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CN119446347B - A modeling and thermal conductivity optimization method for series-parallel semi-crystalline models of polymer materials - Google Patents

A modeling and thermal conductivity optimization method for series-parallel semi-crystalline models of polymer materials

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CN119446347B
CN119446347B CN202411250554.7A CN202411250554A CN119446347B CN 119446347 B CN119446347 B CN 119446347B CN 202411250554 A CN202411250554 A CN 202411250554A CN 119446347 B CN119446347 B CN 119446347B
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张宝玺
芮胜龙
张展翔
王翔
王江文
杨富辰
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Northwestern Polytechnical University
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Abstract

The invention provides a modeling and thermal conductivity optimization method for a polymer material serial-parallel semi-crystal model. Compared with a simple two-phase or three-phase series model, the method can better represent the relevant physical properties of the semi-crystalline polymer, has simple and convenient treatment and wide process applicability, and meets the design requirements of various semi-crystalline polymer models. Meanwhile, a treatment method for further improving the heat conduction performance of the semi-crystalline polymer model by utilizing an electric field is provided, and compared with the method for directly applying external force to cause the polymer to generate strain so as to improve the heat conduction performance, the method can better obtain the polymer material with excellent heat conduction performance on the premise of ensuring the mechanical property of the material force. The invention builds a polymer model under microscopic scale, reduces the experimental cost, fully utilizes the molecular dynamics method to explore the influencing factors of the heat conducting property of the polymer material, and improves the theory mechanism for preparing the high-performance radiator.

Description

Modeling and thermal conductivity optimization method for polymer material serial-parallel semi-crystal model
Technical Field
The invention belongs to the technical field of polymer material computer simulation, and particularly relates to a modeling method and a thermal conductivity optimization method of a polymer material serial-parallel semi-crystal model.
Background
With the vigorous development of aerospace technology, electronic components of the mounted equipment are developed to be highly integrated and miniaturized. With the rapid increase of circuit density and load capacity and the reduction of geometric dimensions, the heat dissipation of the structure is more difficult, and a large amount of generated heat is accumulated, so that the working performance and stability of the instrument and equipment are seriously affected. The '10 ℃ rule' in the electronic industry indicates that the failure rate of an electronic device is increased by one order of magnitude when the working temperature of the electronic device is increased by 10 ℃, and statistics shows that the failure of the electronic product caused by poor heat dissipation reaches 55%, which puts more severe requirements on the heat conduction performance of the heat management material. The heat generated by the integrated circuit in the electronic component is firstly transferred to the thermal interface material, then is dissipated to the external environment by the radiator through the electronic packaging material, the external thermal interface material and the high thermal conductivity material in a passive or active heat dissipation mode. Its primary dissipation path can be understood as being transferred in a well insulated thermal interface material. Therefore, the thermal conductivity of thermal interface materials must be improved to address the challenges faced by high performance chip thermal management systems.
In the field of material science today, polymer materials are attracting a great deal of attention due to their unique physical and chemical properties (insulation, high toughness, low density, low price, good corrosion resistance, etc.), and their thermal conductivity is a critical material property, which is of great importance for many applications, especially where a balance between thermal conductivity and insulation is required. However, the intrinsic thermal conductivity of the polymer material is low, which is about 0.1-0.5W/(m.K) at room temperature, so that the application of the polymer in the aspect of heat dissipation of electronic equipment is severely limited, and in addition, the application of the polymer-based thermal interface material is further limited due to the low contact thermal conductivity between the thermal interface material and a metal heterogeneous interface. Therefore, it is necessary to explore the thermal conduction mechanism of the thermal interface material with the polymer as the matrix, and provide a theoretical mechanism in microcosmic aspect for preparing the thermal interface material with high thermal conductivity.
