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A theoretical study on the multi-channel hydrogen addition of maleimide containing 2-hydroxy-benzophenone onto polyethylene in ultra-violet (UV) radiation cross-linking process was carried out using density functional theory (DFT) method at the B3LYP/6–311 + G(d,p) level. The energetic information and the minimum energy path (MEP) are calculated for nine reaction channels. The electrophilic addition reactions at two positions in the target molecule (maleimide containing 2-hydroxy-benzophenone) were investigated, which are on the C atom of C = C groups and on the O atom of C = O groups. Frontier molecular orbitals (MOs) and natural bond orbital (NBO) charge population of the target molecule have been analyzed in detail. As a result, the reaction site of C in C = C group is more active than the site of O in C = O groups. The target molecule can be used as a multi-functional additive candidate. The predicted mechanism may provide a theoretical basis for the real application of cross-linked polyethylene (XLPE) high-voltage insulation cables.

Adding voltage stabilizer is a promising method to develop high-performance polymer insulating materials for HVDC cables. In this chapter, voltage stabilizers are classified into three categories according to the different mechanisms of inhibiting electrical tree initiation, namely inhibiting partial discharge, capturing high-energy electrons and inhibiting macromolecular degradation. The hot research topics and relevant research progresses of voltage stabilizer as well as the influences of voltage stabilizers on the DC insulation performances of polymer insulating materials are summarized. The satisfactory progress has been made by relevant researches on alkylated voltage stabilizer, quantum chemical calculation and the combined use of voltage stabilizer and nanoparticles, which are the hot research topics of voltage stabilizer recently. The voltage stabilizers exhibit excellent effects on improving the DC breakdown strength and DC electrical tree resistance of the polymeric insulations including polyethylene and polypropylene. The proper use of voltage stabilizers also has positive effects on inhibiting space charge accumulation in polymeric insulation. However, the mechanism of voltage stabilizers’ effects on the charge transport behaviors in polymeric insulation and how to use voltage stabilizer to regulate the charge transport need further study.

Space charge accumulated in insulation materials could result in local field distortion, accelerate the material aging and threaten the security of high voltage direct current (HVDC) cable. To suppress the space charge accumulation and improve the direct current (DC) electrical characteristics of crosslinked polyethylene insulation materials, crosslinked polyethylene/polypyrrole (XLPE/PPy) nanocomposites were prepared, and the DC conduction and breakdown strength were investigated. The XLPE/PPy nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The DC electrical characteristics measurement results showed that the introduction of nano-polypyrrole (nano-PPy) could reduce the DC electrical conduction current density of XLPE/PPy nanocomposites, improve the space charge distribution but not affect the crosslinking reaction and crystallinity of XLPE. While assuring excellent electrical conduction and space charge distribution characteristics, there was an optimum nano-PPy content to reduce the DC breakdown strength of XLPE/PPy nanocomposites insignificantly.

Theoretical investigation on the reaction of maleic anhydride (MAH) in the UV radiation cross-linking process of polyethylene as high voltage cable insulation materials is accomplished at B3LYP/6-311 + G(d,p) level. The reaction potential energy information of 10 reaction channels is identified. The results show that the UV radiation cross-linking reaction of polyethylene is initiated by benzophenone, and the multi-functional crosslinker triallyl isocyanurate (TAIC) is needed to take part in the cross-linking process. The behavior of grafting the polar group MAH onto the polyethylene is explored in detail at atomic and molecular levels during UV radiation cross-linking process. The investigation is expected to provide reliable information for optimizing polyethylene UV radiation cross-linking process and for the development of the insulation material of high-voltage cable exceed 500 kV in real applications.

A melt-blending process was adopted to prepare a 5 wt% and 150 μm thick SiO 2 /LDPE (Low-Density Poly-Ethylene) composite film, to study the influence of the microstructure evolution of the composite film on its conductivity when the temperature changes. The results show that there is an interface layer between SiO 2 and PI polymer matrix in composite film. When temperature varies from 30 °C to 100 °C, the interfacial thickness increases from 2.8 nm to 3.5 nm, and remains constant beyond 100 °C. DSC (Dynamic Stability Control) shows that this increase is mainly caused by the melting of lamellae of polyethylene polymer chains. DMA (Dynamic Mechanical Analyzer) indicates the bound effect of the interface on the polymer chains of the composite film. When temperature changes from 30 °C to 70 °C at the heating rate of 10 °C/min, the conductivity values of LDPE and SiO 2 /LDPE change from 1 × 10 −16 to 1 × 10 −14 s/m, 1.5 × 10 −16 to 1.7 × 10 −16 s/m, respectively. The conductivity of the composite film becomes 2 orders of magnitude smaller than that of pure polyethylene film. The increases of interface layer limit the space charge accumulation effectively, and lowers the sensitiveness of conductivity to temperature, resulting in significant improvement of insulating property.

