A Bilayer High-Temperature Dielectric Film with Superior Breakdown Strength and Energy Storage Density

The further electrification of various fields in production and daily life makes it a topic worthy of exploration to improve the performance of capacitors for a long time,including thin-film capacitors.The discharge energy density of thin-film capacitors that serves as one of the important types directly depends on electric field strength and the dielectric constant of the insulation material.However,it has long been a great challenge to improve the breakdown strength and dielectric constant simultaneously.Considering that boron nitride nanosheets(BNNS)possess superior insulation and thermal conductivity owing to wide band gap and 2-dimensional structure,a bilayer polymer film is prepared via coating BNNS by solution casting on surface of polyethylene terephthalate(PET)films.By revealing the bandgap and insulating behavior with UV absorption spectrum,leakage current,and finite element calculation,it is manifested that nanocoating contributes to enhance the bandgap of polymer films,thereby suppressing the charge injection by redirecting their transport from electrodes.Worthy to note that an ultrahigh breakdown field strength(~736 MV m^(−1)),an excellent discharge energy density(~8.77 J cm^(−3))and a prominent charge-discharge efficiency(~96.51%)are achieved concurrently,which is ascribed to the contribution of BNNS ultrathin layer.In addition,the modified PET films also have superior comprehensive performance at high temperatures(~120°C).The materials and methods here selected are easily accessible and facile,which are suitable for large-scale roll-to-roll process production,and are of certain significance to explore the methods about film modification suitable for commercial promotion.

Ultrasmall barium titanate nanoparticles modulated stretchable dielectric elastomer sensors with large deformability and high sensitivity

Large deformability and high sensitivity is difficult to be realized simultaneously in flexible sensors.Herein,taking advantage of the high permittivity and highly active surfaces of the ultrasmall barium titanate nanoparticles(BT NPs)and the high stretchability of the p(BA-GMA)elastomer matrix,we propose a high-performance soft stretchable sensor.The addition of the ultrasmall BT NPs can not only increase the permittivity and capacitance of polyacrylate-matrix composite dielectric material to obtain a high sensitivity,but also basically maintains the excellent mechanical properties of the polymer matrix.The dielectric constants of the composite films increase from 5.68 to 13.13 at 10 kHz with the increase of BT NPs content from 0 to 15 vol.%,which results in a high capacitance of 236.16 pF for 15 vol.%BT/p(BA-GMA)sensor.Combining the high permittivity and the large deformability(a maximal deformation of 87.2%),the 15 vol.%BT/p(BA-GMA)sensor has high sensitivity and shows high linearity and stable output even if under dynamic measurement.The dual-mode sensor that utilizes the orthogonality of capacitance-resistance is designed,which shows excellent performance in monitoring human body movements and noncontact measurement.The results present that the BT/p(BA-GMA)-based sensor has high stability and reliability not exceed 65C,which can meet the application requirements in dynamic monitoring.

High-permittivity polymer nanocomposites: Influence of interface on dielectric properties

Flexible dielectric composites with high permittivity have been extensively studied due to their potential applications in highdensity energy capacitors.In this review,effects of interface characteristics on the dielectric properties in the polymer-based nanocomposites with high permittivity are analyzed.The polymer-based dielectric composites are classified into two types:dielectric–dielectric(DD,ceramic particle-polymer)composites and conductor–dielectric(CD,conductive particle-polymer)composites.It is highly desirable for the dielectric–dielectric composites to exhibit high permittivity at low content of ceramic particles,which requires a remarkable interface interaction existing in the composite.For conductor–dielectric composites,a high permittivity can be achieved in composite with a small amount of conductor particle,but associated with a high loss.In this case,the interface between conductor and polymer with a good insulating characteristic is very important.Different methods can be used to modify the surface of ceramic/conductor particles before these particles are dispersed into polymers.The experimental results are summarized on how to design and make the desirable interface,and recent achievements in the development of these nanocomposites are presented.The challenges facing the fundamental understanding on the role of interface in high-permittivity polymer nanocomposites should be paid a more attention.