In order to fully explore the influence mechanism of the heat conduction performance of the polymer-based material, asegun Henry et al in the paper Anomalous heat conduction in polyethylenechains: theory and molecular dynamics simulations published in the journal PHYSICAL REVIEW B, research the heat conduction performance of a single polyethylene chain, find the abnormal high heat conduction performance of a polyethylene single chain along the chain direction-300W/(m.K), and the intrinsic heat conduction of a far-ultra-polymer block, but only the ideal single chain polymer molecular chain is explored based on a theoretical and simulation method, and the influence factors of the heat conduction performance of the polymer block are not further explored. While Jun Liu et al in the paper "Tuning THE THERMAL conductivity ofpolymers WITH MECHANICAL STRAINS" published in the journal PHYSICAL REVIEW B "studied the effect of strain on the heat conduction properties of bulk amorphous polyethylene, found that with ordered arrangement of molecular chains within the polymer bulk, the heat conduction properties were improved by 5 times, but the direct application of strain would seriously affect the mechanical properties of the polymer material. In addition, jixiong He et al, journal of APPLIED PHYSICS, publication "Molecular dynamics simulation ofthermal transport in semicrystalline polyethylene:Roles of strain and thecrystallineamorphous interphase region" explored the effect of inter-chain coupling of crystalline and amorphous regions of an ideal series semi-crystalline polyethylene model on thermal conductivity by using a molecular dynamics simulation method, and found that the topology of the interlayer chain determines the dependence of thermal conductivity on strain. These studies have explored a part of the influencing mechanism of the heat conducting property of the polymer material on a microscopic scale by using a molecular dynamics simulation method. In addition, a local crystallization state exists in the polymer, and the current research on a semi-crystalline polymer model still stays in a two-phase or three-phase serial model, and a polymer model with serial-parallel characteristics still needs to be further researched.
Ferroelectric polymer-polyvinylidene fluoride (PVDF), which is a thermoplastic polymer composed of-CH 2CF 2-repeat units, this simple chemical structure gives a high degree of flexibility to its molecular chains, which can assume different molecular chain conformations and crystal structures under different conditions, and which has sensitivity to electric fields due to the CF2 groups contained therein. When an electric field is applied at a strength greater than the coercive electric field, the molecular segments change, as shown in fig. 1-2, which compress in the direction of the electric field and expand in the direction perpendicular to the electric field, having an electrostrictive effect. Based on the above, we can obtain PVDF with stretched molecular chains by controlling the coupling action of an electric field, and compared with other traditional polymer PVDF, the PVDF has the advantages of high temperature resistance, ageing resistance, good insulativity, high crystallinity and the like, so that the PVDF is an ideal thermal interface material matrix, and therefore we need to explore the influencing factors of the thermal interface material with PVDF as the polymer matrix, so as to improve the theory mechanism for preparing the high-performance radiator.
The research work of heat conduction influencing factors between the high heat conduction polymer-based thermal interface material and metal is important to realize global energy conservation and emission reduction, improve the energy utilization efficiency and solve the problem of electronic heat sealing.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provides a modeling and thermal conductivity optimization method for a polymer material series-parallel semi-crystal model.
In order to achieve the purpose, the technical scheme adopted by the invention is that the modeling and thermal conductivity optimization method of the polymer material serial-parallel semi-crystal model is characterized by comprising the following steps:
step 1, firstly, establishing a full-crystal polymer model with corresponding size according to the type of a required polymer;
Step 2, selecting a crystalline region of the central part as a permanent crystalline region according to the simulation requirement, taking other regions as temporary crystalline regions, and breaking interatomic covalent bonds between the permanent crystalline region and the temporary crystalline region;
Step 3, designating the main chain atom at the end of the molecular chain of the permanent crystalline region as R1, designating the main chain atom at the end of the molecular chain of the temporary crystalline region as R2, and then randomly forming covalent bonds between the R1 and the R2 atoms according to the simulation requirement to obtain a model I with different inter-chain coupling;
Step 4, using open source software Lammps as simulation software to simulate molecular dynamics of the model I to obtain a semi-crystalline polymer model with X, Y, Z directions conforming to the serial form, which is called serial-parallel semi-crystalline polymer model IV;
step 5, taking the model IV as an initial model, exploring the influence of an equal-intensity electric field applied in the X and Y directions on the form of the serial-parallel semi-crystalline polymer, and carrying out heat transfer analysis by using a non-equilibrium molecular dynamics method (NEMD) to obtain a change curve of temperature along with the position of each layer and a change curve of heat flow along with time;
And 6, respectively performing linear fitting on a temperature change curve along with each layer position and a heat flow change curve along with time through python software to obtain a temperature gradient value and a heat flow change rate along with time, and calculating the heat conductivity coefficient of the material according to a Fourier law to obtain the influence of the change of the electric field intensity on the heat conductivity of the polymer material.
Further, the 'permanent crystalline region' in step 2 is fully surrounded by the 'temporary crystalline region' to ensure the presence of amorphous polymer chains at the ends in the inter-chain direction or chain direction of the crystalline region during subsequent simulated localized melting.