Herein, a theoretical investigation on the reaction of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene is conducted at the B3LYP/6-311+G(d,p) level for the production of high voltage cable insulation materials, where the reaction potential energies of 10 reaction channels are identified. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities of the raw materials, product, and by-product in polyethylene insulation composite products are obtained. Furthermore, the optimized process for the production of UV radiation cross-linking polyethylene insulation materials for high voltage cables is described. The results indicate that the UV radiation cross-linking reaction of polyethylene is initiated by benzophenone, and the multi-functional cross-linker TAIC is required for the cross-linking process to occur. This investigation is expected to provide reliable information for the optimization of the polyethylene UV radiation cross-linking process and the development of insulation materials for high-voltage cables that can withstand more than 500 kV in real applications.

In this article, polyaniline (PANI) nanofibers were prepared and added to low-density polyethylene (LDPE) to produce PANI nanofibers/LDPE composites. LDPE and the composites were tested for direct current (DC) conductivity, breakdown strength, and space charge characteristics. The results suggested that DC breakdown strength of PANI nanofibers/LDPE composites significantly declined once PANI was added, and the decline was more evident with the increase of PANI nanofibers. Meanwhile, the addition of PANI nanofibers contributed to a decrease in the conductivity of LDPE. As the content of PANI nanofibers increased, the conductivity of the composites declined first and then raised. DC conductivity properties of LDPE could be improved by adding an appropriate amount of PANI nanofibers. Compared with LDPE, the space charge distribution was changed in LDPE due to the addition of PANI nanofibers. With the increase of content of PANI nanofibers, the amount of space charges close to the electrodes decreased gradually.

In order to systematically investigate the effects of nano-SiO 2 on the AC and DC electrical treeing resistance properties of XLPE, nano-SiO 2 /XLPE composite with the doping rate of 1wt% was prepared using parallel twin screw extruder. An electrical tree real-time observation system was designed. With untreated XLPE and commercial available XLPE for DC cable insulation as reference, the doping effects of nano-SiO 2 on the electrical tree initiation and growth characteristics under AC voltage and periodically grounded DC voltage were tested under different voltages using needle-plate electrode system. The test results indicate that: the periodically grounded DC electrical tree initiation and growth are more difficult and less harmful than the AC electrical tree. Periodically grounded DC electrical tree initiation of commercial DC cable XLPE is more difficult and the tree growth is much slower than that of untreated XLPE. Nano-SiO 2 /XLPE composite has significant inhibition effect on the initiation and growth of the periodically grounded DC electrical tree, its periodically grounded DC electrical tree initiation property is superior to the commercial DC cable XLPE, and its growth speed of periodically grounded DC electrical tree is between the untreated XLPE and commercial DC cable XLPE. The AC electrical tree test results indicate that: initiation voltage of AC electrical tree of nano-SiO 2 /XLPE is 13.6% higher than that of untreated XLPE, the AC tree length of nano-SiO 2 /XLPE is lower than the untreated XLPE in the early growth stage. However, the AC tree length of SiO 2 /XLPE exceeds that of untreated XLPE after a certain time of stress.

Further theoretical investigation on the reaction behaviour of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene (PE) is accomplished by density functional theory for high voltage cable insulation materials. The reaction potential energy information of the 13 reaction channels at B3LYP/6–311 + G(d,p) level are identified. These have been explored that the TAIC take part in the reaction behaviour on ground state during UV radiation cross-linking process and TAIC intra-molecular isomerization reaction itself. In addition, the results show that the effect of multiplication and acceleration for the cross-linking reaction of trimethylopropane trimethacrylate (TMPTMA) would be better than that of TAIC. It has further clarified the reasons why UV radiation cross-linking reaction of PE had been initiated by benzophenone (Bp), and the TAIC or TMPTMA needed to take part. The results obtained in the present study could directly guide both the optimization of UV radiation cross-linking PE process and the development of the insulation material of high-voltage cable in real application.

Further theoretical investigation on the reaction behaviour of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene (PE) is accomplished by density functional theory for high voltage cable insulation materials. The reaction potential energy information of the 13 reaction channels at B3LYP/6–311 + G(d,p) level are identified. These have been explored that the TAIC take part in the reaction behaviour on ground state during UV radiation cross-linking process and TAIC intra-molecular isomerization reaction itself. In addition, the results show that the effect of multiplication and acceleration for the cross-linking reaction of trimethylopropane trimethacrylate (TMPTMA) would be better than that of TAIC. It has further clarified the reasons why UV radiation cross-linking reaction of PE had been initiated by benzophenone (Bp), and the TAIC or TMPTMA needed to take part. The results obtained in the present study could directly guide both the optimization of UV radiation cross-linking PE process and the development of the insulation material of high-voltage cable in real application.

