A method for analyzing the influence of the microstructure of ethylene-propylene-diene rubber on surface discharge

Abstract

A method for analyzing the influence of the microcosmic characteristics of ethylene-propylene-diene rubber molecules on surface discharge, comprising the following steps: step one, constructing an ideal molecular chain model according to the actual production ratio of ethylene-propylene-diene rubber; step two, performing structure optimization and frequency calculation on the initial ethylene-propylene-diene rubber molecules by using the density functional theory, and obtaining an optimized model of ethylene-propylene-diene rubber molecules with relatively accurate and lowest energy; and step three, analyzing the influence of the microcosmic characteristics of ethylene-propylene-diene rubber under electric field on surface discharge through the ground state microcosmic properties of molecular geometric structure, infrared spectrum, dipole moment, orbital energy level, space charge trap depth, state density and molecular surface electrostatic potential. The method provided by the application can solve the technical problem of discussing the influence of microcosmic structure and space charge distribution on discharge from the molecular atomic level.

Description

Technical Field

[0001] This invention relates to the field of cable insulation technology, and in particular to a method for analyzing the influence of the microscopic properties of EPDM rubber molecules on surface discharge. Background Technology

[0002] Ethylene-propylene-diene monomer (EPDM) rubber possesses excellent flexibility, corrosion resistance, and dielectric properties, making it widely used in medium- and high-voltage cable insulation in applications such as coal mines, oil extraction, and rail transportation. However, its actual operating conditions are complex, and surface discharge due to uneven electric field distribution often occurs at cable terminals or joints, leading to a deterioration in insulation material performance and compromising equipment operational safety. Therefore, researching the surface discharge mechanism of EPDM rubber insulation materials is of great significance for improving operational reliability and enhancing insulation material performance.

[0003] Since ethylene propylene rubber (EPR) was adopted as a cable insulation material, most research has focused on its thermo-oxidative aging, electrical dendrite formation, surface tracking, and interfacial charge, all of which are closely related to the space charge distribution. The space charge distribution not only affects the electric field distribution but also relates to the electrical aging and dielectric properties of the polymer material. For EPR, traps of varying depths can form within the material due to manufacturing processes and human-caused damage. The effective electrons required for the initial stage of surface discharge are closely related to the presence of these traps.

[0004] Currently, most research on surface discharge is based on experiments. Macroscopic experiments cannot observe the impact of changes in the internal structure of materials on charge transport, nor can they understand the influence of atomic-level electronic excitation processes on discharge. With the rapid development of computational high-voltage engineering, molecular simulation technology is widely used in medium- and high-voltage insulation fields. Therefore, this invention uses molecular simulation to combine material properties with the surface discharge phenomenon. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for analyzing the influence of the microscopic properties of EPDM rubber molecules on surface discharge, thereby solving the technical problem of exploring the influence of microstructure and space charge distribution on discharge at the molecular and atomic level.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for analyzing the influence of the microscopic properties of ethylene propylene diene monomer (EPDM) rubber molecules on surface discharge, comprising the following steps:

[0007] Step 1: Construct an ideal molecular chain model based on the actual production ratio of EPDM rubber;

[0008] Step 2: The initial EPDM rubber molecule was optimized and its frequency was calculated using density functional theory, resulting in a more accurate and lowest-energy optimized model of the EPDM rubber molecule.

[0009] Step 3: The influence of the microstructure of EPDM rubber on surface discharge under an electric field is analyzed by examining the ground-state microstructure of molecular geometry, infrared spectroscopy, dipole moment, orbital energy level, space charge trap depth, density of states, and ground-state electrostatic potential of the molecular surface.

[0010] Step four: Using time-dependent density functional theory, the excitation energy, ultraviolet-visible absorption spectrum, charge transfer spectrum, and excited-state microscopic properties of EPDM rubber molecules are calculated to analyze the influence of the microscopic properties of EPDM rubber on surface discharge under an electric field.

[0011] Preferably, the actual production ratio of the EPDM rubber is ethylene, propylene and a third monomer polymerized in a ratio of 5:4:1.

[0012] Preferably, the space charge trap depth is expressed as the electron affinity of the molecular system before defects are generated minus the electron affinity after defects are generated; the electron affinity EEA is the energy difference generated when the optimized neutral molecule gains electrons and becomes an anion, as shown in equation (1):

[0013] E EA =27.211×[E(N)-E(N+1)] (1)

[0014] Where E(N) and E(N+1) are the energies of the neutral molecule and the anion molecule, respectively.