In the step 3, the model I with different inter-chain couplings is obtained, the inter-chain couplings in the model I are set according to the simulation requirement, particularly, the judgment is carried out according to the bond length of the end atomic bonding, and the connection is not carried out when the distance exceeds the bond length, so that the unreasonable structure of the model I is prevented.
In step 4, open source software Lammps is used as simulation software to simulate the molecular dynamics of model I according to the following substeps:
(1) Predicting the size of the deformed polymer according to the model I, simulating the box, setting corresponding sizes, and enabling all model atoms to be positioned in the box to obtain a model II;
(2) Rendering color of the model II according to the sequence number of the molecular chain by ovito software visualization model, observing whether the division of the molecular chain of the polymer is correct or not, and correcting the molecular chain with wrong division so as to accurately extract the sequence number of the permanent crystalline region or determine the sequence number of the molecule at the later stage and further determine the sequence number of the atom by judging the z coordinate;
(3) The molecular chain serial numbers of the permanent crystalline region without inter-chain coupling between the molecular chains of the permanent crystalline region and the temporary crystalline region are recorded, and the atomic serial numbers in the permanent crystalline region with inter-chain coupling between the molecular chains of the permanent crystalline region and the temporary crystalline region are further determined through the coordinate positions;
(4) Setting potential functions describing interactions among atoms in a model II, and setting initial simulation conditions and parameters, wherein the set temperature is required to exceed the melting point of the crystalline polymer;
(5) For the potential function, if the interaction of long Cheng Kulun forces is considered, in order to avoid errors when an initial serial-parallel semi-crystalline polymer model is obtained, firstly, setting the interaction of the forces of length elimination Cheng Kulun is taken, and only the spatial position distribution of a molecular chain is considered for a model II at the beginning;
(6) After X, Y, Z three-direction boundary conditions are set as non-periodic boundary (f) conditions, in order to prevent polymer atoms from moving out of a simulation box in the process of local melting of a model II to cause simulation errors, reflecting walls are arranged on each surface of the simulation box;
(7) Carrying out local melting simulation on the model II by adopting a regular ensemble (NVT), fixing a permanent crystalline region ' through a simulation command when the ' temporary crystalline region ' is melted at a high temperature, and obtaining a model III after 1-2ns, wherein the permanent crystalline region still maintains a crystalline conformation, and the ' temporary crystalline region ' is converted into an amorphous state;
(8) Taking a model III as a model file, setting a long Cheng Kulun force interaction in a potential function, changing X, Y, Z three-direction boundary condition setting into a periodic boundary (p) condition, canceling a reflecting wall set in the substep (6) of the step 4, canceling the setting of a fixed permanent crystalline region in the substep (7) of the step 4, setting a simulation temperature below the melting point of a crystalline polymer, and avoiding structural damage of a subsequent crystalline region;
(9) Relaxation is carried out on the model III under isothermal and isobaric ensemble (NPT), and after 1-2ns, a semi-crystalline polymer model with X, Y, Z directions conforming to a serial form is obtained, and the semi-crystalline polymer model is called serial-parallel semi-crystalline polymer model IV;
in the substep (1) of the step 4, a symmetrically distributed vacuum layer is added to the model box to prevent more amorphous chains from being concentrated on one side.
In the substep (2) of the step 4, the observation of the polymer molecular chain is specifically that a model II file is opened in a text mode, a second column of data under Atoms is observed, and whether the molecular sequence number division is correct or not is judged by taking the total number of molecules conforming to the model as a standard.
In the substep (4) of the step 4, initial simulation conditions and parameters comprise model size, atom type, unit system, boundary conditions, neighbor list radius, time step, pressure and temperature, and the melting point of the crystalline polymer is determined according to literature or determined by utilizing Lammps to simulate a polymer heating process.
The substep (8) of step 4 further comprises performing the next simulation directly if the polymer chains are distributed in the simulation box, and narrowing the vacuum layer in the model file if the polymer chain clusters in the simulation box are around the 'permanent crystalline region' and have a larger vacuum layer, thereby preventing errors due to exceeding the long Cheng Kulun force interaction range when relaxing under isothermal and isobaric ensemble (NPT).
In the step 5, when the influence of the equal-intensity electric field on the form of the serial-parallel semi-crystalline polymer is explored in the X and Y directions, the intensity of the applied electric field does not exceed the value of the breakdown electric field intensity of the polymer, the simulation temperature is set above the melting temperature of the amorphous polymer and below the melting point of the crystalline polymer, after the electric field is applied, the model is cooled to the room temperature, and then the influence of the electric field with different intensities on the heat conducting performance of the model is measured.
