Search

To explore the microscopic mechanism of thermal stability of oil-paper insulation， a molecular model consistent with the actual oil-paper insulation is established. Through comparison with the experimental results， the effectiveness of the model is verified. With temperature as an independent variable， variation of the mechanical parameters and hydrogen bond energy of the cellulose molecular model under the action of a thermal field is investigated. The results show that parameters characterizing the mechanical properties of cellulose， such as bulk modulus （K）， Young's modulus （E）， shear modulus （G）， and Poisson's ratio （v） of the cellulose crystalline zone model are larger than those of the amorphous zone model at the same temperature， and the distribution of hydrogen bond energy remains the same. Thus， the cellulose crystalline zone is superior to the amorphous zone in mechanical properties and determines the insulation properties of cellulose insulating paper. The results of the study provide a theoretical basis and method for investigating the microscopic mechanism of thermal aging of oil-paper insulation.

Oil-impregnated paper is the most widely used insulating material for power transformers. Power transformers inevitably generate a lot of heat during operation. Among them, thermal aging is one of the main forms of aging for insulating paper. In this study, the ab initio molecular dynamics method based on the density functional theory is used to simulate the cracking mechanism of cellobiose under transient high temperature. The results show that the cellobiose is relatively stable at 343 K, the motility of the cellobiose is enhanced at 1,800 K, the cellobiose starts to decompose at 2,400 K, and new characteristic products are formed at 3,000 K. The characteristic products include CO, H2O, CH3OH, H2, and CH4. These characteristic products can represent the degree of cracking of insulating paper. Therefore, it is necessary to explore the mechanism of cracking of insulating paper caused by transient high temperature.

In order to reveal the migration and evolution of gas molecules in the actual oil–paper insulation composite system of transformer from the molecular level, the diffusion behavior of seven gas molecules (H2, CO, CO2, CH4, C2H2, C2H4, C2H6) generated during the operation and aging of oil-immersed transformers in the oil–paper composite insulation system is studied by molecular dynamics. Firstly, based on the molecular dynamics software, the model of the oil–paper composite insulation system and the gas molecule model is constructed. In order to compare and analyze the diffusion properties of gas molecules in a single medium, a single model of insulating oil and cellulose is also constructed. Then, the diffusion coefficients of gas molecules in the insulating oil, cellulose, and oil–paper insulating composite system are simulated and calculated. And the differences in the diffusion properties of gas molecules in the three insulating mediums are discussed. Finally, the microscopic mechanism of diffusion of different gas molecules in the three mediums is analyzed. The simulation results show that among the three mediums, the diffusion coefficient of H2 is the largest, while the diffusion coefficients of the other gas molecules are not very different. The diffusion coefficients of the seven gas molecules are the smallest in the oil-immersed paper composite insulation system, followed by cellulose, while the diffusion coefficients are the largest in mineral oil. It indicates that the diffusion of gas molecules is inhibited in oil–paper insulation systems where the insulating paper is completely immersed in oil. This is mainly due to the fact that the insulating oil completely penetrates into the paper, filling the pores and voids between the fibers, resulting in a reduction in the transition vacancies of the intermediate gas molecules, which hinders the diffusion of the gas molecules. [ABSTRACT FROM AUTHOR]

The growing concern for environmental sustainability has created an urgent need for the development of innovative and environmentally friendly packaging materials. Among the various options available, clay-starch nanocomposites have emerged as a promising avenue for improving the barrier properties and mechanical strength of paper substrates. In this scientific paper the importance of clay-starch nanocomposite coatings on paper substrate and highlight the role of computer simulations, especially molecular dynamics, in elucidating their structural and functional properties. It has been shown that phyllosilicates with a layer charge < 0.4 electrons per stoichiometric unit can intercalate starch in the interlayer space, forming a barrier for water vapor in the covering layer. Phyllosilicates with a shell charge of > 0.4 electrons per stoichiometric unit were not able to intercalate starch. Thus, clay-starchnanocomposites can provide limited water vapor transfer rates and can be recommended asa promising material for dry food packaging.

A thermal stability analysis method of meta-aramid insulating paper based on computer molecular dynamics technology is designed in this paper. First, the raw materials and equipment for preparing meta-aramid insulating paper were determined to prepare meta-aramid insulating paper. Then, the internal structure and morphology of meta-aramid insulating paper are analyzed for the subsequent stability analysis. Finally, the basic principle of computer molecular dynamics technology is analyzed, which is used to analyze the thermal stability of meta-aramid insulating paper, mainly from the stability of its crystal region. The experimental results show that the proposed method is effective and feasible in analyzing the thermal stability of aramid insulating paper between samples. [ABSTRACT FROM AUTHOR]

A transparent, bendable, high oxygen barrier cellulose‐based film was prepared, which has far better oxygen barrier properties than conventional polyethylene, polypropylene and cellophane materials. A series of regenerated cellulose films (RCs) were prepared from filter paper lacking oxygen barrier properties under different cellulose concentrations and gelation times. It was shown that the cellulose concentration and gel time had a greater effect on the oxygen barrier properties of RCs. When the cellulose concentration was 4 wt% and the gel time was 3 h, the RCs obtained the lowest oxygen permeability coefficient (OPC) down to 2.21 × 10−17 cm3 cm cm−2 s−1 Pa−1. The films have a tensile strength of 109.5 MPa, an elongation at break of 27.3% and a light transmission rate of 89%. In further, molecular dynamics simulations showed that when the filter paper was converted to RCs, the increase in hydrogen bonding and the decrease in free volume between cellulose chains caused a decrease in the diffusion coefficient of oxygen. As a novel biobased high oxygen barrier material, the film has broad application prospect in packaging and chemical industry. [ABSTRACT FROM AUTHOR]

