A molecular simulation method for the electron beam irradiation and heating coupled pre-oxidation process of polyacrylonitrile fibers

Abstract

This invention provides a molecular simulation method for the pre-oxidation process of polyacrylonitrile fibers coupled with electron beam irradiation and heating, comprising the following steps: establishing a trans-syndiotactic stereotype model of polyacrylonitrile under a specific oxygen environment using computer molecular materials simulation software; inserting a temperature controller and creating a primary collision atom bombardment molecular system during the gradient heating process of polyacrylonitrile pre-oxidation using molecular dynamics methods to simulate the coupling effect of irradiation and heating; continuing the gradient heating to complete the molecular dynamics simulation of pre-oxidation; and outputting the microscopic results of the simulation process. This invention uses molecular dynamics methods to introduce electron beam irradiation during the gradient heating process of polyacrylonitrile to simulate the coupling effect of electron beam irradiation and heating in the pre-oxidation process of polyacrylonitrile. It proposes a set of controllable simulation parameters for the timing of electron beam irradiation introduction during the pre-oxidation process, which has guiding significance for exploring the pre-oxidation reaction mechanism of the coupling effect of electron beam irradiation and heating on polyacrylonitrile fibers.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and carbon fiber processing, specifically relating to a molecular simulation method for the pre-oxidation process of polyacrylonitrile (PAN) fibers coupled with electron beam irradiation and heating. This technique aims to simulate the effect of electron beam irradiation and heating coupling on the PAN molecular chain during the pre-oxidation process by establishing a trans-syndiotactic stereopolyacrylonitrile (PAN) model. Background Technology

[0002] PAN-based carbon fibers are widely used in aerospace, electronics, medical, and sports fields due to their low density, high strength, and high rigidity. Compared to other precursors such as cellulose and pitch already used in commercial fibers, PAN-based carbon fibers support over 90% of commercial carbon fiber production due to their superior mechanical properties. The pre-oxidation process of PAN-based carbon fibers is a crucial step in determining the final carbon fiber properties, directly affecting the quality of the final fibers produced by subsequent carbonization and graphitization. The high cost and time-consuming nature of the pre-oxidation process under PAN experimental conditions has always been a major challenge for the carbon fiber industry.

[0003] In the study of PAN irradiation pre-oxidation process, the literature on the high-dose-rate electron beam irradiation effect of polyacrylonitrile fibers and its influence on pre-oxidation uses the change in free radical concentration during the pre-oxidation process as a reference to optimize the pre-oxidation process of electron beam irradiation modified PAN fibers; the literature on microfocus SR-SAXS reconstruction and molecular simulation revealing the heterogeneous microstructure of γ-irradiated pre-oxidized PAN fibers uses molecular simulation to depict the structural evolution of different PAN structures after heat treatment and the introduction of irradiation; the literature on the molecular simulation of stabilization of PAN-based carbon fiber processing uses a model combining stochastic chemical reactions and molecular dynamics to simulate the PAN heat treatment process at atomic detail; the literature on the molecular simulation of microstructure evolution during carbon fiber processing uses the ladder-like chain structure of PAN to simulate the microstructure evolution during carbonization and graphitization of PAN-based carbon fibers; in PAN modeling research, molecular dynamics studies of the crystalline and pseudocrystalline phases of polyacrylonitrile indicate that PAN molecular chains have relatively complex chain structures such as random, syndiotactic, and isomorphic structures, while the syndiotactic structure of PAN with a planar "zigzag" conformation has the lowest energy and the highest stiffness among all chain conformations, and is one of the most promising conformations.

[0004] Current research is limited to PAN irradiation pre-oxidation processes or pre-oxidation processes involving irradiation followed by heat treatment. There is a lack of molecular dynamics simulation techniques using PAN chain models to couple irradiation and heating during pre-oxidation. Furthermore, introducing electron beam irradiation during PAN gradient heating remains a challenge that cannot be addressed under laboratory conditions. Therefore, combining molecular dynamics simulations with the PAN trans-syndiotactic stereostructure model and the coupling of electron beam irradiation and heating for pre-oxidation can help explore the optimal timing for introducing electron beam irradiation into PAN fibers during heat treatment. This is of great significance for optimizing the pre-oxidation process of PAN fibers involving the coupling of electron beam irradiation and heating. Summary of the Invention

[0005] This invention provides a modeling method for a low-energy, high-stiffness planar zigzag inverse syndiotactic stereochemical molecular chain model of PAN. The model is then used in the Lamps dynamic simulation tool for pre-oxidation simulation calculations involving irradiation and heating coupling. During the PAN heat treatment process, a temperature controller is used, and electron beam irradiation is introduced, followed by simulation calculations and output. Molecular dynamics methods are used to predict the influence of irradiation-heat coupling on the pre-oxidation process and structural evolution of PAN fibers, filling the gap in molecular dynamics simulation technology for the pre-oxidation of PAN precursor fibers, from establishing an inverse syndiotactic stereochemical model to the pre-oxidation process involving electron beam irradiation and heating coupling.