In the step 5, the non-equilibrium molecular dynamics method specifically comprises the steps of dividing the model into N layers along the heat conduction direction, counting and outputting the temperature gradient of each layer under the stable heat flow, and calculating the heat conductivity by utilizing the Fourier law, wherein N is dependent on the length of the model and is more than or equal to 8.
The beneficial effects of the invention are as follows:
1. The invention provides a novel and more reasonable semi-crystalline polymer modeling method based on a molecular dynamics simulation method for the first time, namely a series-parallel semi-crystalline polymer model modeling method. The invention does not need complex model conformation treatment process, has simple and convenient treatment and wide process applicability, and meets the design requirements of various semi-crystalline polymer models.
2. Compared with a simple two-phase or three-phase serial model, the serial-parallel polymer simulation unit provided by the invention can better represent the relevant physical properties of the semi-crystalline polymer, and provides a new thought for exploring the influence mechanism of the physical properties of the polymer and the composite material thereof based on a molecular dynamic method under the subsequent microscopic scale.
Compared with the treatment method for further improving the heat conduction performance of the semi-crystalline polymer model by directly applying external force to cause the polymer to generate strain so as to further improve the heat conduction performance, the method can better obtain the polymer material with excellent heat conduction performance on the premise of ensuring the mechanical property of the material force. The invention builds a polymer model under microscopic scale, reduces the experimental cost, fully utilizes the molecular dynamics method to explore the influencing factors of the heat conducting property of the polymer material, and improves the theory mechanism for preparing the high-performance radiator.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a diagram of a model of a beta-type pure crystalline PVDF in an embodiment of the invention, wherein (a) is beta-type single cell of PVDF and (b) is a model after cell expansion;
FIG. 3 is a diagram of model I in an embodiment of the invention, the middle green part being the 'permanent crystalline region' and the remainder being the 'temporary crystalline region';
FIG. 4 is a color chart of model II rendering in an embodiment of the present invention, wherein (a) is a model chart with wrong molecular serial number, (b) is a model chart with corrected molecular serial number, and (c) is a model cross-sectional view with corrected molecular serial number;
FIG. 5 is a schematic diagram of a molten temporary crystalline region according to an embodiment of the present invention, wherein (a) is a schematic diagram of a direct molten state (b) is a cross-sectional view of a molten mold, and (c) is a schematic diagram of a vacuum layer after resizing;
FIG. 6 is a graph showing total energy versus relaxation time for an embodiment of the present invention;
FIG. 7 is a schematic diagram showing the model morphology change after the electric field is applied according to the embodiment of the present invention;
FIG. 8 is a cross-sectional view of a model after applying electric fields of different strengths of 2ns in accordance with an embodiment of the present invention;
FIG. 9 is a block diagram of a method of balancing molecular dynamics (NEMD) in accordance with an embodiment of the present invention;
FIG. 10 shows an embodiment of the present invention with an electric field strength of A time series-parallel connection semi-crystalline PVDF polymer model cold and heat source heat flow time-dependent diagram;
FIG. 11 shows an embodiment of the present invention with an electric field strength of Axial temperature gradient diagram of time series-parallel semi-crystalline PVDF polymer model;
FIG. 12 is a graph showing thermal conductivity of a series-parallel semicrystalline PVDF polymer as a function of applied electric field strength in accordance with an embodiment of the present invention.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
Example 1:
Taking polyvinylidene fluoride (PVDF) as an example, crystalline polymer of the beta type.