Nano-modified insulating paper, due to its outstanding performance, is regarded as a promising material in power system. Accordingly, in this study, three different kinds of polysilsesquioxane (POSS) nanoparticles were prepared from silsesquioxane monomers with octaaminophenyl, octaphenyl, or octamethyl substituents and used to prepare modified cellulose insulating paper. Doping with the POSS nanoparticles effectively improved the tensile strength of the insulating paper and reduced its relative dielectric constant. Specifically, doping with octaaminophenyl-POSS (OAPS) nanoparticles at 10 wt% showed the optimal modification effect. Accelerated thermal aging was carried out on this OAPS-modified insulating paper. Compared with those of the unmodified sample, the tensile strength of the modified sample was 16.87% higher and the relative dielectric constant was 24.63% lower after aging at 130 °C for 31 days. Molecular dynamics simulation was used to study the mechanism by which OAPS improves the tensile strength, dielectric properties, and thermal stability of cellulose insulating paper, and the results indicated that it forms hydrogen bonds with the cellulose chains, inhibiting their movement and inhibiting system polarizability. [ABSTRACT FROM AUTHOR]

To enhance the thermal–mechanical properties of insulating paper, nano-fibrillated cellulose (NFC) was used to dope cellulose. The mechanical strength and thermal stability of cellulose insulating paper with different NFC doping mass fractions were analyzed by molecular dynamics simulations and experiments, and the optimal doping ratio of NFC was determined. The results showed that the mechanical properties, thermal conductivity, thermogravimetric properties, and glass transition temperature of NFC-modified insulating paper were improved compared with ordinary insulating paper. Among them, the maximum tensile strength after doping was 58.147 MPa, which was 20.040 MPa higher than the 30.107 MPa of the insulating paper before modification. The glass transition temperature was also 8.54 °C higher than the 127.05 °C before modification. Meanwhile, the mechanism of NFC doping enhancement on the insulating paper's thermal–mechanical properties was analyzed from the aspects of cohesive energy density, fractional free volume, hydrogen bond, and mean square displacement. We believed that the doping of NFC can improve the thermal–mechanical properties of the insulating paper because it could enhance cellulose's interchain force, fill the insulating paper's internal pores, and increase the hydrogen bonding energy. The thermal–mechanical properties of cellulose insulating paper with different NFC doping mass fractions were analyzed to determine the optimal doping ratio of NFC through molecular dynamics simulations and experiments. Meanwhile, the mechanism of NFC doping enhancement on the insulating paper's thermal–mechanical properties was also investigated from the aspects of cohesive energy density, free volume fraction, hydrogen bonding, and mean square displacement. [ABSTRACT FROM AUTHOR]

The regular operation of transformers is significantly impacted by the insulation effectiveness of the transformer insulation oil–paper. In order to explore the mechanism of the influence of an electric field on the thermal decomposition performance of insulating oil–paper, this paper simulated the process of electrothermal coupling decomposition of insulating oil–paper from the micro-level based on molecular dynamics. It was determined that the insulating oil is made up of three 16-carbon hydrocarbon molecules, while the insulating paper is made up of 30 fibrous disaccharide molecules. Using the molecular dynamics simulation approach, the pyrolysis of the insulating oil and insulating paper under various electric field strengths was simulated, and the lysis of reactants and the distribution of products were statistically examined. This paper also studied how the electric field affected the microscopic process of the insulating oil–paper pyrolysis. The findings demonstrate that under the influence of electrothermal coupling, the big molecules of the insulating oil and insulating paper are pyrolyzed to produce a variety of tiny molecules. For the insulating oil, it is easily subject to electron displacement polarization under the influence of an external electric field since it contains non-polar molecules, especially impacted by an electric field of 100 V/m. For the insulating paper, its polar nature, on the other hand, makes itself a good candidate for guiding polarization when exposed to an external electric field. So, the greater the electric field strength is, the greater the impact on the thermal decomposition of the insulating paper is. [ABSTRACT FROM AUTHOR]

The complex and demanding environments of high humidity, heat, altitude, and intricate electric fields necessitate higher standards for the mechanical, thermal stability, and electric insulation properties of insulating paper. However, a single nanomaterial alone struggles to enhance overall performance. Hence, we propose employing two-phase nanomaterials with distinct dimensions to synergistically enhance the performance of cellulose insulation paper. Accordingly, "simulation design directly guided experimental research" was utilized in constructing nano-BN/nanocellulose/cellulose (nano-BN/NFC/cellulose) models through molecular dynamics simulation, and its mechanical parameters, dielectric properties, thermal stability, and so on were simulated and calculated. Based on simulation results, suitable proportions of nano-BN/NFC/cellulose insulating paper were prepared. Nano-BN and NFC synergistically enhance the mechanical properties of insulating paper. The nano-BN, CNF, and cellulose are arranged layer by layer under the action of gravity, allowing the fillers to overlap diagonally along the plane, synergistically forming a thermally conductive network conducive to heat transfer. Additionally, a strong interfacial effect is formed between the three-phase materials, reducing the overall structure's polarization effect and charge accumulation, and synergistically enhancing electrical insulation performance. The 12%nano-BN/NFC/cellulose (P12) exhibits optimal overall performance and is expected to be used in power equipment operating in special environments with high humidity and heat. [Display omitted] • The results of MD simulations successfully guided the preparation of nano-BN/NFC/cellulose insulating paper. • Nano-BN and NFC synergistically enhance the mechanical, thermal, and electrical properties of cellulose insulating papers. • The P12 insulating paper possesses a high thermal conductivity of 0.286 W/(m·K) and a T g of 140.2 °C. • The P12 with high tensile stress (68.93 MPa), volume resistivity (4.79 × 1015 Ω m), and breakdown strength (67.48 kV mm−1). [ABSTRACT FROM AUTHOR]

Epoxy-impregnated aramid composites, notable for their excellent mechanical and insulation qualities, are pivotal in electrical engineering and electronics. However, their performance is severely restrained by interface issues. This research proposes an effective modification strategy for improving interface property by employing non-thermal atmospheric plasma to introduce active functional groups onto aramid paper. The modified composites demonstrated a 26 % increase in tensile strength and a 20 % enhancement in breakdown strength at best, alongside inhibited charge transport properties and reduced partial discharge under operational electric fields. Molecular simulation suggests that plasma treatment bolsters interface hydrogen bonding, restricting the chain mobility of the resin molecular, and thus augmenting inter-phase compatibility. This study offers a factual perspective on improving resin-impregnated composites, laying a theoretical foundation for advancing high-performance materials in power industries. [Display omitted] [ABSTRACT FROM AUTHOR]