Voltage stabilizers are widely used to improve the resistance to electrical treeing degradation and breakdown of cross-linked polyethylene (XLPE) insulating materials. However, the effects of voltage stabilizers under high temperatures are not fully investigated by now, and the long-term effect of voltage stabilizers is still a concern due to its poor compatibility with polymer. In this work, the UV absorber 4-allyloxy-2-hydroxybenzophenone (AOHBP) which contains an unsaturated graftable vinyl group was demonstrated as a high-efficiency voltage stabilizer and compared with an ungraftable UV absorber as reference. Characterization by Fourier transform infrared (FTIR) spectra and differential scanning calorimetry (DSC) indicated that the AOHBP could be grafted onto the macromolecules of XLPE through radical addition reaction on the vinyl during peroxide cross-linking process. The test results of electrical tree initiation, electrical tree propagation and breakdown strength indicated that the grafted voltage stabilizer AOHBP exhibited higher efficiency than the ungrafted UV absorber and could comprehensively improve the electrical tree initiation voltage, inhibit the electrical tree propagation and improve the breakdown strength of XLPE at different temperatures. Through the electrical aging test with the longest aging time of up to 6000h, the AOHBP was confirmed to still maintain the initial effect on improving the breakdown strength after aging, which indicated that the migration and precipitation of AOHBP was restrained by the grafting reaction. The mechanism of AOHBP improving the electrical properties by scavenging high-energy electrons was analyzed by theoretical calculation based on density functional theory (DFT). It was proposed that the graftable AOHBP is a promising voltage stabilizer.

Theoretical investigation on the multiple-channel addition reactions of hydrogen in polyethylene to bismaleimide in the Ultra-violet (UV) radiation cross-linking process is accomplished by density functional theory. Their energetic information of the nineteen reaction channels at B3LYP/6-311 + G(d,p) level is obtained. Two types of electrophilic addition reaction, one is the 4-position hydrogen in 4-methylheptane to C of C=C groups in bismaleimide and the other one is the 4-position hydrogen in 4-methylheptane to O of C=O groups in bismaleimide, are identified. The effects of introducing the heteroatom O and/or the benzene ring among both ends of the two maleimide rings have been evaluated. The results show that the addition reaction potential barrier height to O in C=O groups is lower than that of the C in C=C groups in the conjugative bismaleimide system.The founding of the addition reaction channel to O in C=O groups could clear further the mechanism of grafting bismaleimide to polyethylene.

Polypyrrole (PPy) nanobowls were successfully prepared through a reactive self-degraded template polymerization and the morphology of PPy nanobowls was characterized by scanning electron microscopy (SEM). The nanobowls were uniform with diameters of about 100 nm. The low density polyethylene/polypyrrole (LDPE/PPy) nanocomposites were obtained by melt blending method. The structures of PPy nanobowls and the nanocomposites were studied by Fourier transform infrared spectrometer (FTIR). Space charge distributions in LDPE/PPy nanocomposites with different PPy nanobowls contents were measured using the pulsed electroacoustic (PEA) method. The results indicated that PPy nanobowls doping with a small quantity exhibited excellent suppression performance of space charge accumulation in LDPE and the nanocomposites showed improved direct current (DC) electrical conductivity and breakdown characteristics.

This paper employs the SAXS technique to study the microstructure evolution of nano Al2O3/low-density polyethylene (LDPE) composite film during temperature increase and decrease (including interfacial layer thickness, mass fractal and surface fractal), and discusses the deformation memory effect (DME) mechanism. Compared with the case of pure LDPE, there are some new phenomena observed in the Al2O3/LDPE composite film, such as an interfacial layer and surface fractal. The experimental results showed that, when the temperature rose from 25 °C to 180 °C, the interfacial layer thickness of the composite film increased from 2.8 nm to 3.5 nm, and the surface fractal dimension increased from 1.2 to 2.0, with the lamellar crystal of the PE molecular chains melting. When the temperature dropped from 180 °C to 30 °C, the interfacial layer thickness decreased from 3.5 nm to 3.0 nm, and the surface fractal dimension changed from 2.0 to 1.2, with the PE molecular chains recrystallizing. We found that the DME of the interface layer is that thickness and area increase when temperature rises and decrease when temperature decreases. The addition of Al2O3 nanoparticles into the polymer results in the adsorption of space charges in the matrix onto the nanoparticles and in the interfacial regions, which efficiently inhibits the space charge accumulation of the composite material in the gradient electrical field.

A new water blade electrode method is presented to accelerate water tree initiation and propagation in cross-linked polyethylene (XLPE) insulation, and the validity was verified by a series of experiments. Water tree morphology and length over time were monitored using a polarized light microscope and compared to the results through the conventional water needle electrode method. The influence of electric field distribution along the water electrodes on water tree initiation and morphology was also investigated on the basis of experimental data and finite element simulation. Furthermore, the effect of voltage frequency on water tree initiation was also investigated. It was found that the water blade electrode method could greatly accelerate water tree initiation and propagation and it was more convenient to slice XLPE for observation. The high frequency voltage could more efficiently facilitate water tree initiation and propagation.