A modeling method and a thermal conductance optimization method of a polymer material serial-parallel semi-crystal model comprise the following steps:
step 1, establishing a beta-type crystalline polymer model of polyvinylidene fluoride (PVDF):
The lattice parameter of the unit cell is The space group is Cm2m, one unit cell contains two PVDF monomers (-CH 2-CF 2-), 4 PVDF monomers respectively contain C, H, F atoms as shown in figure 2 (a), then 4, 5 and 50 PVDF monomers are respectively expanded in the X, Y, Z direction to obtain a crystalline polymer model, the periodicity is removed, and the end C atoms of each main chain are added with hydrogen atoms to obtain a pure crystalline polymer model as shown in figure 2 (b);
step 2, selecting partial atoms in the central part as a permanent crystalline region according to the crystalline mass fraction, and then completely breaking bonds between the permanent crystalline region and end atoms of the temporary crystalline region, wherein 12 molecular chains in the central part are selected as the permanent crystalline region, and each molecular chain contains 26 PVDF monomers;
Step 3, designating the main chain atom at the end of the molecular chain of the permanent crystalline region as R1, designating the main chain atom at the end of the molecular chain of the temporary crystalline region as R2, and then connecting all the R1 and R2 atoms according to the simulation requirement to form a bridge-like link to obtain a model I, as shown in figure 3;
Step 4, using open source software Lammps as simulation software, and performing molecular dynamics simulation on the model I according to the following substeps:
(1) If the model I has periodicity in the initial stage, in order to avoid the disorder of key distribution caused by directly setting a vacuum layer, the model I can display the unfolding coordinates of each atom by means of the 'Unwrap trajectories' function in the visualization software ovito and then output a model file as Lammps again, then a box is simulated according to the size of the polymer after the model I is predicted and the corresponding size of the simulated box is adjusted, so that the model atoms are all positioned in the box to obtain a model II;
(2) Rendering color according to molecular chain sequence number by ovito software visualization model, observing whether the division of polymer molecular chain is correct or not, and correcting the molecular chain with wrong division to accurately extract the molecular sequence number of permanent crystal region or determine the molecular sequence number at the later stage, and further determining the atomic sequence number by judging z coordinate, wherein the initial molecular sequence number is arranged incorrectly in this example, as shown in fig. 4 (a), wherein the color allocation of the same molecular chain is inconsistent, so that the correct model is obtained after correction by the relevant code, as shown in fig. 4 (b);
(3) The center cross-section of fig. 4 (b) is depicted as shown in fig. 4 (c). It can be seen that the 'permanent crystalline region' is distributed in the middle region of the molecular chain in the central blue portion, indicated by the black dashed box in the figure. However, in the model, because part of atoms of the permanent crystalline region and the temporary crystalline region are located in the same molecular chain, the grouping of the permanent crystalline region cannot be directly performed through the molecular chain serial numbers (in the example, the molecular serial numbers of the atoms of the crystalline region are 11-14, 19-22 and 27-30), so that all the atoms on the molecular chain where the permanent crystalline region is located are firstly extracted, and then the atomic serial numbers of the permanent crystalline region are judged and recorded according to the coordinate values (37.5 < Z < 90.19) of the atoms in the Z direction;
(4) The interaction between atoms in the model II is described by adopting PCFF potential functions, the atomic type is set to be full, the simulation unit is set to be real, the neighbor list is set to be 2.0bin, the time step is set to be 0.5fs, the pressure is set to be 0atm, then the simulation temperature is set to be 800K, and the numerical value is obtained by directly carrying out heating melting simulation on the model shown in the figure 2 by utilizing Lammps;
(5) The potential of "pair_style" in PCFF force field is "lj/class2/coul/long", wherein 'long' represents that long-range coulomb interaction is considered, so that "kspace _ STYLE PPPM 1.0.0 e-6" needs to be set, but in order to avoid error reporting beyond coulomb interaction, only the spatial distribution of atoms is considered for model II initially, namely 'long' is changed into 'cut', and setting of "kspace _ STYLE PPPM 1.0e-6" is cancelled;
(6) After X, Y, Z three-direction boundary conditions are set as non-periodic boundary (f) conditions, in order to prevent simulation errors caused by movement of polymer atoms out of a simulation box in the process of local melting of a model II, reflecting walls are arranged on each surface of the simulation box, and then atoms in a permanent crystalline region are divided into the same crystalline group according to the atomic sequence number in the step (3);
(7) Fixing the permanent crystalline region by using a 'velocity CRYSTAL SET 000,fix crystal setforce 00 0' command, performing local melting simulation on the model II under a regular ensemble (NVT), obtaining a model III after relaxation for 1ns, as shown in fig. 5 (a), and drawing a cross-section, as shown in fig. 5 (b), wherein the permanent crystalline region in the model still maintains a crystalline conformation, and the temporary crystalline region is converted into an amorphous state;
(8) After resetting the long Cheng Kulun force interaction in the potential function, changing X, Y, Z three-direction boundary condition setting to periodic boundary (p) condition, canceling the reflecting wall set in the substep (6) of the step (4), canceling the fixed setting of the substep (7) 'permanent crystalline region' of the step (4), setting the simulated temperature at 300K, and observing fig. 5 (a) to find that no vacuum layer exists in the X and Y directions and a larger vacuum layer exists in the Z direction, in order to avoid model error when considering the long Cheng Kulun force, manually adjusting the vacuum layer size to a proper position, as shown in fig. 5 (c);
(9) And (3) relaxing the model III for 1ns under isothermal and isobaric ensemble (NPT) to obtain a model IV, wherein X, Y, Z directions conform to a semi-crystalline polymer model with a serial form, and the model is called a serial-parallel semi-crystalline polymer model. When the time reaches 1ns, the total energy of the system reaches a dynamic stable state, as shown in fig. 6, further proving the rationality of the obtained model, and if other molecular dynamics simulation software is needed to perform subsequent simulation, the data file can be converted into xyz file through ovito or converted into cif file through atomsk software, and then the mutual conversion among different types of model files is performed through MATERIALS STUDIO or VMD and other visual software.