[0015] Preferably, the surface electrostatic potential of a molecule reflects the movement of charge and provides information on the reactivity of the molecule. The distribution of charge at any location will generate a molecular electrostatic potential (ESP), as shown in equation (2):

[0016]

[0017] Where V(r) represents the electrostatic potential at position r, which is determined by the atomic nucleus V nuc (r) and electron V ele (r) Joint contribution, Z A R is the nuclear charge of atom A. A Let r be the nuclear coordinate of atom A, and ρ(r') be the electron density.

[0018] Preferably, the excitation of charges under the influence of an electric field can evolve continuously. While DFT is based on the ground-state charge density, time-dependent density functional theory (TDDFT) is an effective method for studying the excited-state properties of materials and describing their response under external fields. Using TDDFT, the excited states of EPDM rubber molecules are calculated on the same functional and basis set as the ground state. The expression for the hole-electron charge density is defined as follows:

[0019]

[0020]

[0021] In the formula, is the r-coordinate vector; ρ hole (r) and ρ ele (r) represents the hole density distribution and the electron density distribution, respectively. Both are divided into two parts: the local term loc and the cross term cross.

[0022] Preferably, the charge transfer spectrum is based on the idea of ​​charge transfer between fragments. Assuming the molecule is divided into several fragments, the total UV-Vis absorption spectrum is decomposed into different sub-curves from the perspective of charge transfer between fragments. This allows for a direct and clear view of charge transfer between fragments. Therefore, the absorption curve of electron transfer from fragment A to fragment B can be expressed as equation (5):

[0023]

[0024] Where E (λ) The energy corresponding to the absorption wavelength λ is represented by i, which is the summation over all excited states, and f is the oscillator strength. It is the number of electrons transferred from A to B, E i exc G is the excitation energy, and G is the broadening function.

[0025] Preferably, the structural optimization and frequency calculation employ the M06-2X functional and 6-31g(d) basis set from density functional theory (DFT). All models are built and optimized using Gaussian 09 software, and the output results are analyzed using Multiwfn 3.8 software.

[0026] This invention provides a method for analyzing the influence of the microscopic properties of EPDM (ethylene propylene diene monomer) rubber molecules on surface discharge. A molecular chain model of EPDM rubber was constructed, and density functional theory was used to analyze the changes in the microscopic properties of EPDM rubber under an external electric field. The influence on surface discharge was explored from a molecular and atomic perspective. This method is helpful in analyzing charge transfer within EPDM molecules, providing a microscopic basis for understanding surface discharge phenomena, and is also of great significance for analyzing the lifetime of insulating materials. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0028] Figure 1 This is the optimized EPDM molecular diagram of the present invention;

[0029] Figure 2 The following are infrared spectra of EPDM molecules under different electric fields according to the present invention;

[0030] Figure 3 This is a graph showing the variation of the dipole moment of the EPDM in this invention with the electric field intensity;

[0031] Figure 4 This is a schematic diagram of the frontier orbitals and energy level distribution of the EPDM molecules of this invention;

[0032] Figure 5 This is an optimized molecular model of EPDM in the oxidation process of this invention;

[0033] Figure 6 This is a molecular density of states diagram of EPDM under different power plants according to the present invention;

[0034] Figure 7(a) is a three-dimensional cloud diagram of the molecular surface electrostatic potential when F = 0.000au according to the present invention;

[0035] Figure 7(b) is a three-dimensional cloud diagram of the molecular surface electrostatic potential when F = 0.008au according to the present invention;

[0036] Figure 8 The ultraviolet-visible absorption spectra of EPDM molecules under different electric fields are shown in this invention.