A theoretical investigation on the mechanism of the tailored side-chain architecture of benzil-like voltage stabilizers for enhanced dielectric electrical breakdown strength of cross-linked polyethylene at the atomic and molecular levels is accomplished. The HOMO–LUMO energy gaps, the ionization potentials, and the electron affinities at the ground states of a series of benzil-like molecules are obtained at the B3LYP/6-311+G(d,p) level. The 8 isomerization reactions at the S0 state, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy paths (MEP) found using the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The substituent group effect, functional group effect, and electronic effect of the different heteroatoms (O, N, S) in substituent groups have been evaluated. The results show that benzil-like molecules, which have much smaller HOMO–LUMO energy gaps, much lower ionization potentials, and much larger electron affinities than those of aliphatic chains, can increase the electrical breakdown strength effectively as voltage stabilizers in cross-linked polyethylene. This result is consistent with Jarvid’s suggestions (Journal of Polymer Science, Part B: Polymer Physics, 2014, 52(16): 1047–1054).

Quantum chemical molecular dynamics (QM/MD) simulations based on a self-consistent charge density functional tight-binding (SCC-DFTB) method on SiO2 filler in polyethylene (PE) showed that: in the absence of SiO2, the PE was quickly charged by high-energy electrons, which resulted in C–C or C–H bonds breaking; on the contrary, in the presence of SiO2 nanoclusters, electron trapping and accumulating were dominated by SiO2 nanoclusters rather than polyethylene, which made polyethylene be preferentially protected and increased the initial time of electrical treeing. In our calculations, we also observed double electric layers around the SiO2 nanocluster, in agreement with recent suggestions from experimental observations. Furthermore, compared with some other investigated nanoclusters, SiO2 was regarded as the most promising candidate attributed to the highest electron affinity. We further observed that once the high-energy electrons were supersaturated in the nanoclusters, the polyethylene chains would be unavoidably charged and C–H bond breaking would occur, which resulted from the interaction between H and O or Si in the nanoclusters. Following that, decomposing and cross-linking of the polyethylene chains were involved in the initial growth of electrical treeing. The current observation can potentially be used in power cable insulation.

A theoretical investigation on the benzophenone-initiated UV radiation cross-linking reactions of polyethylene is accomplished at B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energies of 9 reaction channels are identified in the T1 state. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities of the polyethylene, photoinitiator, voltage stabilizer, antioxidant, and by-products in the polyethylene insulation composite products are obtained. The results show that the by-products, photoinitiator, voltage stabilizer, and antioxidant can effectively increase the electrical breakdown strength. In addition, aromatic ketone voltage stabilizer and hindered phenol antioxidants of the studied molecule can be grafted to the polyethylene chain easily during the polyethylene UV radiation cross-linking process, and they have excellent compatibility with the polymer matrix. The investigation is expected to provide reliable information for optimizing the polyethylene UV radiation cross-linking process and for the development of insulation material for high-voltage cable for use at voltages exceeding 500 kV in real applications.

Theoretical investigation of the reaction of graft maleimide to polyethylene in the UV radiation cross-linking process is accomplished at the B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energy surface of the nine reaction channels is identified. The results show that the N,N&prime, ethylenedimaleimide can connect two 4-methylheptane molecules and act as the cross-linking agent. The calculated reaction potential barrier of forming 4-methylheptane radical by maleimide is higher than that of maleic anhydride. The study is expected to provide a basis for optimizing the UV radiation cross-linking polyethylene process and development more than 500 kV high-voltage cable insulation materials in practical applications.

High voltage direct current (HVDC) cables develop rapidly due to the increased demand for renewable sources and long distance power transmission, recently. Cross-linked polyethylene (XLPE) insulated direct current (DC) cable is one of main HVDC cables. However, XLPE insulation materials incline to ageing and degradation in the long-term high temperature environment, which leads to the reduction of the electric, physicochemical and mechanical properties. In this paper, the effects of a single thermal ageing on the DC electrical conductivity of HVDC cable XLPE insulation materials were investigated in 130, 140 and 150 oC by accelerated ageing experiments in nitrogen atmosphere to simulate the pressure environment of cable insulation. The change trend and mechanism of DC electrical conductivity at different ageing temperature and time were analyzed through Fourier transform infrared (FTIR) spectra. The experiments and analysis results indicated that the electrical conductivity of XLPE insulation after thermal ageing firstly reduced and were below that of unaged XLPE, and then gradually increased during the whole ageing temperature and time range by the combined effect of thermal decomposition, post-crosslinking and the diffusion of the low molecular weight substance. The higher the thermal ageing temperature was, the greater the changes of the electrical conductivity of XLPE insulation were. Under the same ageing time of 700 h, the DC electrical conductivity of XLPE insulation at different ageing temperature followed well the Arrhenius equation. Based on data processing and analyzing, the electrical conductivity activation energies of XLPE before and after thermal ageing were obtained and it was found that the activation energies for aged XLPE insulation were superior to unaged XLPE. The thermal ageing increased the electrical conductivity activation energy. In the FTIR spectra, it can be seen that the intensity of carbonyl absorption peak at about 1722 cm−1 increased after thermal ageing. The carbonyl index has been calculated by the rate of peak near 1722 and 2020 cm−1 to evaluate the ageing degree of XLPE insulation materials. It was found that the carbonyl index of unaged XLPE was the minimum and increased as the ageing time under different thermal ageing temperature. At high thermal ageing temperature, the carbonyl index increased rapidly. The high temperature contributed to the thermal decomposition of XLPE insulation materials, which caused oxygen groups increasing in molecular chain and the increasing rate of the carbonyl was accelerated.