Step 5, exploring the change of the morphology of the model IV after applying an equal-intensity electric field (ex=ey) in the X and Y directions:
The simulated temperature was first set above the amorphous polymer melting temperature and below the crystalline polymer melting point, and then the application in the X and Y directions, respectively, was investigated After 2ns of the equipotential field (E x＝Ey), the morphology of the series-parallel semi-crystalline polymer changes. As shown in fig. 7, which shows the model morphology change after the application of the electric field, the PVDF serial-parallel semicrystalline polymer will shrink in the X and Y directions and stretch in the Z direction after the application of the equal-strength electric field to the model. The electric field is removed after the electric field with different intensity is applied and the electric deformation is caused by 2ns, the sectional view of the model is shown in figure 8, and the 'permanent crystalline region' still keeps a better stable structure at the moment, then the temperature is reduced to 300K at room temperature, and the relaxation is respectively carried out for 2ns under NPT, NVT, NVE ensembles, so as to obtain the dynamic stable model at room temperature. And then carrying out heat transfer analysis by using an unbalanced molecular dynamics method, dividing the model into multiple layers along the heat transfer direction (Z direction), wherein the thickness of each layer is approximatelyAnd then, respectively controlling the temperature of the heat source and the heat sink by utilizing a Langevin method to ensure that the system generates heat flow until the heat flow basically keeps stable growth, counting a heat flow time change curve, as shown in figure 10, finally counting the temperature of each layer, and drawing a temperature change curve along the heat transfer direction along with the position of each layer, as shown in figure 11.
Step 6, calculating the influence of the electric field strength on the heat conduction performance of the PVDF serial-parallel semi-crystalline polymer:
The temperature gradient value and the time change rate of the heat flow are obtained by respectively carrying out linear fitting on the change curve of the temperature along with each layer position and the change curve of the heat flow along with time through python software, then the cross section size of the model is extracted, the heat conductivity coefficient of the material is calculated according to the Fourier law, and the influence of the change of the electric field strength on the heat conductivity of the polymer material is obtained, as shown in figure 12;
The foregoing is merely one of the embodiments of the present invention, and a person skilled in the art may make various modifications and follow the present invention without departing from the spirit and technical flow of the invention, so that simple modifications and equivalent changes of the invention fall within the scope of the claims of the present invention, and still fall within the technical scope of the invention.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims (9)

1.一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，包括以下步骤：1. A method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material, characterized by comprising the following steps: 步骤1：首先根据所需聚合物的种类建立相应尺寸的全晶态聚合物模型；Step 1: First, establish a fully crystalline polymer model of corresponding size according to the type of polymer required; 步骤2：按模拟需求选定中心部分的晶态区作为‘永久晶态区’，其他区域作为‘暂时晶态区’，并将‘永久晶态区’与‘暂时晶态区’间的原子间共价键进行断键；Step 2: According to the simulation requirements, the central crystalline region is selected as the ‘permanent crystalline region’ and the rest of the region is selected as the ‘temporary crystalline region’. The covalent bonds between the atoms in the ‘permanent crystalline region’ and the ‘temporary crystalline region’ are then broken. 