Reducing the dielectric constant of insulating paper to improve the dielectric coordination performance of the oil‐paper systems has always been the research hotspot in the transformer insulation material industry. This paper prepares a novel poly‐p‐phenylene terephthalamide (PPTA)/cellulose composite paper with low dielectric constant and good mechanical properties. Various PPTA/cellulose mixing structures were established and the dielectric and mechanical properties were simulated via molecular dynamics simulation. Results showed that the PPTA/cellulose composite system had a lower dielectric constant than the cellulose system, for adding PPTA molecular could reduce the free volume of the system and limit the steering polarization of the dipole, as well as decrease the system polarization intensity. Constructing a three‐layer structure that contains continuous cellulose middle layer could improve the mechanical properties of the composite system greatly. Experimental results verified the simulation results. The dielectric constant of the three‐layer PPTA/cellulose composite paper decreased from 3.98 to 3.49 at 50 Hz, compared to the conventional cellulose paper. Moreover, the tensile strength of the novel three‐layer PPTA/cellulose composite paper (thickness: 130 μm) has reached 9.02 kN/m, increased by 27.6% than the directly mixed composite paper. Molecular dynamics simulation proves to be a promising method for guiding paper modification. Constructing three‐layer PPTA/cellulose structure represents an effective way to prepare a low dielectric constant composite insulating paper with good mechanical properties. [ABSTRACT FROM AUTHOR]

The diffusion of moisture in the meta-aramid fiber (PMIA) oil-paper insulation system and the thermal decomposition of PMIA insulation paper in different moisture contents were studied via molecular dynamics simulations. The results showed that the PMIA insulation paper had a stronger ability to absorb water molecules than the insulating oil; therefore, water molecules in the insulating oil diffuse to the insulation paper, which further affects the thermal decomposition of the PMIA insulation paper. The activation energy of the water-bearing composite model was 129.96 kJ/mol, which was 5.5% lower than that of the pure PMIA (137.61 kJ/mol). It indicated that moisture could promote PMIA decomposition. The micromechanism of the enhanced thermal decomposition of PMIA with moisture contents could be described as follows: The O–H bond of the water can easily break to generate H atoms and hydroxyl radicals (•OH). The strong activity of H atoms allows it to easily combine with the ammonia base at the end of PMIA to generate NH3. Additionally, the free •OH radical can easily combine with the amido and carbonyl bonds at two ends of PMIA, undergo an oxidation reaction, and generate an oxhydryl. Therefore, it can reduce the chemical stability of the PMIA chain and further drive thermal decomposition. Statistical data on fragments generated by the thermal decomposition of the water-bearing PMIA composite system show that the main products include H2, C/H/O-containing molecules, hydrocarbon molecules, N-bearing molecules, and free radicals. [ABSTRACT FROM AUTHOR]

Cellulosic insulation paper is usually used in oil-immersed transformer insulation systems. In this study, the molecular dynamics method based on reaction force field (ReaxFF) was used to simulate the pyrolysis process of a cellobiose molecular model. Through a series of ReaxFF- Molecular Dynamics (MD) simulations, the generation path of ethanol at the atomic level was studied. Because the molecular system has hydrogen bonding, force-bias Monte Carlo (fbMC) is mixed into ReaxFF to reduce the cost of calculation by reducing the sampled data. In order to ensure the reliability of the simulation, a model composed of 20 cellobioses and a model composed of 40 cellobioses were respectively established for repeated simulation in the range of 500−3000 K. The results show that insulating paper produced ethanol at extreme thermal fault, and the intermediate product of vinyl alcohol is the key to the aging process. It is also basically consistent with others’ previous experiment results. So it can provide an effective reference for the use of ethanol as an indicator to evaluate the aging condition of transformers.

With the further development of the transmission and distribution network, the requirements for the insulating system of power equipment are further deepened. As one of the important factors, insulating paper is of great value to improve its performance. The pure cellulose model and trapezoidal polyphenylsesquisiloxane (T‐PPSQ) composite model are established to analyze the mechanical and thermal properties of insulating paper cellulose. The effects of T‐PPSQ doping at different temperature on properties of cellulose are investigated by comparing the radial distribution function, mechanical parameters, glass transition temperature, mean square displacement (MSD), and free volume fraction (FVF) through molecular dynamics method. The results show that T‐PPSQ can improve the ability of cellulose to resist shear stress at different temperatures, showing good mechanical properties. When the temperature is 423 K, the mechanical performance parameters elastic modulus, bulk modulus and shear modulus can be increased by 47.2%, 18.2%, and 38.56% at most. The glass transition temperature of the insulating paper cellulose with T‐PPSQ increases by 64 K, the MSD and the FVF all decrease at different temperature which demonstrated it has improved thermal stability. The research in this paper is of great significance for improving the life of the insulating system of power equipment. [ABSTRACT FROM AUTHOR]

The paper/oil system is the main component of transformer insulation. Indicator plays a vital role in assessing the aging condition of local hot spots of transformer insulation paper. The cellulosic insulating paper is mainly composed of cellobiose. This study uses the molecular dynamics method based on reactive force field (ReaxFF) to pyrolyze the insulating paper. Various production paths of ethanol were studied at the atomic level through ReaxFF simulations. A model consisting of 40 cellobioses was established for repeated simulation at 500 K–3000 K. Besides, to explore the relationship between the intermediate products and ethanol, the combination model of intermediate products (levoglucosan, acetaldehyde, 2,2-dihydroxyacetaldehyde) was established for repeated simulation. The simulation results showed that the increase in temperature can accelerate the production of ethanol from insulating paper and its pyrolysis intermediate products, which matched the related experimental results. This study can provide an effective reference for the use of ethanol as an indicator to assess the aging condition of the local hot spots of transformers. [ABSTRACT FROM AUTHOR]