In this study, we performed a quantum chemical molecular dynamics (QM/MD) simulation to investigate the space charge accumulation process in copolymers of polyethylene (PE) with ethylene acrylic acid (EAA), ethylene vinyl acetate (EVA), styrene-ethylene-butadiene-styrene (SEBS), and black carbon (BC). We predicted that BC, especially branched BC, would possess the highest electron affinity and is identified as the most promising filler in power cable insulation. Following incorporations of 0-4 high-energy electrons into the composites, branched BC exhibited the highest stability and almost all electrons were trapped by it. Therefore, PE was protected efficiently and BC can be considered as an efficient filler for high voltage cables and an inhibitor of tree formation. On the contrary, although EAA, EVA, and SEBS can trap high-energy electrons, the latter can be supersaturated in composites of EAA, EVA, and SEBS with PE. The inserted polymers was unavoidably destroyed following C-H and C-O bond cleavage, which results from the interactions and charge transfer between PE and inserted polymers. The content effects of -COOH, benzene, and -OCOCH3 groups on the electron trapping, mobility and stability of PE were also investigated systematically. We hope this knowledge gained from this work will be helpful in understanding the role of inserted polymers and the growth mechanisms of electrical treeing in high voltage cable insulation.

The key bond lengths and angles for reactants, transition states and products on the H immigration reaction pathways for neutral and ionic states.

In this work, the energy gaps (Eg) of highest occupied orbitals and lowest unoccupied orbitals, trap energies (Et(e) and Et(h)) and excited energies of polyethylene model compound, typical defect compound, acetophonene, and 33 designed additives are obtained using density functional method at B3LYP/6–311+G(d, p) level. The correlation between trapping-electrons (holes) abilities of additives and molecular frontier orbitals is established, and a new understanding for trap mechanism based on chemical molecular orbital levels is given for the first time which could be used to filter qualitative additives as voltage stabilizers of polyethylene. The role of trap energies and the energy gaps on discussing space charge accumulation and electric breakdown is analyzed in detail. A molecular design strategy for potential additives of cross-linked polyethylene insulated high-voltage cable is shown based on conjugation effect, substituents character, and polycyclic aromatic compounds. © 2015 Wiley Periodicals, Inc.

A theoretical investigation on the mechanisms of acetophenone added to polyethylene as voltage stabilizers is accomplished at the atomic and molecular levels. The five reaction pathways of valence bond isomerization of acetophenone have been elucidated. The electronic structures at the ground states and lowest triplet states of acetophenone and its valence bond isomers were calculated at the B3LYP/6-311+G(d,p) level. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities at the ground states of studied molecules were obtained at the same level. The theoretical results are in good agreement with the available experimental findings. Our calculations indicate that the valence bond isomerization forming the Huckel structure is the major pathway, and the other valence bond isomerizations that yield Dewar, Ladenburg, and Bicyclopropylene acetophenones are minor pathways. Based on these results, several interesting voltage stabilizers have been designed.

The (Fe@FexOy)/epoxy resin (ER) composites are fabricated and their dielectric and magnetic properties are systematically investigated in order to acquire the high-performance electromagnetic insulating materials. Fe@FexOy nanoparticles with core–shell structure are prepared using an oxidation process. The thickness of FexOy shell and soft magnetic properties of Fe@FexOy nanoparticles can be controlled by adjusting the oxidizing temperature (Tox). The FexOy shell benefits the reduction of eddy current and the improvement of breakdown strength in their ER composites. With increasing Tox, the dielectric constant of the composites increases because of the enhancement of duplex interfacial polarization. Besides, the real part of the complex magnetic permeability has a slight decrease, which might be due to the more domain wall movement. 2015 Published by Elsevier Ltd.

Ag nanoparticles@polydopamine (AgNPs@PDA) core–shell particles were prepared by one-step oxidative–reductive reaction, which Ag+ was used as oxidant and dopamine as reducing agent. The dopamine was polymerized to PDA surface and shielded the Ag nanoparticles. The AgNPs@PDA particles were used as fillers and introduced into poly(vinylidene difluoride) (PVDF) to prepare the AgNPs@PDA/PVDF dielectric composites. AgNPs were introduced aiming to increase the dielectric constant of the composites and PDA was employed to improve the compatibility between fillers and polymer. The morphology and the dielectric properties of the AgNPs@PDA/PVDF composite films were thoroughly investigated. The influencing factors to the dielectric performances of the composites were studied, including the ratio of AgNO3 and dopamine, pH values of the preparing solution and the fraction of the fillers. The highest dielectric constant of the AgNPs@PDA/PVDF composites was about 53 when the content of fillers was 25 wt.% at 100 Hz. The percolation threshold of the composites was predicted at about 25.5 wt.%.