[0006] In summary, the present invention adopts the following technical solution:

[0007] A molecular simulation method for a pre-oxidation process of polyacrylonitrile fibers coupled with electron beam irradiation and heating includes the following steps:

[0008] (1) Using MaterialsStudio software, draw a PAN monomer, and use the Build Polymers module to select the head and tail atoms to create a repeating unit formed by connecting two PAN monomers.

[0009] (2) Using MaterialsStudio software, the PAN dimer was used as a new monomer molecule, and the degree of polymerization was set to establish a trans-syndiotactic molecular chain.

[0010] (3) Introduce the molecular chain obtained in step (2), and use the Movement module of Materials Studio software to replicate and combine the molecular chain. Based on the hexagonal lattice chain stacking mode of PAN, and according to the experimental density of PAN of 1.17-1.20 g / cm³, 3 This creates an ideal inverse syndiotactic stereostructure PAN hexagonal unit cell model.

[0011] (4) Introduce the hexagonal cell model obtained in step (3), and use the Crystal module in MaterialsStudio software to build a rectangular Amorphous Cell box with chain length * width * height. Place the already built PAN hexagonal cell model in the box and add a certain number of oxygen molecules.

[0012] (5) Export the three-dimensional coordinate data file of the model in step (4) and convert the file format;

[0013] (6) Using the Lammps software, import the data file obtained in step (5), set the simulation parameters, select the reactive force field, first perform energy minimization, then position constraint, and finally relaxation, so that the whole system reaches the initial equilibrium state.

[0014] (7) Using the Lammps software, introduce the stable structure obtained in step (6), set the gradient heating range and simulation parameters, perform gradient heating simulation, and output various data files during the simulation system operation.

[0015] (8) Using the Lammps software, a PKA location region is created during the gradient heating process. The kinetic energy of PKA in the x, y, and z directions is set according to the irradiation dose to simulate the irradiation energy transfer. The kinetic energy of PKA is monitored, irradiation simulation is performed, and various data files are output during the simulation system calculation process.

[0016] (9) Using the Lammps software, import the three-dimensional coordinate data after irradiation obtained in step (8), continue to perform gradient heating, and output the simulation system conformation and various data files.

[0017] (10) Visualize and verify the simulation results obtained in steps (8) and (9), output the simulation flowchart, and perform species number and molecular weight statistics on the simulation process.

[0018] The conversion software used in step (5) is OVITO visualization software.

[0019] The energy minimization algorithm used in step (6) is the conjugate gradient method, and the relaxation method is the Nosé-Hoover thermostat method. The relaxation uses a canonical (NVT) ensemble, and the simulation duration is 20 ps.

[0020] The simulation parameters mentioned in step (6) include simulation environment parameter settings, using a charge balancing algorithm to dynamically adjust atomic charges in the simulation to meet the balance of charge distribution;

[0021] In step (7), the gradient heating range is selected from a pre-oxidation temperature of about 300K to 600K. A heating gradient is set and a heating and holding process is performed. A canonical (NVT) ensemble is used, and the simulation time for each temperature gradient is 10ps.

[0022] In step (8), a microcanonical ensemble (NVE) is used, and a Berendsen temperature controller is used to control the temperature range. The simulation duration is set according to the irradiation dose and PKA kinetic energy.

[0023] Step (8) Monitor the kinetic energy of PKA, use the “compute” command in combination with the “variable” command to calculate the total kinetic energy of PKA, and then output the kinetic energy of PKA.

[0024] The conformations described in steps (7) and (8) are viewed using OVITO software.

[0025] The PKA kinetic energy expression obtained in step (8) is as follows:

[0026]

[0027] Here, we assume that the velocity v is along the direction [h, k, l], the kinetic energy is NeV, and the mass is M gram / mol, N A is Avogadro's constant.

[0028] Step (10) Take a simulation snapshot using OVITO software to obtain simulation details, and use Python software to count the number of species and molecular weight in the species files output by the simulation process.