The generation and distribution of furfural are significantly affected by moisture content in the insulating paper. However, the diffusion mechanism of furfural under moisture effect is not clear, hence, this study investigates the effect of moisture on the diffusion characteristics of furfural by combining macro experiment and micro molecular dynamics simulation. The simulation results demonstrate that the increased moisture content in paper accelerates the diffusion of furfural from paper to oil, which is also proved by the experimental data. Then, the results of interaction energy analysis indicate that the increase of moisture enhances the van der Waals force between oil and furfural. The present findings are expected to improve the theoretical level of furfural analysis, which will facilitate the aging evaluation of the transformer insulating paper based on furfural. [ABSTRACT FROM AUTHOR]

For the first time, molecular dynamics simulation was used to analyse the solubility of five kinds of nanoparticles (SiO2, ZnO, Al2O3, Fe2O3, TiO2), cellulose crystalline region and cellulose molecules in this paper. The results show that the solubility of cellulose nanoparticles is positively related to the number of –OH groups on the surface of nanoparticles. The solubility between nano particles and cellulose molecules is smaller than that between cellulose crystalline region and cellulose molecules, which leads to the direct introduction of nano particles for physical modification reducing the solubility parameters of insulating paper. Through the analysis of mechanical properties, thermal stability and insulation properties, it is concluded that the comprehensive performance of the model with 70% crystalline region ratio is the best. The proportion of crystalline region further increased, the improvement of thermal stability is not obvious; the relative permittivity and the content of crystalline region are in line with the binomial fitting curve, and the constant term in the fitting curve is the relative permittivity of the amorphous region model; increasing the proportion of crystalline region is beneficial to improve the insulation performance of cellulose insulation paper. [ABSTRACT FROM AUTHOR]

This work constructed chiral nanozymes (Cys@Au/Fe Hops) with high enantioselectivity activity by cysteine-induced synthesis. The nanozymes, proficient in detecting DOPA enantiomers, have been transformed into a test paper sensor, offering enantioselective catalysis and enabling visual chiral detection via a smartphone platform. [Display omitted] • The Chiral Cys@Au/Fe Hops was synthesized using a one-pot method with cysteine as a chiral inducer. • Remarkable enantioselective catalytic activity for DOPA enantiomers by L/D -Cys@Au/Fe Hops. • Steric effects on DOPA enantiomers catalyzed by L/D -Cys@Au/Fe Hops revealed through molecular dynamics simulations. • Development of chiral nanozymes into stable test paper sensor for visual DOPA detection. The development of enantioselective nanozymes holds profound significance in synthesizing chiral compounds and elevating analytical precision. Herein, we have synthesized chiral gold/iron hierarchically organized particles (Cys@Au/Fe Hops) possessing peroxidase-like catalytic activity, through a one-pot method using cysteine as a chiral inducer. The nanozymes exhibited remarkable enantioselective catalytic activity to 3,4-dihydroxy-phenylalanine (DOPA) enantiomer. Notably, L -Cys@Au/Fe Hops, comprising right-handed helical nanopetals, exhibited elevated catalytic efficiency for L -DOPA over D -DOPA, whereas the reverse held for D -Cys@Au/Fe Hops. The molecular dynamics simulations demonstrated hydrogen bonding interactions between the active site and substrate, thereby revealing how steric effects affected the enantioselective catalysis of chiral DOPA by L/D -Cys@Au/Fe Hops. Moreover, the chiral nanozymes were developed into a test paper sensor due to their exceptional stability, which can achieve the visual detection of DOPA enantiomer combined with a smartphone platform. This work is significant in advancing the design and practical utility of highly selective enzyme mimics. [ABSTRACT FROM AUTHOR]

To further enhance the performance of nano-silica modified M-phenylene isophthalamide (MPIA) insulation paper, nano-SiO2 particles are modified by 3-aminopropyltriethyloxy silane (APTS) surface into meta-aramid insulation paper to form grafting nano-silica particles (GNP). In order to find the relative best performance of the nanoparticle doping ratio, molecular dynamics simulations were used to study the effect of different GNP volume fractions on the mechanical parameters of the MPIA amorphous region, and the highest mechanical performance was obtained with a volume fraction of 9.4 vol. %. Under this doping condition, the interaction between GNP and MPIA fibers was enhanced by the formation of a large number of hydrogen bonds. The addition of GNP decreased the diffusion of water, acid and gas in MPIA fibers and the influence of these substances on the thermal stability of aramid fibers. All these indicate that the addition of GNP further improves the performance of aramid insulation paper, improves the thermal stability of aramid insulation paper and delays the aging process of oil-immersed aramid insulation paper. This article provides a reference and basis for the preparation of meta-aramid insulation paper with relatively good thermal stability. [ABSTRACT FROM AUTHOR]

The performance of insulating paper cellulose is an important factor affecting the normal operation of electric power equipment. This paper uses molecular dynamics methods to establish pure cellulose, hBN‐modified cellulose, 3‐aminopropyltriethoxysilane (KH550), 3‐glyoxypropyltrimethoxysilane (KH560), and 3‐methylpropoxypropyltris (KH570) grafted with hBN modified cellulose models. The effect of cohesive energy density (CED), thermal conductivity (TC), mean square displacement (MSD), free volume, glass transition temperature (Tg), and mechanical properties on the thermomechanical properties of cellulose are investigated and compared. The results indicate that all three silane coupling agents can enhance TC, thermal stability, and mechanical properties of the cellulose models. Among them, KH550 is the best grafting method for hBN/cellulose system as KH550 graft not only significantly enhances TC by 114.29% and Tg by 23.88% but also significantly strengthens the toughness and resistance to deformation of cellulose by over 50%. [ABSTRACT FROM AUTHOR]

The ecological environment is increasingly damaged due to the impact of mineral oil extraction and leakage. As a kind of sustainable resource, a vegetable oil transformer has bright application prospects in future. However, the stability of vegetable oil has always been a problem to be solved. In addition, the metallic copper inside the transformer has a certain catalytic effect on the deterioration of vegetable oil. In this article, a copper–oil–paper insulation model is established. Based on the molecular dynamics simulation method, the catalytic mechanism of copper on the deterioration of oil-paper insulation is revealed from the microscopic level. Then, the effects of temperature, contact area, and oxygen on the catalytic effect of copper are discussed. The results show that copper could accelerate the decomposition of oil-paper insulation by attracting H atoms and O atoms in oil-paper. The increase in temperature accelerates the progress of the catalytic reaction and aggravates the deterioration of oil-paper insulation. The oxygen concentration has an important influence on the catalytic reaction of copper. As the oxygen concentration increases, the catalytic effect of copper is weakened. The abovementioned research could provide some theoretical reference for further exploration of effective oil-paper insulation deterioration protection technology. [ABSTRACT FROM AUTHOR]