Enhanced thermal conductivity and dielectric properties in electrostatic self-assembly 3D pBN@nCNTs fillers loaded in epoxy resin composites

High-performance epoxy(EP)composites with excellent thermal conductivity and dielectric properties have attracted increasing attention for effective thermal management.In this work,three-dimensional(3D)structural functional fillers were prepared by an electrostatic self-assembly approach.The negatively charged carbon nanotubes(nCNTs)prepared by carboxylation on the surface of CNTs were attached to the positively charged boron nitride(pBN)to form the 3D pBN@nCNTs functional fillers.The morphological characterizations of the formed 3D pBN@nCNTs fillers and epoxy composites were established,illustrating that nCNTs were linearly overlapped between the BN sheets,thus forming a 3D heat conduction network in the epoxy matrix.The synergistic effect of pBN with nCNTs on the enhancement of thermal conductivity and dielectric properties of composites was systematically studied.The experimental results demonstrated that the thermal conductivity of pBN@nCNTs/EP composites could reach 1.986 W m1K1 with the loading of 50 wt%fillers at 10:1 mass ratio of pBN:nCNTs,which is 464%and 124%higher than that of pure EP and BN/EP,respectively.Simultaneously,the dielectric permittivity was successfully increased to 15.14.Moreover,the thermal stability of the composites was synchronously enhanced.This study provides a facile path to fabricate thermosetting polymer composites with high thermal conductivity and dielectric properties.

Towards suppressing dielectric loss of GO/PVDF nanocomposites with TA-Fe coordination complexes as an interface layer

In this work, graphene oxide(GO) nanosheets with surface modification by Tannic and Fe coordination complexes(TA-Fe) were incorporated into poly(vinylidene fluoride)(PVDF) to prepare high constant but low loss polymer nanocomposites, and the effect of TA-Fe interlayer on dielectric properties of the GO@TA-Fe/PVDF nanocomposites was investigated. The results indicate that the dosage, mixing ratio, and reaction time of TA-Fe complexes have obvious influences on the dielectric properties of the nanocomposites. Furthermore, the TA-Fe interlayer significantly influences the electrical properties of GO@TA-Fe nanoparticles and their PVDF composites, and the GO@TA-Fe/PVDF composites exhibit superior dielectric properties compared with raw GO/PVDF. Dielectric losses of the GO@TA-Fe/PVDF are significantly suppressed to a rather low level owing to the presence of TA-Fe layer, which serves as an interlayer between the GO sheets, thus preventing them from direct contacting with each other. Additionally, the dynamic dielectric relaxation of the GO/PVDF and GO@TA-Fe/PVDF nanocomposites was investigated in terms of temperature.

Theoretical analysis and application of polymer-matrix field grading materials in HVDC cable terminals

The distortion and uneven distribution of electric field in high-voltage direct current(HVDC)terminal insulator is the key problem for stable running of the power transmission system.Semiconducting flexible materials filled polymer-matrix composites with non-linear conductivity have also been considered to modify the distribution of electric field in cable terminal.Several factors having influence on the non-linear conductivity will be analysed in this review.

A novel strategy of fabricated flexible ITO electrode by liquid metal ultra-thin oxide film

Flexible transparent conductive films are gaining attention day by day over the last few years due to it is a key component of next generation flexible electronics and optoelectronic devices.Indium tin oxide(ITO)as one of the most widely used transparent conductive material is limited by the traditional deposition approach cannot be achieve ultra-thin,which results in its brittle nature.Herein,a novel strategy for fabricating highly transparent conductive films by liquid metal interface phase separation technique based on low-melting liquid metal of InxSn100-x alloy is reported,during the solid-to-liquid phase transition of alloy,the monolayer of surface oxide film segregated with the bulk phase and was printed on the flexible polyethylene-naphthalate(PEN)substrate under the van der Waals.This novel strategy can directly print the ultra-thin self-oxide with the structure of ITO on PEN substrate,with the resulting of transparency over 97.5%and resistivity as low as 0.21 kU cm,providing a new way of lowcost raw ITO material as well as the personalized preparation strategy.The desirable highly transparent conductive films are comparable to recently reported ITO film,together with advantages of pretty steady,make them attractive as various flexible transparent conductive electrodes,for example,an ultra-thin ITO film is developed for luminescent devices.