[0037] Figure 9(a) shows the charge transfer spectrum of the EPDM when F = 0.000au according to the present invention;

[0038] Figure 9(b) shows the charge transfer spectrum of the EPDM when F = 0.008au according to the present invention;

[0039] Figure 10 This is a diagram showing the hole-electron orbital transitions in the absence and presence of an electric field, according to the present invention. Detailed Implementation

[0040] An ENB-type EPDM molecular chain was constructed using the quantum chemistry software Gaussian 09. Since traps may be distributed at different positions or on different molecular chains, they will not affect each other before insulation failure occurs, meaning there is no conductive path coupling. Furthermore, calculating hundreds of thousands of molecules using simulation software is impractical. Considering the relationship between the degree of polymerization and machine time, and based on bond length and bond angle comparisons, the degree of polymerization of the molecule is considered to have no significant impact on the research content. Therefore, the trap distribution in the EPDM molecule was approximated, and single-chain segments were selected for study. Based on the actual production ratio of EPDM, ethylene, propylene, and the third monomer were polymerized in a 5:4:1 ratio in the constructed molecular chain. Moreover, the ends of the EPDM molecular backbone are prone to breakage under an external electric field, forming unsaturated dangling bonds. Therefore, to saturate the structure and reduce the influence of breakage points on the model, hydrogen atoms were used to fill the breakage sites of the backbone under approximate hydrogen bonding. Thus, an ideal EPDM molecular chain model was constructed.

[0041] Next, density functional theory (DFT) was used to optimize the structure and calculate the frequencies of the initial EPDM rubber molecule on the M06-2X functional and the 6-31g(d) basis set. During the calculation, the keywords nosymm and int = ultrafine were added to eliminate the system coordinate orientation problem after applying an external electric field and to improve the integration accuracy. Finally, the results were obtained... Figure 1 The most accurate and lowest-energy EPDM molecular optimization model is used. An electric field of F = 0 to 0.008au (1a.u. = 5.142 × 10¹¹ V / m) is then applied along the negative x-axis to analyze the structure, frontier orbital energy levels, trap depth, density of states, electrostatic potential, and other ground-state properties of EPDM molecules, as well as the microscopic properties of excited states.

[0042] The specific steps are as follows:

[0043] Step 1: Analysis of changes in molecular geometry. In Table 1, A(1,2,8), A(32,33,37), and A(48,68,69) represent the CCC-bond angles at the beginning, middle, and end of the molecular backbone, respectively. With increasing external electric field, A(1,2,8), A(32,33,37), and A(48,68,69) gradually increase, indicating that under the influence of the electric field, the EPDM molecular chain gradually extends and straightens. This weakens the resistance to electron migration, making charge migration within the polymer easier and affecting the properties of the insulating material.

[0044] Table 1. Partial structural parameters of EPDM molecules under different electric fields.

[0045]

[0046] Based on the correction factor of 0.947 provided by the CCCBDB database, the frequencies calculated under no electric field and electric field of 0.008au were corrected using Multiwfn 3.8 software to obtain EPDM infrared spectra as a function of electric field, as shown below. Figure 2 1452cm -1 The bending vibration peak of the methyl group at 1363 cm⁻¹ -1 The ratio of the bending vibration peaks of the methylene group (—CH2—) increases with the increase of the electric field, indicating that under the action of the electric field, the main chain and side chain in the EPDM molecular structure tend to undergo chain breakage, resulting in changes in the molecular geometry.

[0047] Molecular polarity can be represented by the dipole moment. The calculation results are as follows: Figure 3 As shown, the dipole moment of EPDM molecules gradually increases from 0.748 Debye (1 Debye ≈ 3.335 × 10⁻³⁰ C·m) to 8.164 Debye under the influence of an electric field, and the graph approximates a straight line. The increase in dipole moment causes a relative displacement of the centers of gravity of positive and negative charges, resulting in a greater and greater distance between them. The induced dipole moment is in the same direction as the electric field, altering the original electric field distribution of the molecule. The interaction between the internal and external electric fields affects the charge distribution, increasing the molecular polarity and making it easier to form polarized charges on the material surface, causing polarization of the dielectric. Furthermore, since the internal attraction of electrons to the molecule is limited, when the applied electric field continues to increase, the molecular dipole moment will exceed its upper limit, causing electrons to escape the attraction of the atomic nucleus and become free electrons. These free electrons move directionally under the influence of the electric field, which to some extent reduces the insulation properties of the material.

[0048] Step 2: Analysis of the frontier orbital energy levels. Table 2 shows that both the HOMO and LUMO energy levels decrease with increasing electric field. Simultaneously, the band gap E of the EPDM molecular chain... G The band gap decreases from 9.408 eV to 4.432 eV. Overall, the reduced band gap lowers the energy required for electrons to transition to higher energy levels, making chemical reactions easier. When the applied voltage is sufficiently high, the energy imparted enhances the escape ability of trapped charges, disrupting the polarization equilibrium and causing the release of polarization energy, leading to the emission of a large number of electrons and photons. The gas adsorbed on the material surface absorbs the released energy and ionizes, producing more electrons and thus intensifying the surface discharge process.

