-TrFE-CFE) (PVTC) blending with linear polymethyl methacrylate (PMMA) is used as the matrix to ensure higher polarization and lower energy loss. Meanwhile, the inorganic 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZCT) nanofibers work as the filler, and the double transition layers of core-shell structure (Al2O3+SiO2) serve as the interface. Finally, P(VDF-TrFE-CFE)-based composites with double-shell structured BZCT nanofibers of parallel and orthogonal configurations were fabricated. The effects of microstructure information (matrix, filler, interface) together with different configurations (parallel and orthogonal configurations) of BZCT@Al2O3@SiO2 nanofibers on the performances of nanocomposites were systematically and primarily discussed. Importantly, the Orthogonal BZCT@A@S⊥PVTC + PM composite with 3 vol% BZCT@A@S NFs possessed an excellent discharged energy density (~20.1 J/cm3) with charge-discharge efficiency of ~58.6% at ~440 kV/mm; meanwhile, the in-plane thermal conductivity of it reaches to ~0.33 W/(m·K). Referring to the experimental findings and simulation results, a mechanism related to rapidly polarized ferroelectric filler was proposed.

C-shaped split ring resonator terahertz toroidal dipole metasurfaces

We designed and fabricated terahertz toroidal dipole metasurfaces based on a C-shaped split ring resonator metallic pattern fabricated on a flexible dielectric material (mylar). The toroidal dipole moment (Ty) was demonstrated as the dominant contribution to two different resonances at low frequency (ω1) and at high frequency (ω2). Simulation and LC circuit model analysis offered a quantitative explanation to the blue shift of the resonant frequencies at ω1 and ω2 as the increase of the opening angle(θ). The resonant frequencies showed a red shift at ω1 and ω2 as the increase of the outer ring radius (QR). Furthermore, the enhancement of the Q factor was attributed to the increase of Ty and the decrease of radiative loss. It was further proven that the model provided a new scheme for designing the toroidal dipole metasurfaces under a terahertz band, which was expected to be used as terahertz functional devices.

High-K dielectric sulfur-selenium alloys.

Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.

High performance polyimide-based composites filled with 2D aluminum oxide coated reduced graphene oxide nanosheets

Two-dimension (2D) graphene-like nanosheets with small thickness and large lateral size attract tremendous attention in the application of high-K materials. In this paper, 2D aluminum oxide coated reduced graphene oxide nanosheet (Al2O3@rGO) were fabricated via bottom-up method in expectation of being a kind of promising dielectric filler. Polyimide (PI) based composites filled by different Al2O3@rGO contents were prepared via in-situ polymerization. The characterization results of the composites indicate that strong filler-matrix bonding contributes to improve the compatibility of Al2O3@rGO in PI. Besides, the orientation of Al2O3@rGO nanosheets in the composites is detected by SAXS and SEM. For the composites, the dielectric behaviors, thermal stabilities and mechanical properties were investigated. The results show that the composites possess high dielectric constant and low dielectric loss. Additionally, the composites have good electrical insulation properties. Furthermore, the enhancements in thermal stabilities and mechanical properties of the composites are also observed attribute to the strong interactions between PI and Al2O3@rGO. Consequently, it is hoped that the composites would be possessing potential applications in flexible dielectric materials owing to its enhanced dielectric constant, thermal stabilities and mechanical performances.

Dielectric and impedance spectroscopic studies of three phase graphene/titania/poly(vinyl alcohol) nanocomposite films