Polyhedral oligomeric silsesquioxane (POSS) has a total of eight substituents. The number of substituents determines the modification effect of POSS. Through simulation of molecular dynamics, this paper explores how the number of substituents affects the POSSmodified cellulose insulation paper. Specifically, the mechanical properties, thermal stability and polarizability were calculated for cellulose models with 1-phenyl POSS, 2-phenyl POSS, 3-phenyl POSS, 4-phenyl POSS, 5-phenyl POSS, 6-phenyl POSS, 7-phenyl POSS, and 8-phenyl POSS, respectively. The results show that the cellulose model modified by 6-phenyl POSS achieved better effect than the other seven models, as evidenced by its distinctively large bulk modulus, shear modulus, and elastic modulus. Besides, the cellulose model modified by 6-phenyl POSS had the most stable and the minimum mean square displacement (MSD). This is because the mechanical properties of the insulation paper are improved, as the motion of cellulose chains is inhibited by the nano-size effect of POSS and the effect of phenyls. Further, the cellulose model modified by 6-phenyl POSS also had the smallest polarizability among the modified models. Therefore, the 6-phenyl POSS-modified cellulose model can effectively reduce the polarizability of cellulose, uniform the electric field distribution in oil-paper insulation system, and thus enhance the insulation property of transformers. [ABSTRACT FROM AUTHOR]

The recovery of valuable minerals in froth flotation industry relies on finding inexpensive and environmentally friendly reagents that selectively adsorb upon surfaces and interfaces. Computer simulations, especially when extended, provide access to detailed mechanistic information on solvent configurations and may ascertain crucial dynamical events over the adsorption process. Further, in silico throughput screening can prevent both the high cost of experiments and the related risks to the environment. Yet, a better compromise between accuracy and computational cost must be met. Machine learning (ML) simulations may ease the latter and suggest solidophilic reagents able to improve the flotation efficiency, shedding new light on discerning descriptors able to accurately capture the nature of the molecule-surface interaction. In this work, our recent advancements in modeling of new accurate mineral-water interfaces based on active learning of ab initio molecular dynamics trajectories have been introduced. The case of some habitual oxides and minerals liberated in mining industry will be taken as examples. • How the mineral slab may influence the layering of surfactant water molecules. • Water kinetics at the hematite, ferrosilite and magnetite interfaces. • Competing adsorption phenomena between oleic acid and amylopectin on calcite surface. • In silico screening of flotation reagents employing machine learning methodologies. [ABSTRACT FROM AUTHOR]

Cold atmospheric-pressure plasma is used widely for treating material surfaces and can be considered for modifying insulation paper (IP) to improve its surface performance. However, the mechanism for interaction between reactive oxygen species (ROS), which are the dominant components of such plasma, and IP is important for setting experimental parameter values but is difficult to observe experimentally. In this paper, reactive force field molecular simulation technology is used to study the mechanism for interaction between ROS (O atoms, OH radicals, and H2O2 molecules) and cellulose, which is the main component of IP. The results show that the ROS can abstract H atoms, and the H2O2 molecules can also abstract hydroxyl groups from a cellulose chain, resulting in changes to the cellulose chain structure, such as reductions of the hydroxyl groups and pyran rings and formations of aldehyde and vinyl groups. The three types of ROS exhibit different reactivities when reacting with the cellulose chain, and the difficulty of breaking different bonds therein also differs, which influences how the chemical groups change the cellulose chain. This study provides basic insight into the mechanism for interaction between ROS and IP at the atomic level as well as offering some guidance for practical experiments. [ABSTRACT FROM AUTHOR]

• Nacre-like FG/Al energetic paper was designed and prepared. • A significantly enhanced energy and pressure output are obtained. • FG/Al energetic papers shown self-propagate combustion reaction at micro-scale. • The chemical reaction mechanism was distinctly elucidated. • FG/Al energetic paper displayed high flexibility and strain. Developing functional devices requires energetic materials with comprehensive performance including high energy density, excellent chemical reactivity and mechanical properties. Herein, an effective strategy inspired by nacre-like architecture was employed to construct new fluorographene (FG)/nano-aluminum (Al) energetic paper through a vacuum filtration induced self-assembly process. FG/Al energetic paper showed ultrahigh reactivity and high flexibility owing to combined effect of the nacre-like architecture and interfacial interaction. FG/Al energetic paper exhibited significantly enhanced energy output (3257.7 J/g) and self-propagate combustion reaction with high pressure output at micro-scale. Chemical reaction mechanism was distinctly elucidated based on reactive molecular dynamics simulations and the combustion products of FG/Al energetic paper. More interestingly, FG/Al energetic paper displayed high flexibility and strain (5.39%) reported for the first time. The bio-inspired route provides a promising approach to design advanced energetic materials for applications in transportation, aerospace, and military industries. [ABSTRACT FROM AUTHOR]

Organic acid is an important factor that accelerates the aging of cellulosic insulation materials. In this study, the interactions between cellulose and five acids, representative of what may be found in an aging transformer, were studied using molecular dynamics. The adsorption process of the five acids onto the surface of crystalline cellulose shows that the three low molecular acids are more readily adsorbed onto cellulose than the two high molecular acids. The deformation and adsorption energies of the acids all increase with an increase in molecular weight when they are stably interacting with cellulose. However, the differences between adsorption energies and deformation energies are positive for the three low molecular acids, whereas they are negative for the two high molecular acids. This indicates that the attachments onto cellulose of low molecular acids are considerably more stabilized than those of the high molecular acids. This is consistent with the experimental results. Furthermore, based on the calculated solubility parameters of acids, the experimental result that the three low molecular acids are to a large degree absorbed onto the cellulose, whereas the two high molecular acids remain in the oil, was theoretically elucidated using the theory of similarity and intermiscibility.