[0049] Table 2. Variation of EPDM molecular frontier orbital energy levels with electric field.

[0050] Table 2Change of frontier orbital energy level of EPDM molecule with electric field

[0051]

[0052] Figure 4 The top image shows the LUMO orbital, and the bottom image shows the HOMO orbital. With increasing electric field, the HOMO orbital contour map shifts to the left end of the chain, while the LUMO orbital contour map is distributed around the third monomer and is below the LUMO orbital energy level in the absence of an electric field. Therefore, this region is prone to becoming an electron trap, and the nucleophilic activity in this region increases, making the accumulated electrons relatively more reactive. Furthermore, the distances between the HOMO and HOMO-1 orbitals, and between the LUMO and LUMO+1 orbitals, are observed to decrease, indicating a shallower trap energy level.

[0053] Step 3: Calculate and analyze the molecular trap depth and density of states. Due to the harsh operating environment of EPDM cables, contact with air and moisture is inevitable during actual operation, leading to unavoidable changes and aging of the insulation structure. During the oxidation process of EPDM, the CH bonds are easily broken, and -OOH groups are present in the reaction. Therefore, a model of the EPDM molecule during oxidation was established, and its structure was optimized and energy was calculated. The model is as follows: Figure 5 As shown. The calculation results are shown in Table 3, where E... EA (1) E represents the electron affinity without defects. EA (2) E represents the electron affinity after the defect is generated. trap The depth of the space charge trap.

[0054] Table 3 Trapping depth of EPDM molecules under electric field.

[0055] Table 3Trap depth of EPDM molecules under electric field

[0056]

[0057] As shown in Table 3, the trap depth of EPDM single-chain molecules decreases from 0.740 eV to 0.043 eV with increasing electric field. Possible reasons for this change include: EPDM is an amorphous material; when subjected to an external electric field, the Maxwell stress generated internally alters its microstructure, causing irregularly arranged molecular chains to undergo localized ordered arrangement, reducing structural physical defects and thus shallowing the trap energy levels. Simultaneously, the dielectric barrier tilts under an external electric field. Even if the energy required for charge escape does not reach the threshold energy, a small amount of charge is always excited to the conduction band due to the tunneling effect, which is equivalent to the EPDM trap energy level becoming shallower under the influence of an electric field. Therefore, when molecules are subjected to an external electric field, their internal charge distribution changes, leading to a shallower space charge trap depth, making it easier for electrons to escape and promoting discharge generation.

[0058] To better understand the trap states of EPDM molecules, density of states diagrams were plotted under both electric and non-electrical conditions, such as... Figure 6 As shown, after the band gap narrows, the peak appears around the HOMO and LUMO levels. Its value is lower and its width is narrower compared to other peaks, indicating the appearance of some localized states. These localized states near the HOMO and LUMO levels can be considered as introducing hole traps and electron traps, respectively. Overall, the addition of an electric field increases the number of traps compared to the absence of an electric field, having a greater impact on carrier trapping and detrapping. For shallow traps, it helps increase the number of discharges.

[0059] Step 4: Plot and analyze the electrostatic potential distribution on the molecular surface. Using Multiwfn 3.8 software and the visualization program VMD 1.9.3, the three-dimensional electrostatic potential field on the EPDM molecular surface was plotted for F = 0.000au and F = 0.008au, as shown below. Figure 7(a) , 7(b) As shown, the blue and red areas and the green and orange spheres represent the negative electrostatic potential, positive electrostatic potential, minimum electrostatic potential, and maximum electrostatic potential, respectively. It can be seen that when the electric field is zero, there are more maxima than minima around the third monomer, exhibiting overall nucleophilicity. Nucleophilicity attracts electrons to move towards the third monomer region, forming electron traps. After applying an electric field, charges move, and the positive and negative electrostatic potentials redistribute. The negative electrostatic potential is smaller on the front and back sides of the carbon-carbon double bond, and the negative electrostatic potential on the back side reaches a minimum value of -71.94 kJ / mol. Electrophilic reactions easily occur here, making electrons more active in the third monomer region. Because there are air gaps between the ethylene propylene rubber material and the surrounding air molecules, the large number of active electrons in the third monomer easily cause ionization in these air gaps, exacerbating the development of electron avalanche.