Herein a diaphragm type dielectric elastomer actuator by blending azobenzene dyes into a polyurethane matrix (Azo/PU) is described. The effects of azobenzene content on the dielectric, mechanical, and electromechanical properties of the Azo/PU blends are discussed. The resultant blends with azobenzene content ranging from 1 to 8 wt% were characterized. The dielectric permittivity of PU increased from 8.0 to 11.1 (increasing of 38.5%) at 1 wt% azo content and reached a maximum of 35.6 (increasing of 343%) at 4 wt% azo content. By blending with a small content of azo the dielectric breakdown strength reached 57 kV mm−1, which is 86% higher than that of the neat PU. The 30 μm thick diaphragm of Azo/PU blend with 1 wt% azo content exhibited the highest actuated displacement at the center around 700 μm. Meanwhile the neat PU gave a displacement of 25 μm. That is a 26-fold increase in actuation is obtained by blending only 1 wt% azo dyes into the PU matrix. Infrared spectroscopy was used to characterize the structure of the Azo/PU blends. The particular chemical structure the Azo/PU blend containing 1 wt% of azo dyes is proposed to be responsible for the improvement in electromechanical actuation.

Theoretical investigation on the radical-initiated reactions of the polyethylene cross-linking process with the voltage stabilizer grafting is accomplished by density functional theory (DFT) calculations. At the B3LYP/6-311+G(d,p) level, the molecular properties of 22 reactions and reaction potential energy information of 18 radical-initiated reactions are obtained. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities of the cross-linking agent, voltage stabilizer, antioxidant, and by-product in the polyethylene insulation composite are calculated. The results show that the by-product, cross-linking agent, and voltage stabilizer can effectively increase the electrical breakdown strength. In addition, aromatic ketone voltage stabilizer and hindered phenol antioxidants of the studied molecule can be grafted to polyethylene chain easily during the polyethylene cross-linking process, and they have excellent compatibility with polymers matrix. The investigation is expected to provide reliable information for optimizing process and for the development of the insulation material of high-voltage cable exceed 500 kV in real applications.

A theoretical investigation on the dielectric insulation mechanism of sulfur hexafluoride(SF6) and its potential alternative gases at the atomic and molecular levels was made. The electronic structures of the molecules of them were calculated at the B3LYP/6-311+G(d,p) level. The HOMO-LUMO energy gaps, ionization potentials, electron affinities, and dipole moments of the studied molecules at the ground state were obtained. The 11 isomerization reactions, with the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path by the intrinsic reaction coordinate theory, were also obtained at the same level. The results show that the insulation gas, with the larger HOMO-LUMO energy gap, the higher ionization potential and the stronger electron affinity, can increase the dielectric breakdown strength efficiently, which is in good agreement with the available experimental finding. We suggested that the molecule with isomerization reaction occurring can dissipate the energy of hot electrons availably, which is favorable to the dielectric breakdown strength increasing for the SF6 potential alternative gas.

A theoretical investigation is completed on the mechanism of electrical breakdown strength increment of polyethylene. It is shown that it is one of the most important factors for increasing electrical breakdown strength of polyethylene through keto-enol isomerization of acetophenone and its analogues at the ground state S0 and the lowest triplet state T1. The minimum structures and transition states of the keto- and the enol-tautomer of acetophenone and its analogues at the S0 and T1 states are obtained at the B3LYP/6-311+G(d,p) level, as well as the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory at the same level. The two C-C bond cleavage reaction channels have been identified in acetophenone. The calculated results show that the energy barriers of keto-enol isomerization of acetophenone and its analogues at S0 and T1 states are much smaller than the average C-C bond energy of polyethylene, and the acetophenone doping or bond linked into polyethylene can increase the electrical breakdown strength and inhibit polyethylene electrical tree initiation and aging.

The doping effect of graphene nanoplatelets (GNPs) on electrical insulation properties of polyethylene (PE) was studied by combining experimental and theoretical methods. The electric conduction properties and trap characteristics were tested for pure PE and PE/GNPs composites by using a direct measurement method and a thermal stimulated current (TSC) method. It was found that doping smaller GNPs is more beneficial to decrease the conductivity of PE/GNPs. The PE/GNPs composite with smaller size GNPs mainly introduces deep energy traps, while with increasing GNPs size, besides deep energy traps, shallow energy traps are also introduced. These results were also confirmed by density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method calculations. Therefore, doping small size GNPs is favorable for trapping charge carriers and enhancing insulation ability, which is suggested as an effective strategy in exploring powerful insulation materials.