[0029] This invention studies a complete simulation method for the pre-oxidation process of PAN fibers, which involves the introduction of electron beam irradiation during the modeling and heat treatment stages. Through molecular dynamics simulation, it solves the problem of exploring the pre-oxidation process of PAN fibers under current traditional experimental conditions by investigating the coupling effect of irradiation and heating.

[0030] By controlling the electron beam irradiation dose and irradiation introduction time, molecular dynamics simulation of the microscopic reaction of PAN precursor fibers under electron beam irradiation conditions during gradient heating was achieved. This led to the optimization of irradiation dose and temperature parameters for the coupling of electron beam irradiation and heating in PAN fibers, and the exploration of the optimal timing for introducing electron beam irradiation into trans-syndiotactic PAN fibers during heat treatment. This provides in-depth theoretical basis and support for the pre-oxidation process of PAN fiber irradiation and heating coupling. Attached Figure Description

[0031] Figure 1 It is a PAN dimer defined as having head and tail atoms in Example 1.

[0032] Figure 2It is the trans-syndiotactic PAN chain with a degree of polymerization of 60 in Example 1.

[0033] Figure 3 This is the PAN hexagonal lattice chain packing diagram in Example 1.

[0034] Figure 4 This is the initial structure diagram of the PAN hexagonal unit cell in Example 1.

[0035] Figure 5 This is a flowchart of the pre-oxidation process of introducing electron beam irradiation in the early stage of the PAN model heat treatment in Example 1.

[0036] Figure 6 This is a molecular weight diagram showing the results of electron beam irradiation pre-oxidation of PAN during the initial stage of heat treatment in Example 1.

[0037] Figure 7 It is the trans-syndiotactic molecular chain of the ternary copolymer PAN with a degree of polymerization of 100 in Example 2.

[0038] Figure 8 This is the initial structure diagram of the hexagonal unit cell of the ternary copolymer PAN trans-syndiotactic stereostructure in Example 2.

[0039] Figure 9 This is a flowchart of the pre-oxidation process of introducing electron beam irradiation in the later stage of the PAN model heat treatment in Example 2.

[0040] Figure 10 This is a molecular weight diagram showing the results of electron beam irradiation pre-oxidation of PAN during the later stage of heat treatment in Example 2. Detailed Implementation

[0041] The specific technical solution of the present invention will be illustrated with examples.

[0042] Example 1

[0043] The first embodiment of the present invention provides a molecular simulation method for a pre-oxidation process of polyacrylonitrile fibers coupled with electron beam irradiation and heating, the method comprising the following steps:

[0044] (1) Using the software MaterialsStudio, based on the planar zigzag configuration of the PAN monomer molecule and the structure of all trans conformations, the probability of the reaction of the two monomer molecules is determined to be 0.5 each.

[0045] (2) Use the software MaterialsStudio to create a PAN monomer, use the Build Polymers module to select the head and tail atoms, create a repeating unit with two monomers, form a trans chemical bond connection site, and connect the two monomers into a dimer.

[0046] Figure 1It is a PAN dimer defined as having head and tail atoms in Example 1.

[0047] (3) Using the software MaterialsStudio, the dimer is regarded as a new monomer. Using the Buid Polymers module, this dimer is a new monomer molecule. The degree of polymerization is set to 30, that is, each molecular chain has 60 monomers.

[0048] Figure 2 It is the trans-syndiotactic PAN chain with a degree of polymerization of 60 in Example 1.

[0049] (4) Using Materials Studio software, the molecular chain described in step (3) was replicated. Based on the hexagonal lattice packing of polyacrylonitrile, the PAN interchain spacing formula a = √3b was obtained. Based on the experimental density of 1.17~1.22 g / cm³, the molecular chain was replicated. 3 The spacing between molecular chains in the hexagonal unit cell model was determined to be... Construct a hexagonal PAN simulation box;

[0050] Figure 3 This is the PAN hexagonal lattice chain packing diagram in Example 1.

[0051] Step (4) The size of the PAN hexagonal unit cell simulation box is 12.5×12.5×9nm. 26 oxygen molecules are added to the simulation box to simulate an environment with a 21% oxygen concentration. The resulting simulation system is converted into a three-dimensional coordinate file that can be recognized by dynamic simulation calculation tools.

[0052] Figure 4 This is the initial structure diagram of the PAN hexagonal unit cell in Example 1.