步骤3：将‘永久晶态区’分子链端部主链原子命名为R1，将‘暂时晶态区’的分子链端部主链原子命名为R2，然后根据模拟需求将R1与R2原子随机形成共价键，获得具有不同链间耦合的模型I；Step 3: Name the main chain atom at the end of the molecular chain in the ‘permanent crystalline region’ R1, and the main chain atom at the end of the molecular chain in the ‘temporary crystalline region’ R2. Then, randomly form covalent bonds between R1 and R2 atoms according to simulation requirements to obtain Model I with different interchain couplings. 步骤4：用开源软件Lammps作为模拟软件，对模型Ⅰ进行分子动力学模拟，得到X、Y、Z三个方向均符合串联形态的半晶聚合物模型，称为串并联半晶聚合物模型IV，具体步骤为：Step 4: Use the open source software Lammps as the simulation software to perform molecular dynamics simulation on Model I, and obtain a semi-crystalline polymer model that conforms to the series morphology in the X, Y, and Z directions, called the series-parallel semi-crystalline polymer model IV. The specific steps are as follows: （1）根据模型Ⅰ预测变形后的聚合物大小模拟盒子并设置相应尺寸，且使模型原子全部位于盒子内部，得到模型II；(1) Based on the predicted size of the deformed polymer according to Model I, a simulation box is created and the corresponding size is set so that all the model atoms are located inside the box, thus obtaining Model II; （2）通过ovito软件可视化模型，将模型II按分子链序号进行渲染颜色，然后观察聚合物分子链的划分正确与否，并对划分错误的分子链进行修正,以在后期能正确提取永久晶态区的分子序号或确定分子序号后进一步通过判定z坐标确定原子序号；(2) Visualize the model using ovito software, render model II according to the molecular chain number, and then observe whether the division of the polymer molecular chain is correct or not, and correct the molecular chain that is incorrectly divided, so that the molecular number of the permanent crystalline region can be correctly extracted in the later stage, or the atomic number can be further determined by determining the z coordinate after the molecular number is determined; （3）记录‘永久晶态区’与‘暂时晶态区’的分子链之间不存在链间耦合的‘永久晶态区’的分子链序号；通过坐标位置进一步确定‘永久晶态区’与‘暂时晶态区’的分子链间存在链间耦合的‘永久晶态区’中的原子序号；(3) Record the molecular chain number of the ‘permanent crystalline region’ where there is no interchain coupling between the molecular chains of the ‘permanent crystalline region’ and the ‘temporary crystalline region’; further determine the atomic number of the ‘permanent crystalline region’ where there is interchain coupling between the molecular chains of the ‘permanent crystalline region’ and the ‘temporary crystalline region’ by coordinate position; （4）设置描述模型II中各原子之间相互作用的势函数，设置初始仿真条件和参数，其中设置的温度须超过晶态聚合物的融点；(4) Set the potential function that describes the interaction between atoms in Model II, set the initial simulation conditions and parameters, and the temperature must be higher than the melting point of the crystalline polymer; （5）对于所述的势函数，如考虑了长程库仑力相互作用，为避免获得初始串并联半晶聚合物模型时出错，先取消长程库仑力相互作用的设置，初始时只对模型II考虑分子链的空间位置分布；(5) For the potential function, if the long-range Coulomb force interaction is considered, in order to avoid errors when obtaining the initial series-parallel semi-crystalline polymer model, the setting of the long-range Coulomb force interaction is first canceled, and initially only the spatial position distribution of the molecular chain is considered for model II; （6）将X、Y、Z三方向的边界条件设置为非周期性边界f条件后，为防止模型II局部融化过程中聚合物原子运动到模拟盒子外导致模拟出错，在模拟盒子的各个面设置反射墙；根据步骤4的子步骤（3）中的原子序号将‘永久晶态区’内的原子划分为同一个晶态组，并将晶态组原子受力及速度均设置为0，形成可固定晶态区；(6) After setting the boundary conditions in the X, Y, and Z directions to non-periodic boundary f conditions, in order to prevent the polymer atoms from moving outside the simulation box during the local melting of Model II and causing simulation errors, reflection walls are set on each side of the simulation box; according to the atomic number in sub-step (3) of step 4, the atoms in the ‘permanent crystalline region’ are divided into the same crystalline group, and the force and velocity of the atoms in the crystalline group are set to 0, forming a fixed crystalline region; （7）采用正则系综NVT将模型II进行局部融化模拟，在高温熔化‘暂时晶态区’时，通过模拟命令固定‘永久晶态区’，经过1-2 ns后得到模型III，此时‘永久晶态区’仍保持晶态构象，而‘暂时晶态区’已转变为无定型态；(7) Model II was locally melted using the canonical ensemble NVT. When the ‘temporary crystalline region’ was melted at high temperature, the ‘permanent crystalline region’ was fixed by simulation commands. After 1-2 ns, Model III was obtained. At this time, the ‘permanent crystalline region’ still maintained the crystalline conformation, while