The role of a series of functionalized graphene additives in power cable insulation in suppressing the growth of electrical treeing and preventing the degradation of the polymer matrix has been investigated by density functional theory calculations. Bader charge analysis indicates that pristine, doped or defect graphene could effectively capture hot electrons to block their attack on cross-linked polyethylene (XLPE) because of the π–π conjugated unsaturated structures. Further exploration of the electronic properties in the interfacial region between the additives and XLPE shows that N-doped single-vacancy graphene, graphene oxide and B-, N-, Si- or P-doped graphene oxide have relatively strong physical interaction with XLPE to restrict its mobility and rather weak chemical activity to prevent the cleavage of the C–H or C–C bond, suggesting that they are all potential candidates as effective additives. The understanding of the features of functionalized graphene additives in trapping electrons and interfacial interaction will assist in the screening of promising additives as voltage stabilizers in power cables.

PEGylation of peptide drugs prolongs their circulating lifetimes in plasma. However, PEGylation can produce a decrease in the in vitro bioactivity. Longer poly(ethylene glycol) (PEG) chains are favourable for circulating lifetimes but unfavourable for in vitro bioactivities. In order to circumvent the conflicting effects of PEG length, a hydrophobic peptide, using an antimicrobial peptide as a model, was PEGylated with short PEG chains. The PEGylated peptides self-assembled in aqueous solution into micelles with PEG shell and peptide core. In these micelles, the core peptides were protected by the shell, thus reducing proteolytic degradation. Meanwhile, most of the in vitro antimicrobial activities still remained due to the short PEG chain attached. The stabilities of the PEGylated peptides were much higher than that of the unPEGylated peptides in the presence of chymotrypsin and serum. The antimicrobial activities of the PEGylated peptides in the presence of serum, an ex vivo assay, were much higher than that of the unPEGylated peptide.

With the wide application of high voltage and ultra-high voltage cross-linked polyethylene (XLPE) insulated cables and the increasing demand for operation stability, development of XLPE insulation materials with high dielectric strength has become one of the most popular research topics in recent years. In this paper, acetophenone/polyethylene (PE) composites with different contents of acetophenone are fabricated with the melt blending method in torque rheometer. The AC and DC dielectric breakdown strengths of PE and acetophenone/PE composites are tested at room temperature. A theoretical calculation is performed at the B3LYP/6-311+G (d, p) level to investigate the energy barrier variation of keto-enol tautomerism of acetophenone. The experimental results show that the AC and DC breakdown strengths can be increased by 48.5% and 30.4% respectively when an appropriate amount of acetophenone is added into PE. This is because the potential energies of keto-enol tautomerism of acetophenone are lower than the average C-C bond energy of PE. As a result, the energy of hot electrons can be dissipated by this reaction without causing any rupture of PE molecular chains, thus significantly improving the breakdown strength of PE. Addition of acetophenone derivatives with specific functional groups is a promising method to develop high-performance XLPE insulation materials for high-voltage AC and DC cables.

The design and manufacture of XLPE insulation HVDC cable joint is a challenge because the internal electric field distribution of the joint insulation can be affected by several factors and therefore is difficult to do accurate calculation. In this paper, the electric field distribution of cable joint fabricated with different silicone rubbers as reinforced insulation is calculated using COMSOL Multiphysics simulation. The influence of electrical conductivities of insulating materials on the electrical field distribution is investigated. The research results show that the electric field stress is unacceptably high in specific area if the joint is fabricated with common silicon rubber as insulation reinforcement. When the nonlinear conductive silicon rubber is used as reinforcing insulation for cable joint stress control cone, the electric field distribution profile becomes more uniform, and the maximum field strength locates inside the cable insulation layer. It is expected to achieve good performance XLPE HVDC cable joint by using nonlinear conductive silicon rubber for stress control cone insulation.

With the bulge of electrical load for big cities, acceleration of island exploitation strategy and rapid development of renewable energy power generation, the development and application of flexible direct current (DC) power transmission have become an inexorable trend. As a major carrier of flexible DC power transmission, cross-linked polyethylene (XLPE) insulated high voltage direct current (HVDC) cables become more and more important in recent years due to their light weight, good electrical and thermal performance, simple manufacturing process, convenient installation and maintenance in combination with non environmental pollution. The aging of XLPE insulation usually occurs under the effects of such factors as electricity, heat, oxygen, humidity, mechanical stresses, light, chemicals and microorganism encountered in service. It can lead to irreversible damage of XLPE insulation materials, even power accidents, which may bring hidden danger to the operation of power network. In this paper, a comprehensive review is presented on the worldwide research and development related to the aging of XLPE insulation in HVDC cables. The principal factors and mechanisms causing the aging of DC XLPE insulation are also introduced together with the inhibition methods of space charge, which is one of the major components of the aging process in XLPE insulation.