Particle packing theory guided multiscale alumina filled epoxy resin with excellent thermal and dielectric performances

Polymers and composites with high thermal conductivity are promising yet challenging for the growing demand of thermal management in electrical and electronic equipment.Guided by the closest packing model,a multiscale filling Al_(2)O_(3) strategy was designed and incorporated with epoxy resin(EP)to form high thermal conductive composites in this work.Epoxy composites with single filler loading were also prepared.The microstructures,thermal,rheological,and dielectric characteristics of the multiscale filling Al_(2)O_(3)/EP composites have been investigated.Compared with single-scale Al_(2)O_(3) filled epoxy based composites,it is found that the multiscale filling Al_(2)O_(3)/EP composites exhibit higher thermal conductivity under the same filler loading of 50 vol%,which is attributed to the efficient heat conduction paths formed by appropriate multiscale fillers.Particularly,a remarkably improved thermal conductivity of 2.707 W m^(-1) K^(-1) was acquired in Al_(2)O_(3)/EP composites at filler loading of 50 vol%(5 mm Al_(2)O_(3)(26.67 vol%),30 mm Al_(2)O_(3)(27.41 vol%)and 70 mm Al_(2)O_(3)(45.92 vol%)),which is about 1300%higher than that of the pure epoxy resin.In addition,the dielectric constant of the Al_(2)O_(3)/EP composites were significantly improved while keeping the dielectric loss almost unchanged.The finite element simulation further verified the effectiveness of improving the thermal conductivity of materials in the heat dissipation of electrical equipment.Therefore,this research provides a simple strategy for manufacturing high thermal conductive composite materials with a wide range of potential applications as packaging materials.

Characterization of percolation behavior in conductor-dielectric 0-3 composites

The equationε_(eff)■/φ_(c)φ)^(s)which shows the relationship between effective dielectric constant(ε_(eff))and the filler concentration(φ),is widely used to determine the percolation behavior and obtain parameters,such as percolation thresholdφc and the power constant s in conductor-dielectric composites(CDCs).Six different systems of CDCs were used to check the expression by fitting experimental results.It is found that the equation can fit the experimental results at any frequency.However,it is found that the fitting constants do not reflect the real percolation behavior of the composites.It is found that the dielectric constant is strongly dependent on the frequency,which is mainly due to the fact that the frequency dependence of the dielectric constant for the composites close toφ_(c)is almost independent of the matrix.

Electrospun poly(ethylene oxide) nanofibrous composites with enhanced ionic conductivity as flexible solid polymer electrolytes

Solid polymer electrolytes(SPEs)have great potential to address the safety issues of lithium(Li)-ion batteries when compared with conventional liquid electrolytes,which makes them a promising alternative for next-generation high-energy batteries.In this work,poly(ethylene oxide)-lithium perchlorate(PEO–LiClO4)polymer electrolytes for Li-ion batteries were prepared using electrospinning.The crystallinity,ionic conductivity as well as mechanical properties were investigated.Ionic conductivities and mechanical properties of PEO–LiClO4 based SPE have been obviously increased by incorporating modified TiO2 nanofibres(TNFs)than TiO2 nanoparticles(TNPs),due to that both TNFs and TNPs can decrease the crystalline phase concentration of PEO and increase segmental flexibility of PEO.The SPE with 3 wt%TNFs exhibits the highest conductivity of 5.308×10−5 S cm−1 at 20°C and higher tensile strength of 13.8 MPa.These results highlight the potential of utilising the electrospinning method to improve the ionic conductivity of SPEs.

Theoretical investigations on the thiol–thioester exchange steps of different thioesters

As the rate-determining step in native chemical ligation reactions, the thiol–thioester exchange step is important in determining the efficiency of the ligations of peptides. In the present study, systematic theoretical calculations were carried out on the relationships between the structure of different thioesters and the free energy barriers of the thiol–thioester exchange step. According to the calculation results, the thiol–thioester exchange step is disfavored by the steric hindrance around the carbonyl center, while the electronic effect（i.e. conjugation and hyper-conjugation effects） becomes important when the steric hindrance is insignificant.