• G/TiO 2 /PVA nanocomposite films were synthesized with various concentrations of graphene and TiO 2 fillers to enhance dielectric and impedance efficiency of PVA. • Dielectric and impedance studies of G/TiO 2 /PVA nanocomposite films was carried out. • G/TiO 2 /PVA with weight fraction of 3:20:100 has many folds better dielectric and impedance properties than neat PVA. Flexible dielectric polymer composites with high dielectric permittivity and low dielectric loss have many applications in different areas of electronic industry. In this paper, we propose synthesis of flexible dielectric materials with efficient dielectric properties. We increased dielectric efficiency of poly(vinyl alcohol) by reinforcement of conducting graphene and rutile titania fillers in different weight fractions. The superiority of this method is that synthesized three phase graphene/titania/poly(vinyl alcohol) nanocomposite films have high dielectric permittivity, low dielectric loss and are flexible. Our results show that graphene/titania/poly(vinyl alcohol) with weight/weight fraction of 3:20:100 bears dielectric permittivity of 330 at 20 Hz that is about 36 times larger than that of neat PVA at same frequency. At this frequency above mentioned graphene/titania/poly(vinyl alcohol) nanocomposite has loss tangent of 4.39 acceptable for dielectrics in embedded capacitors and AC conductivity of 1.6 × 10 −6 Sm −1 that is much greater than that of neat PVA i.e; 6.5 × 10 −9 Sm −1 . Complex impedance spectroscopy, complex electric modulus and Cole-Cole plots of synthesized graphene/titania/poly(vinyl alcohol) nanocomposite films further confirm its better capacitive performance.

Luminescent and Transparent Nanocellulose Films Containing Europium Carboxylate Groups as Flexible Dielectric Materials

Transparent, flexible, and luminescent 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibril films with europium carboxylate groups (TOCN-Eu) are proposed as potential flexible dielectric materials. The TOCN-Eu films were prepared from TOCN films with sodium carboxylate groups (TOCN-Na) by immersion in Eu(NO3)3 solution and subsequent washing with water and drying of the wet TOCN-Eu hydrogel films. The nanolayered TOCN-Eu films emit red light under ultraviolet-light irradiation and exhibit greatly improved dry and wet mechanical properties, water resistance, thermal stability, oxygen-barrier properties, dielectric breakdown strength, and energy density than conventional TOCN-Na films. These characteristic properties of the TOCN-Eu films are most likely caused by the formation of strong ionic bonds between the carboxylate groups and Eu3+ ions. These high-performance cellulose nanofibril films are promising for application as multifunctional materials in light-emitting, photovoltaic, an...

Two-Dimensional High-k Nanosheets for Dielectric Polymer Nanocomposites with Ultrahigh Discharged Energy Density

Flexible dielectric materials with high electrical energy densities are of crucial importance in advanced electronics and electric power systems. The conventional methods for fabricating flexible d...

Optically transparent and high dielectric constant reduced graphene oxide (RGO)-PDMS based flexible composite for wearable and flexible sensors

Optically transparent flexible materials possessing high dielectric constant have tremendous applications in wide range applications such as flexible electronics devices, micro-electro-mechanical systems(MEMS),wearable sensors and biomedical devices. Out of all the polymers, PDMS(Polydimethylsiloxane) is very well known for its excellent properties and being utilized for biomedical devices and microfluidic applications. However, due to the poor electrical properties both electrical conductivity and dielectric constant, this material is not utilized as a sensing material for fabrication of wearable sensors or electronic devices. Though, some progress has been achieved to improve the conductivity of this material, for this purpose higher vol.% filler material is employed, that generate cracks and defects. Therefore, utilizing this material for the resistive based sensor fabrication is not that promising and also several applications such as touch screens, wearable electronics, touch sensors for keyboards, flexible switches and human-machine interfacing applications require capacitive-based sensors. In this work, we have developed a transparent flexible composite dielectric material by employing a very low vol.% chemically treated RGO as a filler in the PDMS matrix. The impacts of the uniform distribution of the RGO in the PDMS based composite’s flexibility, optical transparency and dielectric constant are investigated. The uniform distribution of the RGO in the PDMS matrix is obtained by the chemical treatment process prior to the fabrication of the composite, that helps to improve the flexibility of the composite material by improving the cross-linking bond between the RGO and PDMS matrix. Moreover, by controlling the uniform distribution of the RGO, it is possible to obtain 82% transparency with high dielectric constant(38) flexible composite material. We believe that this optical transparent and flexible composite can possibly be utilized for capacitive based wearable sensors, touch screens, touch sensors, flexible switches and flexible MEMS applications.