Nowadays, the goal of carbon peaking and carbon neutrality has become a global consensus, and electrochemical CO2 reduction to provide high-value power fuel is one of the major technical approaches attracting significant research interests and application prospects. However, the inevitable hydrogen evolution reaction in water-based electrolyte systems crowds out the reactive sites of active metals, causing a low CO2 conversion efficiency. In this work, Zn nanosheets were prepared via electrodeposition on the surface of carbon paper and then modified with polytetrafluoroethylene (PTFE) to tune the wetting angle of the electrolyte. A CO faradaic efficiency of 90.2% was achieved for Zn NS-8% PTFE (contact angle: 136.8°) at the electrolytic voltage of −1.0 V vs. RHE along with an overall current density of −7.9 mA cm−2. Experimental results and molecular dynamics simulation revealed that PTFE weakened the aggregation of H2O molecules and was more beneficial for capturing and adsorbing CO2 molecules near the electrode surface. The active sites of hydrogen production were transformed into the reaction center for electrocatalytic CO2 reduction due to the hydrophobicity of the electrode, and the accumulation of the local CO2 concentration accelerated the kinetic activity for electrochemical conversion (CO2 to CO). This strategy of tuning the local environment offers an alternative approach for effective electrode manufacturing in liquid electrolytes. [ABSTRACT FROM AUTHOR]

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cellulose insulating paper is widely used in the power industry for its good electrical insulating properties. Moisture sharply increases its conductivity, which directly leads to the weakening of insulation performance and greatly increases the risk of subsequent electric field distortion and insulation breakdown. This paper focuses on the microscopic mechanism of moisture changing the characteristics of charge transport in cellulose insulation and attempts to reveal the related conductivity mechanism. To achieve this purpose, microscopic and macroscopic perspectives are integrated and several simulation and experimental methods are utilized comprehensively. The molecular dynamics simulation results showed that most water molecules in damped cellulose were individually and uniformly adsorbed on the hydroxyl groups by hydrogen bond, and the quantum chemistry computation results showed that the lowest unoccupied molecular orbital more appeared on the water molecule and the corresponding density of state increased. Then, experimentally, it was confirmed that the trap energy level decreased by the thermally stimulated current method. On this basis, the promotion effect of moisture on charge transport is predicted and verified by polarization and depolarization current methods. As the moisture content increased, more charge carriers escaped from the trap by hopping and participated in long-range continuous charge motion. Therefore, after dampness, the current of cellulose insulating paper increased exponentially with the increase in electric field strength, which was consistent with the hopping conductivity mechanism. [ABSTRACT FROM AUTHOR]

Thermodynamic properties of cellulose insulation paper are vital factors affecting the life of a transformer; in order to obtain cellulose insulation paper with better thermodynamic properties, three types of silane coupling agents—3-aminopropyltriethoxy silane (KH550), 3-glycidoxypropyltrimethoxy silane (KH560), and 3-methacryloyloxypropyltrimethoxy silane (KH570)—were grafted on the surface of nano-SiO2, and thermodynamic properties of cellulose modified with nano-SiO2 were explored. The molecular dynamics method was used to establish a composite model of nano-SiO2/cellulose. Also, different silane coupling agent grafted nano-SiO2/cellulose models were established to explore the effect of mechanical properties, interaction energy, free volume, and hydrogen bonds on thermodynamic properties. The results showed that KH550 was the best modification of the nano-SiO2/cellulose system among the three grafted silane coupling agents because KH550 grafted on the surface of nano-SiO2 formed more hydrogen bonds in the cellulose system. The interfacial bonding strength between the nano-SiO2 and the cellulose chains can effectively improve the thermal stability of the cellulose insulating paper. [ABSTRACT FROM AUTHOR]

With the improvement of operation requirements of power equipment, the stable operation of insulation of equipment is very important. Among them, insulating paper is one of the main factors affecting the state of equipment. Therefore, it is important to improve the performance of insulating paper. The pure cellulose model and h‐BN/cellulose composite model are established to analyze the improvement of thermal and mechanical properties of insulating paper cellulose. The effects of different contents of h‐BN doping on the properties of cellulose are studied by comparing the mechanical parameters, cohesive energy density, thermal conductivity, mean square displacement, and free volume of cellulose before and after h‐BN doping through molecular dynamics method. The results indicate that the thermal conductivity and thermal stability of cellulose are improved by more than 15% at the h‐BN mass fraction of 2% and 3%, the shear modulus and elastic modulus are enhanced by more than 50%, and the deformation resistance and ductility of the composites are enhanced when the mass fraction of h‐BN is 2%. The doping of h‐BN has an important impact on improving the thermodynamic properties of cellulose, which is of great significance to improving the insulation performance of power equipment and reducing equipment faults. [ABSTRACT FROM AUTHOR]

Molecular simulation technology is a new technology emerging with the rapid development of computer technology. It has the advantages of clear microscopic models, in-depth and precise calculation etc., it has been widely used in the oil–paper insulation system of transformer in recent years. Based on the application of molecular simulation technology in the oil–paper insulation system of transformers in this study, the current research status and progress of molecular simulation in these area are elaborated in detail from the aspects of transformer insulating oil and insulating paper according to the domestic and foreign literature, and the application of molecular simulation technology in plant insulating oil and nano-modified insulating oil is emphatically analysed. The complementing research method of molecular simulation and experiment is pointed out, which provides certain reference for solving many problems existing in the field of oil–paper insulation system of transformers. [ABSTRACT FROM AUTHOR]

Moisture is an important factor affecting the insulation properties of transformers. Due to the limitations of macroscopic experimental methods, the diffusion of water at oil-paper interface cannot be accurately measured. Therefore, molecular dynamics method was used in this work to establish oil-paper layer model of 105 atoms. Through jointly analysing the aggregation degree, diffusion coefficient, free volume as well as radial distribution function of water molecules, the diffusion mechanism of water molecules at oil-paper interface was studied. The results show that when the initial water content in paper was high, water molecules would accumulate at oil-paper interface to form the local high-water region during heating. The polarisation of the electric field strengthened the hydrogen bonding interaction between water molecules and increased the probability of occurrence of the high-water region. Meanwhile, electric field reduced the free volume and diffusion coefficient of water molecules and rendered its diffusion coefficient anisotropic. What’s more, when the electric field was combined with the temperature field, the electric field played a leading role in the diffusion of water molecules while the temperature field was less affected. Diffusion coefficients of water molecules at different temperatures from molecular dynamics simulations were well consistent with experimental results, which verified the rationality of the model. [ABSTRACT FROM AUTHOR]