[0060] Step 5: Calculate excited states and plot UV-Vis absorption spectra. Based on the optimized EPDM molecular ground state structure, the first 50 excited states under various electric field intensities were calculated using the TD-DFT / / M06-2X / 6-31g(d) method, and UV-Vis absorption spectra were plotted.

[0061] Table 4 only shows a portion of the excitation energies; under the influence of an external electric field, the excitation energy generally shows a decreasing trend. This indicates that an increase in the electric field makes EPDM molecules increasingly easier to excite. The initial excitation energies for water vapor, oxygen, and nitrogen in the air are 7.6 eV, 7.9 eV, and 6.1 eV, respectively. When the electric field increases to a certain level, electrons in EPDM molecules only require a small amount of energy to be excited. After the energy of the photons released by the excitation is absorbed by these gas molecules, the probability of ionization of electrons inside the gas increases. This gas ionization will lead to the generation of effective initial electrons.

[0062] Table 4. Variation of excitation energy of partially excited states of EPDM molecules under the influence of an electric field.

[0063] Table 4Changes of excitation energy of partially excited state ofEPDM molecule under electric field

[0064]

[0065] Figure 8 The UV-Vis absorption spectra of EPDM molecules under different electric fields are shown. In the absence of an electric field, EPDM molecules exhibit two absorption peaks at 119.41 nm and 174.99 nm. The absorption peak at 119.41 nm is mainly contributed by the excited states S0→S50 (18.03%), S0→S30 (10.54%), and S0→S40 (7%). The absorption peak at 174.99 nm is contributed by S0→S1 (99.96%). When the electric field is increased to 0.008 au, only one absorption peak appears at 176.15 nm, contributed by the electronic transition S0→S37 (99.83%). It can also be seen that the two absorption peaks exhibit different degrees of redshift with increasing electric field.

[0066] Step 6: Plot charge transfer spectra and perform hole-electron analysis on the relevant excited states. Charge transfer spectra were plotted using Multiwfn 3.8 software, as shown below. Figure 9(a) , 9(b) As shown. Here, it is assumed that the EPDM molecule is divided into three segments, with segments 1, 2, and 3 corresponding to the ethylene chain, propylene chain, and the third monomer ENB, respectively. Figure 9(a) , 9(b)It can be seen that the absorption peak at 119.41 nm when the electric field is 0 is jointly determined by the electron redistribution within both the propylene and third monomer fragments, as well as the electron transfer between the two fragments, and their contributions are not significantly different. The absorption peak at 174.99 nm, however, is mainly caused by electron excitation within the third monomer region. Similarly, the absorption peak at 176.15 nm when the electric field is 0.008 au is also primarily caused by electron excitation within the third monomer region.

[0067] Analysis of the EPDM UV spectra at electric fields of 0 a.u. and 0.008 a.u. revealed that the transitions were primarily caused by ground state transitions to excited states 1, 30, 37, 40, and 50. Therefore, hole-electron analysis was performed on these five singlet excited states using Multiwfn 3.8 software, and orbital transition diagrams were plotted, as shown below. Figure 10 As shown in the figure, the blue and green parts represent the hole and electron distributions, respectively. The relevant excited-state parameters are shown in Table 5, where the Sr parameter is the geometric mean of the hole-electron overlap, the D parameter is the hole-electron centroid distance, and the t parameter is the hole-electron separation.

[0068] Table 5. Parameters of each excited state under different external electric fields.

[0069]

[0070] Combination Figure 10 As shown in Table 5, in the absence of an electric field, the hole and electron orbitals in S0→S1 are mainly composed of MO122 (HOMO) and MO123 (LUMO), respectively, with an Sr exponent of 0.851, a small D exponent, and a significantly negative t exponent. When the electric field is 0.008 au, the hole orbitals in S0→S37 become dominated by MO104, and the D exponent changes to... A negative t-exponent indicates, in the distribution space, a high degree of overlap between the hole and electron distributions of the two excited states, suggesting insufficient separation and binding. Figure 10 It can be determined that all are localized excitations of C=C bond π orbitals → C=C bond π* orbitals. The Sr exponents of the excited states S0→S30, S0→S40, and S0→S50 are similar, and the t exponents are all negative. However, the D exponent is larger in S0→S40, indicating that the distance between the electron and hole mass centers is greater at this time. Although there is no significant separation between electrons and holes, according to... Figure 10The excitation from S0 to S40 is determined to be a unidirectional charge transfer excitation of the σ orbital of the 43C-60C bond → the π* orbital of the C=C bond. It can be observed that the hole distribution exhibits σ characteristics from S0 to S30, and both σ and π orbital characteristics from S0 to S50. The local excitation from S0 to S30 is identified as the σ orbital of the C=C bond → the π* orbital of the propylene fragment CC bond, and the σ orbital of the cyclic structure → the π* orbital of the cyclic structure → the π* orbital of the C=C bond → the π* orbital of the C=C bond.