[0053] (5) Using the Lammps software, import the initial three-dimensional coordinate file obtained in step (4), set the simulation unit to real units, the x, y, and z directions to periodic boundary conditions, the atom type to charge, and the simulation time step to 0.25fs;

[0054] (6) Using the Lammps software, select the reactive force field, specify the types of elements used in the simulation, including hydrogen, carbon, nitrogen and oxygen elements, and output thermodynamic information every 100 steps to monitor the system status.

[0055] In step (6) of the reactive force field parameters, a charge balance algorithm is used. This algorithm is suitable for dynamically adjusting atomic charges in the reactive force field simulation to meet the balance of charge distribution.

[0056] (7) Using the Lammps software, the “variable” command was used to redefine the model area in the x, y, and z directions of the simulation box, and the “fix” command was used to constrain the position of the two ends of the model, fixing the force at both ends to 0, and performing energy minimization calculation.

[0057] The energy minimization algorithm used in step (7) is the conjugate gradient method, and the damping value is set to 5000.

[0058] (8) Initial relaxation was performed at 300K to obtain a stable configuration;

[0059] The relaxation described in step (8) is the Nosé-Hoover thermostat method. The relaxation uses NVT, the simulation duration is 40 ps, ​​and the neighbor list is updated every 100 steps.

[0060] (9) Using the Lammps software, the stable configuration obtained in step (8) is introduced, and six temperature gradients are set, namely 498K, 528K, 548K, 568K, 580K and 598K. Electron beam irradiation simulation is introduced in the first gradient heating stage from 300K to 498K.

[0061] (10) Using the Lammps software, the initial position region of PKA was created using the "create_atoms" and "region" commands, and the coordinates were set to (40, 2, 67). The oxygen atom was set as PKA, and the kinetic energy of its x, y, and z directions was set using the "velocity" command according to the irradiation dose to simulate the irradiation energy transfer. At the same time, the kinetic energy of PKA was monitored and the simulation data file was output.

[0062] In step (10), the oxygen atom is given kinetic energy according to the PKA electron volt-kinetic energy conversion formula. Here, the "velocity" command is used to set the kinetic energy in the y-direction to be... Perform dynamic calculations and use the "dump" command to output files of type species, bond, dump, xyz, and data.

[0063] In step (10), the “compute” command is used to define the PKA velocity components, and the “variable” command is used to sum the squares of each velocity component. Then, the “compute reduce” command is used to obtain the sum of squares. Finally, the “variable” command is used to calculate the total kinetic energy of the PKA. The output is performed every 100 steps to monitor the change in PKA kinetic energy.

[0064] In step (10), NVE is used, and the temperature during irradiation is adjusted to 300K-498K using a Berendsen temperature controller. The time scale of the temperature controller is set to 2000 steps, and the heat dissipation is slowly consumed. The irradiation simulation duration is 100ps.

[0065] (11) Using the Lammps software, import the data file obtained in step (10) and continue processing the 498K, 528K, 548K,

[0066] (11) Using the Lammps software, import the data file obtained in step (10), and continue to perform heating and heat preservation treatment on each stage of 498K, 528K, 548K, 568K, 580K and 598K, and output species, bond, dump and xyz data files;

[0067] In step (11), the NVT ensemble is used again, and the simulation duration for each temperature gradient heating and holding is 10ps.

[0068] The total simulation duration is 230ps.

[0069] In step (11), during the simulation of each gradient heating and holding process, the output file can be verified and analyzed using OVITO software, thereby obtaining the molecular-level reaction image of the trans-syndiotactic stereotype PAN model during the pre-oxidation process, and performing image analysis.

[0070] Figure 5 This is a flowchart of the pre-oxidation process of introducing electron beam irradiation in the early stage of the PAN model heat treatment in Example 1.

[0071] (11) Import the species file output in step (10) and use Python software to perform species and molecular weight analysis on the final output heat treatment data;

[0072] Figure 6 This is a molecular weight diagram showing the results of electron beam irradiation pre-oxidation of PAN during the initial stage of heat treatment in Example 1.

[0073] Example 2

[0074] The second embodiment of the present invention provides a molecular simulation method for the pre-oxidation process of polyacrylonitrile fibers coupled with electron beam irradiation and heating. This embodiment differs from the first embodiment in that, to verify its beneficial effects, comparative data on the coupling effect of electron beam irradiation and post-heat treatment in the present invention are provided. The method includes the following steps:

[0075] (1) Using the software MaterialsStudio, based on the trans conformation of the planar "zigzag" PAN trans syndiotactic stereostructure, a PAN monomer is established, and the connection sites between monomers are determined.