We introduce a family of rock-paper-scissors-type models with ZN symmetry (N is the number of species), and we show that it has a very rich structure with many completely different phases. We study realizations that lead to the formation of domains, where individuals of one or more species coexist, separated by interfaces whose (average) dynamics is curvature driven. This type of behavior, which might be relevant for the development of biological complexity, leads to an interface network evolution and pattern formation similar to the ones of several other nonlinear systems in condensed matter and cosmology. [ABSTRACT FROM AUTHOR]

[Display omitted] • The simulation results successfully guided the preparation of the insulating paper. • Nano-SiO 2 enhances the interfacial binding and compatibility of composite fiber. • Nano-SiO 2 improved the mechanical and insulating properties of the insulating paper. • Nano-SiO 2 reduced the energy barrier of composite fiber and reduce polarization loss. Following the surge in power loads and continuous improvement in the voltage level, insulating papers' mechanical and electrical properties face new challenges. However, traditional inefficient "tentative" trial and error experiments are formidable to rapidly and efficiently prepare cellulose composite insulating paper because the direct scientific theory or simulation guidance is insufficient. To solve this problem, the nano-silica(nano-SiO 2)/polyimide(PI)/cellulose composite models were designed and their mechanical, and dielectric properties were predicted by molecular dynamics (MD) simulation. The preparation of corresponding nano-SiO 2 /PI/cellulose insulating paper was guided by the MD simulation results and their surface morphology, mechanical properties, and electrical properties were investigated. The experimental results are in good agreement with the MD simulation results and confirmed that P3 insulating paper possesses the best comprehensive performance, and its tensile strength, relative permittivity, dielectric loss, volume resistivity, and breakdown strength are 71.44 MPa, 2.39, 0.2%, 5.16 × 1015 Ω∙m, and 75.8 kV∙mm−1, respectively. This work proves the feasibility and effectiveness of using MD simulation to guide the development of new insulating papers, and compared with the existing traditional preparation methods, this method is expected to be applied to study various new materials in the future and promote the vigorous development of new materials. [ABSTRACT FROM AUTHOR]

Polyhedral oligomeric silsesquioxane (POSS) has eight substituent groups, which can be substituted with various substances to obtain different modification effects. In order to study the effect of different substituents on the modification of cellulose by POSS and its internal mechanism, the pure cellulose model and the modified cellulose with three kinds of POSS derivatives, polyoctamethyl silsesquioxane (PMSQ), polyoctaphenyl silsesquioxane (PPSQ) and polyoctaaminophenyl silsesquioxane (OAPS), were established by molecular dynamics method. The thermal stability parameters and polarizability were calculated. The simulation results showed that different POSS derivatives can improve the thermal stability of insulating paper cellulose, and the modified effect of OAPS is the best. Compared with the unmodified model, the glass transition temperatures of the modified cellulose models of PMSQ, PPSQ and OAPS increased by 58 K, 63 K and 71 K, respectively. The mean square displacement of the modified models is significantly reduced, and the free volume is increased. The addition of POSS derivatives increase the entanglement between the cellulose chains, and compresses the gap between the cellulose molecular chains to suppress the movement of the cellulose chain. It is also found that the addition of POSS derivatives can effectively reduce the polarizability of cellulose, even the electric field distribution in oil paper insulation system, so as to enhance the insulation of transformer. [ABSTRACT FROM AUTHOR]

In this paper, polysiloxane is used to modify insulation paper cellulose, and molecular dynamics methods are used to evaluate the glass transition temperature and mechanical properties of the paper before and after the modification. Analysis of the static mechanical performance of the model shows that, with increasing temperature, the elastic modulus of both the modified and unmodified cellulose models decreases gradually. However, the elastic modulus of the modified model is greater than that of the unmodified model. Using the specific volume method and calculation of the mean square displacement of the models, the glass transition temperature of the modified cellulose model is found to be 48 K higher than that of the unmodified model. Finally, the changes in the mechanical properties and glass transition temperature of the model are analyzed by energy and free volume theory. The glass transition temperatures of the unmodified and modified cellulose models are approximately 400 K and 450 K, respectively. These results are consistent with the conclusions obtained from the specific volume method and the calculation of the mean square displacement. It can be concluded that the modification of insulation paper cellulose with polysiloxane will effectively improve its thermal stability. [ABSTRACT FROM AUTHOR]

Cellulose, hemicellulose, and lignin are the major chemical components in wood paper. Various types of wet and dry strength additives are used to enhance the optical and mechanical properties of recycled paper. One of the possible materials is the carbon nanotube. In order to explore the probability of the use of carbon nanotubes as reinforcing materials and to understand how carbon nanotubes affect the mechanical properties of paper, a single-walled carbon nanotube is inserted into a I β cellulose nanocrystal, and its mechanical properties are studied by using energy minimization and molecular dynamics (MD) simulations. During simulations, the crystals are stretched in the axial direction at a constant speed, and stress and strain are computed and recorded at the atomic level. Our results indicate that carbon nanotube can significantly enhance the mechanical properties of paper. [ABSTRACT FROM AUTHOR]

To study the microscopic thermal aging mechanism of insulating paper cellulose through molecular dynamics simulation, it is important to select suitable DP (Degree of Polymerization) and force field for the cellulose model to shorten the simulation time and obtain correct and objective simulation results. Here, the variation of the mechanical properties and solubility parameters of models with different polymerization degrees and force fields were analyzed. Numerous cellulose models with different polymerization degrees were constructed to determine the relative optimal force field from the perspectives of the similarity of the density of cellulose models in equilibrium to the actual cellulose density, and the volatility and repeatability of the mechanical properties of the models through the selection of a stable polymerization degree using the two force fields. The results showed that when the polymerization degree was more than or equal to 10, the mechanical properties and solubility of cellulose models with the COMPASS (Condensed-phase Optimized Molecular Potential for Atomistic Simulation Studies) and PCFF (Polymer Consistent Force Field) force fields were in steady states. The steady-state density of the cellulose model using the COMPASS force field was closer to the actual density of cellulose. Thus, the COMPASS force field is favorable for molecular dynamics simulation of amorphous cellulose. [ABSTRACT FROM AUTHOR]