The semi conductive shield material was prepared by mixing a variety of copolymer and carbon black (CB) with LDPE by melt blending method. In order to study the suppression of semi-conductive shield materials on space charge injection, inorganic nano fillers with different properties were added respectively, and the space charge distribution of double-layer sample which was composed of a semi conductive shield layer and a XPLE insulation layer was measured by using pulse electro-acoustic (PEA) method. The results indicate that when various semiconductive shield materials are used, the space charge distributions of XLPE are different. Moreover, the space charge injection from the surface of XLPE can be suppressed by adding nano-MgO and nano-SiC into semi-conductive shield materials.

The electric field distributions in high voltage direct current cable termination are investigated with silicone rubber nanocomposite being the electric stress control insulator. The nanocomposite is composed of silicone rubber, nanoscale carbon black and graphitic carbon. The experimental results show that the physical parameters of the nanocomposite, such as thermal activation energy and nonlinearity-relevant coefficient, can be manipulated by varying the proportion of the nanoscale fillers. The numerical simulation shows that safe electric field distribution calls for certain parametric region of the thermal activation energy and nonlinearity-relevant coefficient. Outside the safe parametric region, local maximum of electric field strength around the stress cone appears in the termination insulator, enhancing the breakdown of the cable termination. In the presence of the temperature gradient, thermal activation energy and nonlinearity-relevant coefficient work as complementary factors to produce a reasonable electric field distribution. The field maximum in the termination insulator show complicate variation in the transient processes. The stationary field distribution favors the increase of the nonlinearity-relevant coefficient; for the transient field distribution in the process of negative lighting impulse, however, an optimized value of the nonlinearity-relevant coefficient is necessary to equalize the electric field in the termination.

Cyanoketene (OCCHCN) has been reported as a potential alternative insulation gas for SF6 in Patent US0135817. Stationary point equilibrium geometries on the ground state have been optimized at the B3LYP/6-311+G(d,p) level, and the harmonic vibration frequencies are calculated at the same level. The HOMO-LUMO energy gaps (Eg), ionization potentials (IP), and electron affinities (EA) of the studied molecules are obtained. The minimum energy path (MEP) is obtained by the intrinsic reaction coordinate (IRC) theory, and the energetic information is further refined by QCISD(T) (single-point) method. The results show that OCCHCN can be used as SF6 alternative insulation gas in high voltage equipment according to potential energy surface analysis. As the isomerization and the cleavage reactions potential barriers are lower than the Eg and IP values, resulting in OCCHCN is not easy to be ionized and excited.

In order to improve the DC dielectric properties of cross-linked polyethylene (XLPE) insulation materials, carbon black (CB)/ XLPE nanocomposites were prepared with the melt blending method. The pulsed electro-acoustic (PEA) method was used to measure the space charge distribution of XLPE and CB/XLPE nanocomposites. The relationship between the DC electrical conduction and the applied electric field strength of each material was measured under several constant temperatures. The research results show that the amount of space charges significantly reduces when a small quantity of CB was added into XLPE. The ability of composites to inhibit space charges is strong when the CB content is 1 phr. It was found that the electrically conductive properties of XLPE present nonlinear characteristics under lower electrical field intensity. The electrical conductivity significantly increases with temperature. The electrical conductivity of the nanocomposites with CB is almost a constant value under the electrical field below 20 kV/mm, and the effect of temperature on the DC electrical conductivity obviously decreases, when temperature goes up. The addition o CB into the XLPE can effectively inhibit the internal space charge accumulation and improve the DC conduction characteristics of the composites.

A theoretical investigation on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels is accomplished. The addition of aromatic carbonyl and carboxyl compounds as voltage stabilizers may increase the electrical breakdown strength of polyethylene. The HOMO-LUMO energy gaps, the ionization potentials, the electron affinities, and the reorganization energies at the ground states of a series of aromatic carbonyl and carboxyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The 24 isomerization reactions at the S0 and T1 states, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The results show that 4,4'-didodecyloxybenzil (Bd) molecule, which has much smaller HOMO-LUMO energy gap, much larger reorganization energy than others, and excellent compatibility with polymers matrix, can increase the electrical breakdown strength effectively. This result is in good agreement with the available experimental findings.

A theoretical investigation is accomplished on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels. It is found that the addition of aromatic carbonyl compounds as voltage stabilizers is one of the important factors for increasing electrical breakdown strength of polyethylene, as the additives can trap hot electrons, obtain energy of hot electrons, and transform the aliphatic cation to relatively stable aromatic cation to prevent the degradation of the polyethylene matrix. The HOMO-LUMO energy gaps (E(g)), the ionization potentials (IPs), and electron affinities (EAs) at the ground states of a series of aromatic carbonyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The theoretical results are in good agreement with the available experimental findings, show that 2,4-dioctyloxybenzophenone (Bzo) and 4,4'-didodecyloxybenzil (Bd) molecules can effectively increase the electrical breakdown strength when they are doped into polyethylene because of their much smaller E g values than all the other studied aromatic carbonyl molecules and excellent compatibility with polymers matrix.