[0076] (2) Using the software MaterialsStudio, select the head and tail atoms using the Build Polymers module to connect two monomers into a dimer, forming a trans chemical bond connection site. Use this dimer as a new monomer and set the degree of polymerization to 50, that is, each molecular chain has 100 PAN monomers.

[0077] (3) Using the software MaterialsStudio, a copolymer was added to the trans-syndiotactic PAN chain with a degree of polymerization of 100, and two methyl acrylate monomers and three itaconic acid monomers were added.

[0078] Figure 7 It is the trans-syndiotactic molecular chain of the ternary copolymer PAN with a degree of polymerization of 100 in Example 2.

[0079] (4) Using MaterialsStudio software, the molecular chains described in step (3) are copied and combined to determine the spacing between the molecular chains in the hexagonal unit cell model. Construct a PAN (polyhedral lattice) simulation box;

[0080] Step (4) The size of the hexagonal PAN simulation box is 21.5×21.5×12nm. 84 oxygen molecules are added to the simulation box to simulate a 21% oxygen environment. The resulting simulation system is converted into a three-dimensional coordinate file that can be recognized by dynamic simulation calculation tools.

[0081] Figure 8 This is the initial structure diagram of the hexagonal unit cell of the ternary copolymer PAN trans-syndiotactic stereostructure in Example 2. The three-dimensional coordinate transformation software is OVITO software.

[0082] (5) Using the Lamps software, the initial three-dimensional coordinate information obtained in step (4) is introduced, the simulation unit is set to real units, the x, y, and z directions are periodic boundary conditions, the atom type is charge, and the simulation time step is 0.25fs;

[0083] (6) Using the Lammps software, select the reactive force field and specify the types of elements used in the simulation, including hydrogen, carbon, nitrogen and oxygen. Output thermodynamic information every 100 steps to monitor the system status.

[0084] (7) Using the Lammps software, the “fix” command is used to constrain the position of the two ends of the model, fix the force at both ends to 0, and perform energy minimization calculation.

[0085] (8) Initial relaxation was performed at 300K to obtain a stable configuration;

[0086] The energy minimization algorithm used in step (7) is the conjugate gradient method, and the damping value is set to 10000.

[0087] The relaxation method described in step (8) is the Nosé-Hoover thermostat method. The relaxation uses NVT, the simulation duration is 20 ps, ​​and the neighbor list is updated every 100 steps.

[0088] (9) Using the Lammps software, import the relaxation data file obtained in step (8) and use the "fix" command to perform gradient heating.

[0089] Step (9) Select a temperature range of 300K-583K and set 7 temperature gradients of 463K, 483K, 503K, 523K, 543K, 563K and 583K respectively. Perform a temperature gradient heating and holding process for each temperature gradient. Use the "fix" command to heat the gradient to the 563K-583K stage. The simulation time for each gradient heating and holding is 10ps.

[0090] (10) During the 583K heat preservation stage, use the “create_atoms” and “region” commands to create 5 PKA initial position regions, set the coordinates as (30, 2, 65), (60, 2, 65), (108, 2, 65), (152, 2, 65), (183, 2, 65) respectively, set oxygen atoms as PKA, use the “velocity” command to set the kinetic energy of primary collision atoms in the x, y, and z directions according to the irradiation dose to simulate irradiation energy transfer, and monitor the kinetic energy of PKA and output irradiation data files at the same time;

[0091] Step (10) assigns kinetic energy to oxygen atoms to simulate irradiation energy. Five PKAs are used to componentize the incident particle energy. Here, the "velocity" command is used to set the kinetic energy in the y-direction of each primary collision atom to be [value missing]. Perform dynamic calculations and use the "dump" and "fix" commands to output species, bond, dump, and xyz data files.

[0092] In step (10), the “compute” command is used to define the PKA velocity components, and the “variable” command is used to sum the squares of each velocity component. Then, the “compute reduce” command is used to obtain the sum of squares. Finally, the “variable” command is used to calculate and output the total kinetic energy of the PKA. The time step is once every 100 steps.

[0093] In step (10), NVE is used, and the temperature is controlled at 583K-583K using a Berendsen temperature controller to gradually dissipate the irradiated heat. The time scale of this temperature controller is set to 1000 steps to slowly dissipate the heat, and the irradiation simulation duration is 20ps.

[0094] The total simulation duration is 170ps.