[0071] The above analysis shows that the third monomer fragment is the main electronic excitation region. The holes and electrons in each excited state are close to each other and have low spatial separation. This state is conducive to the recombination of holes and electrons, thereby causing the emission of photons.

[0072] This invention calculates the accurate space charge trap depth using electron affinity and the density of states, which can represent the trap density and fully represent the trap states under an electric field. Calculations of infrared spectra show that molecular chains break under an electric field, proving that free radicals are generated under a sustained electric field. Calculations of ultraviolet spectra yielded the most contributing excited states, which will be used for further research. Calculations of charge transfer spectra provide a direct view of charge transfer within the molecular chain, revealing charge transport information.

[0073] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for analyzing the influence of the microscopic properties of ethylene propylene diene monomer (EPDM) rubber molecules on surface discharge, characterized in that, Includes the following steps: Step 1: Construct an ideal molecular chain model based on the actual production ratio of EPDM rubber; Step 2: The initial EPDM rubber molecule was optimized and its frequency was calculated using density functional theory, resulting in a more accurate and lowest-energy optimized model of the EPDM rubber molecule. Step 3: The influence of the microstructure of EPDM rubber on surface discharge under an electric field is analyzed by examining the ground-state microstructure of molecular geometry, infrared spectroscopy, dipole moment, orbital energy level, space charge trap depth, density of states, and ground-state electrostatic potential of the molecular surface. Step 4: Calculate the excitation energy, UV-Vis absorption spectrum, charge transfer spectrum, and hole-electron excited-state microstructures of EPDM rubber molecules using time-dependent density functional theory, and analyze the influence of the microstructures of EPDM rubber on surface discharge under an electric field. The space charge trap depth is expressed as the electron affinity of the molecular system before defects are generated minus the electron affinity after defects are generated; Electron affinity (EEA) is the energy difference generated when an optimized neutral molecule gains electrons to become an anion, as shown in equation (1): ； （1） in E ( N ), E ( N+1 These represent the energies of neutral molecules and anion molecules, respectively. The surface electrostatic potential of molecules reflects the movement of charges and provides information on molecular reactivity, as shown in equation (2): ；（2） in, V ( r ) indicates the position r The electrostatic potential at that point is determined by the atomic nucleus. V nuc ( r ) and electronic V ele ( r Joint contribution, Z A It is the nuclear charge of atom A. R A The nuclear coordinates of atom A. ρ ( r' () represents electron density; The expression for the charge density of holes and electrons is defined as follows: ；（3） ；（4） In the formula, is r Coordinate vector; ρ hole ( r )and ρ ele ( r ) represent hole density distribution and electron density distribution, respectively. Both are divided into two parts: local term loc and cross term cross. The charge transfer spectrum is based on the idea of ​​charge transfer between segments. Assuming that the molecule is divided into several segments, the total UV-Vis absorption spectrum is decomposed into different sub-curves from the perspective of charge transfer between segments. In this way, the transfer of charge between segments can be directly and clearly seen. Therefore, the absorption curve of electron transfer from segment A to segment B can be expressed as Equation (5): ；（5） in E (λ) Indicates absorption wavelength λ The corresponding energy, i Summing over each excited state, f It is the strength of the oscillator. Q i A,B It is the number of electrons transferred from A to B. E i exc It is excitation energy. G It is a broadening function.

2. The method for analyzing the influence of the microscopic properties of EPDM rubber molecules on surface discharge according to claim 1, characterized in that, The actual production ratio of the EPDM rubber is ethylene, propylene and a third monomer polymerized in a ratio of 5:4:

1.

3. The method for analyzing the influence of the microscopic properties of EPDM rubber molecules on surface discharge according to claim 1, characterized in that, The structural optimization and frequency calculation employ the M06-2X functional and the 6-31g(d) basis set from density functional theory.

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