We report a novel OLED material discovery process and several applications based on AI technology. This process in which six AI modules that generate molecular structures with active learning algorithm, predict multiple properties, analyze novelty, predict synthetic scheme, predict relative synthesizability and predict device characteristics are linked one after another. Also, we introduce some cases in which materials designed by this process were actually synthesized and applied to devices for evaluation to confirm the improvement of characteristics. [ABSTRACT FROM AUTHOR]

In view of the small molecular model established in the field of high voltage insulation, the actual operation of transformer cannot be fully reflected at micro-level. Therefore, this paper aims to improve the performance of computing environment and expand molecular scale. Firstly, two servers were connected through a high-speed communication network as the initial cluster architecture. Secondly, spatial decomposition and load balancing algorithms were used to improve the operation efficiency of cluster. Meanwhile, the oil-paper composite media model of 105 atoms could be established based on this cluster, but it consumed a lot of time. Therefore, we analysed the relationship between operation efficiency and four characteristic quantities such as central processing unit performance, number of cores, simulation time and number of nodes. Then the highest point of cluster operating efficiency was found through continuous optimisation. It can be summarised that the calculating speed of cluster is nearly 10 times faster than that of the large server. Meanwhile, according to the results based on this cluster, it can be concluded that water molecules would migrate towards the oil during heating. When the initial moisture content in paper is high, the high water region would appear at the oil-paper interface. [ABSTRACT FROM AUTHOR]

Xylanases are used in several industrial applications, such as feed additives, the bleaching of pulp and paper, and the production of bread, food, and drinks. Xylanases are required to remain active after heat treatment at 80–90 °C for 30 s to several minutes due to the conditions of feed pelleting. Also, xylanases need to be active at 60–70 °C for several hours while bleaching of pulp and paper or manufacturing of bread, food, and drinks is performed. Xylanases of the glycoside hydrolase family GH10 are good candidates for application in such processes because of their high thermostability and, in particular, as feed additives because of their insensitivity to protein inhibitors in cereal feeds. In the study, the thermostability of GH10 xylanase E from Penicillium canescens was improved to reach a half-inactivation period of 2 min at 80 °C compared to 21 s for the wild-type enzyme (WT). Enzymatic activity was increased by 22–48 % at 40–70 °C, which improved the action of the enzyme as a feed additive in the gastric system of animals and during bleaching of pulp and paper. Molecular dynamics simulations demonstrated lower flexibility of the tertiary structure of the engineered enzyme at elevated temperatures compared to WT. The residues W113, Q116, W313, and W321 in the (−1) and (−2) subsites for the substrate binding were less flexible. In the simulations, the engineered enzyme had a comparable content of α-helixes, 3 10 -helixes, β-sheets, and β-bridges as WT, but a lower content of coils and a higher content of β-turns. [Display omitted] • Thermostability was improved by six times to reach t 1/2 of 2 min at 80 °C. • Enzymatic activity was increased by 22–48 % at 40–70 °C. • Stability of active center cleft and surface loops and α-helixes was increased. [ABSTRACT FROM AUTHOR]

This paper is a discussion of a recent publication by Sekkal and coworkers, which investigated the elasticity, cohesion, and stability of the C-S-H (001) surface as a function of porosity using molecular dynamics simulations. In our discussion, we highlight some doubts about their model system for the C-S-H structure. We also comment on the defined stoichiometry, applied methodology and on various incongruous results and erroneous interpretations. We also draw attention to the lack of fundamental details provided by the authors and how it could be improved both conceptually and practically to allow readers to better understand the paper. [ABSTRACT FROM AUTHOR]

Cellulose is the main component of transformer insulating paper. In this paper, the pyrolysis mechanism of cellulose is studied by means of computational chemistry. This study is aimed at exploring the generation process of the methanol from cellulosic insulating paper at the atomic level. A simulation scheme of cellulose pyrolysis with detailed reaction pathways for methanol production has been obtained that is not readily accessible by experiments. The molecular dynamics method based on reactive force field (ReaxFF) is adopted to simulate the pyrolysis of cellobiose. A model composed of 40 cellobioses simulated at 500–3000 K was established, and the force biased monte-carlo is mixed into ReaxFF to make it closer to the actual situation and ensure the reliability. The result reveals that the –CH2– group from the C5 (or C 5 ′ ) group in cellobioses grabbed the nearby H atom to form methanol. In the pyrolysis process of cellobioses, methanol is stable at the early stage but unstable even disappeared in the later stage. The pre-exponential factor A and activation energy Ea of the ReaxFF-MD simulation are consistent with previous experimental results. Thus, this study provides an effective theory of the methanol as an indicator to evaluate the aging condition of cellulosic insulating paper in the early stage at the atomic level. [ABSTRACT FROM AUTHOR]

Cellulose insulation paper is an essential part of the transformer oil-paper insulation system, and many types of nano-modified insulating paper are available. For studying the effects of various nano-modified molecules on cellulose and the differences in performance, the pure cellulose model and polyoctaaminophenylsesquioxane and grafted 3-aminopropyltriethoxysilane (KH550) SiO2 and Al2O3 cellulose models were developed using molecular dynamics methods, and the mechanical properties and thermally stability were calculated and compared. The findings show that, in general, all three nano-modification models improved the thermal stability and mechanical properties, with nano-SiO2-KH550 cellulose having the best overall modification effect. In terms of mechanical properties, the nano-SiO2-KH550 cellulose showed the largest increase in compressive strength, with an 18.1% improvement. In terms of thermal stability, the KH550 grafted nano-silica/cellulose composite model showed the best modification effect, as evidenced by the smaller cohesive energy density and free volume region compressing the space between cellulose molecules, making the modified cellulose more compact internally, thus achieving the effect of inhibiting the movement of cellulose chains. [ABSTRACT FROM AUTHOR]