[0095] In step (10), during the gradient heating and heat preservation process, the simulation process can be verified and analyzed using OVITO software to obtain molecular-level reaction images of trans-syndiotactic PAN during the pre-oxidation process.

[0096] Figure 9 This is a flowchart of the pre-oxidation process of introducing electron beam irradiation in the later stage of the PAN model heat treatment in Example 2.

[0097] (11) Introduce the species file output in step (10) and use Python software to perform statistical analysis on the species and molecules of the final output heat-processed data.

[0098] Figure 10 This is a molecular weight diagram showing the results of electron beam irradiation pre-oxidation of PAN during the later stage of heat treatment in Example 2.

Claims

1. A molecular simulation method of a polyacrylonitrile fiber electron beam irradiation and heating coupled pre-oxidation process, characterized by, The method comprises the following steps: (1) using MaterialsStudio software, drawing a three-dimensional graph of polyacrylonitrile (PAN) monomer ball stick model, determining the PAN monomer connection site according to the molecular chain conformation of the trans syndiotactic body PAN, and setting the polymerization degree to establish the trans syndiotactic body molecular chain; (2) using MaterialsStudio software, establishing a hexagonal cell PAN simulation box according to the experimental density of PAN, adding a certain number of oxygen molecules in the simulation box to simulate the oxygen concentration condition, and converting the obtained model into a three-dimensional coordinate file recognizable by a dynamic simulation calculation tool; (3) using Lammps software, introducing the coordinate file obtained in step (2), setting simulation parameters, performing energy minimization operation and relaxation to obtain the stable configuration of the simulation system, and randomly distributing oxygen molecules in the simulation system; (4) using Lammps software, introducing the stable configuration obtained in step (3), restraining the positions of both ends of the model, setting a gradient temperature interval, inserting a temperature controller in the gradient temperature process, creating a primary knock-on atom (PKA) region, giving the PKA kinetic energy to simulate the energy transfer of irradiation, and performing simulation calculation and outputting simulation results; (5) using Lammps software, introducing the model data obtained in step (4), continuing to perform gradient temperature, and completing the pre-oxidation simulation; (6) visualizing the simulation process, and processing and analyzing the data file output by the simulation.

2. The molecular simulation method of the coupled electron beam irradiation and heating pre-oxidation process of polyacrylonitrile fibers according to claim 1, characterized in that In step (1), the head and tail atoms of the first monomer are polymerized to form a dimer, and the dimer is used as a new monomer molecule to establish the PAN trans syndiotactic body molecular chain. In step (2), a rectangular Amorphous Cell box is established using the Crystal module.

3. The molecular simulation method of the coupled electron beam irradiation and heating pre-oxidation process of polyacrylonitrile fibers according to claim 1, characterized in that In step (3), the energy minimization algorithm is the conjugate gradient method, and the relaxation algorithm is the Nosé-Hoover thermostat constant temperature method. In step (4), the temperature controller used is the Berendsen temperature controller.

4. The molecular simulation method of the coupled electron beam irradiation and heating pre-oxidation process of polyacrylonitrile fibers according to claim 1, characterized in that, In steps (3) and (5), the regular ensemble NVT is adopted, and in step (4), the microcanonical ensemble NVE is adopted. The force field selected is the reactive force field, and the simulation algorithm uses the charge equalization algorithm, which is suitable for dynamically adjusting the atomic charge in the reactive force field to balance the charge distribution: In step (3), the temperature is selected as 300K, and the simulation time is 20ps. In step (4), according to the pre-oxidation temperature, 5-7 temperature gradients are set, the PKA kinetic energy is set according to the irradiation dose and the PKA mass, and the irradiation simulation time is 20-100ps. In step (5), the gradient temperature is connected with the irradiation insertion temperature, and the gradient temperature simulation time is 90-130ps.

5. The molecular simulation method of the coupled electron beam irradiation and heating pre-oxidation process of polyacrylonitrile fibers according to claim 1, characterized in that, The expression of the PKA atomic kinetic energy is as follows: wherein the velocity is V, the velocity is assumed to be along the direction [h, k, 1], the kinetic energy is N, the kinetic energy unit is eV, the mass is M, the mass unit is gram / mol, N A is the Avogadro constant.

6. The molecular simulation method of the coupled electron beam irradiation and heating pre-oxidation process of polyacrylonitrile fibers according to claim 1, characterized in that In step (6), OVITO software is used to take atomic snapshots of the simulation process to obtain simulation details, and Python software is used to statistically analyze the molecular weight output by the simulation.

Images