Dielectric and energy harvesting properties of FeTiNbO6/PVDF composites with reinforced sandwich structure

Flexible dielectrics have been the major enabler for a number of applications in advanced electronic and electrical power systems. As an important flexible dielectric material, polymer composites are promising in raising the poor dielectric properties of neat polymer of current use. In this study, a class of topological‐structure modulated multilayer composites comprising a percolation layer (FeTiNbO6[FTN]/polyvinylidenefluoride [PVDF]) intercalated between two insulating layers (PVDF or BaTiO3[BT]/PVDF) are assembled into sandwich structures by a facile hot‐pressing method. For the prepared sandwich structure, FTN/PVDF film acts as a semiconductive layer to raise dielectric permittivity, while two insulating layers at top and bottom of composite are used to suppress conductivity and dielectric loss. Resulted from the unique performances of the FTN/PVDF film and strong interfacial polarization, the sandwich composite possesses improved dielectric and insulation properties. Moreover, compared with FTN/PVDF, the BT20‐FTN40‐BT20 has lower dielectric loss and higher insulation properties, and after poling at 20 kV/mm for 6 h, it exhibits excellent vibration energy harvesting properties in cantilever mode. Thus, a piezoelectric energy harvester constructed from this sandwich composite can be used for self‐driving wireless sensors. POLYM. COMPOS., 40:E570–E578, 2019. © 2018 Society of Plastics Engineers

Nanofibers of poly(vinylidene fluoride)/copper nanowire: Microstructural analysis and dielectric behavior

The combination of copper and dielectric materials have emerged as one of the most promising alternatives for the next generation of charge storage devices and microelectronic integrated circuits. In this work, copper nanowires (CuNW) were synthesized using a hard template technique, where copper was electrodeposited into and then liberated from porous alumina templates. Flexible nanofibers of poly(vinylidene fluoride)/copper nanowire (PVDF/CuNW) at different loadings were then obtained using the technique of electrospinning. SEM and TEM images showed that the CuNW had a straight, rigid structure with an average length and diameter of 1.5 µm and 30 nm, respectively. The morphological characterizations also revealed that the CuNW were embedded and aligned inside the nanofibers of PVDF, leading to an increase in the diameters of the generated electrospun nanofibers, e.g., 154 nm and 227 nm for pure PVDF and PVDF/CuNW (20 wt%), respectively. The polymorphic behavior of the PVDF/CuNW nanofibers was studied by FTIR and WAXD, confirming the positive impact of electrospinning on piezoelectric β phase formation of the PVDF matrix. Dielectric measurements indicated that the real permittivity of the mats of the nanofibers increased with CuNW loading. The ascending trend of the real permittivity with the filler content was ascribed to the formation of nanocapacitor structures, i.e., the copper conductive nanofillers acting as nanoelectrodes and the polymer matrix as nanodielectrics. Thus, the results of this study showed that the electrospun PVDF/CuNW nanofibers could be suitable in applications where flexible dielectric and piezoelectric materials are required.

Cellulose nanofibril/boron nitride nanosheet composites with enhanced energy density and thermal stability by interfibrillar cross-linking through Ca2+

Flexible and eco-friendly dielectric materials with high energy density and breakdown strength have promising applications in energy storage devices.

Improved dielectric behaviour of graphene oxide-multiwalled carbon nanotube nanocomposite

We have prepared graphene oxide (GO)-multiwalled carbon nanotube (MWCNT) composite film through vacuum filtration method. In this work, we carried out the dielectric behaviour of GO-MWCNT composite film in the frequency range of 100 Hz to 1 MHz and temperature range of 30–200 °C. The GO-MWCNT composite film showed significantly higher dielectric constant as 6021 than the GO (5031) which was even very high compared to conventional dielectric materials. The enhancement of dielectric constant is attributed to the strong interaction between sp2 MWCNT fillers and sp3 GO matrix as well as the formation of microcapacitors by highly conductive MWCNT segregated by GO sheets. Furthermore, we found interesting transition between semiconductor to conductor was attained at 165 °C. It is suggested that the temperature dependent transition of electrical properties of GO-MWCNT composite film is closely related with the ion mobility, removal of water molecules and reduction of GO in the composite. The effect of interfacial polarization and relaxation process were studied. The redox peak current has increased significantly for the GO-MWCNT composite electrode than the GO and MWCNT where the highly conducting MWCNT provide the necessary conduction pathways on the electrode surface. These flexible, high dielectric constant nanocomposites are potential flexible dielectric materials for use in high frequency capacitors and in electronic devices.