the ‘temporary crystalline region’ had transformed into an amorphous state. （8）将模型III作为模型文件，并在势函数中设置长程库仑力相互作用后，将X、Y、Z三方向的边界条件设置改为周期性边界p条件，取消步骤4的子步骤（6）中设置的反射墙，取消步骤4的子步骤（7）中的固定‘永久晶态区’的设置，将模拟温度设置在晶态聚合物的熔点以下，避免后续晶态区发生结构破坏；(8) Use Model III as the model file and set the long-range Coulomb force interaction in the potential function. Then, change the boundary conditions in the X, Y, and Z directions to periodic boundary p conditions. Cancel the reflection wall set in sub-step (6) of step 4. Cancel the fixed ‘permanent crystalline zone’ setting in sub-step (7) of step 4. Set the simulation temperature below the melting point of the crystalline polymer to avoid structural damage in the subsequent crystalline zone. （9）将模型III在等温等压系综NPT下进行弛豫，经过1-2 ns后，即得到X、Y、Z三个方向均符合串联形态的半晶聚合物模型，称为串并联半晶聚合物模型IV；(9) Model III is relaxed under the isothermal and isobaric NPT ensemble. After 1-2 ns, a semi-crystalline polymer model with a series morphology in the X, Y, and Z directions is obtained, which is called the series-parallel semi-crystalline polymer model IV. 步骤5：将模型IV作为初始模型，探究在X与Y方向施加等强电场对串并联半晶聚合物形态的影响，并利用非平衡态分子动力学方法NEMD进行传热分析，得到温度随每层位置的变化曲线与热流随时间的变化曲线；Step 5: Using Model IV as the initial model, we investigated the effect of applying equal-strength electric fields in the X and Y directions on the morphology of the series-parallel semicrystalline polymers. We also used the nonequilibrium molecular dynamics (NEMD) method to perform heat transfer analysis, obtaining curves of temperature variation with position in each layer and heat flux variation with time. 步骤6：通过python软件分别对温度随每层位置的变化曲线与热流随时间的变化曲线进行线性拟合，得到温度梯度值与热流随时间变化率，根据傅里叶定律计算材料的导热系数，得出电场强度的变化对聚合物材料导热性能的影响。Step 6: Use Python software to perform linear fitting on the temperature change curve of each layer position and the heat flow change curve over time to obtain the temperature gradient value and the rate of change of heat flow over time. Calculate the thermal conductivity of the material according to Fourier's law, and obtain the effect of changes in electric field intensity on the thermal conductivity of polymer materials. 2.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，步骤2中的‘永久晶态区’被‘暂时晶态区’全部包围，以确保在后续模拟局部熔化的过程中晶态区链间方向或沿链方向的端部存在无定型聚合物链。2. The method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material as claimed in claim 1, wherein the permanent crystalline region in step 2 is completely surrounded by the temporary crystalline region to ensure that amorphous polymer chains are present at the ends of the crystalline region in the interchain direction or along the chain direction during the subsequent simulation of local melting. 3.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，步骤3中获得具有不同链间耦合的模型I，是根据模拟需求设置模型I中的链间耦合，具体是根据端部原子成键的键长进行判定，对距离超过键长的不进行连接，以防止模型I结构不合理。3. A modeling and thermal conductivity optimization method for a series-parallel semi-crystalline model of a polymer material according to claim 1, characterized in that in step 3, a model I with different interchain couplings is obtained, and the interchain coupling in the model I is set according to the simulation requirements, specifically, the interchain coupling is determined according to the bond length of the end atoms, and the distance exceeding the bond length is not connected to prevent the unreasonable structure of the model I. 4.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，所述步骤（1）中，对模型盒子增加对称分布的真空层，以防止某一侧有较多的无定型链集中。4. The method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material according to claim 1, wherein in step (1), symmetrically distributed vacuum layers are added to the model box to prevent a large number of amorphous chains from concentrating on one side. 5.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，所述步骤（2）中，观察聚合物分子链具体为：通过文本方式打开模型II文件，观察“Atoms”下的数据的第二列，以符合模型的分子总数为标准来判断分子序号划分的正确与否。5. The method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material according to claim 1, wherein in step (2), observing the polymer molecular chain is specifically performed by opening the Model II file in text format, observing the second column of data under "Atoms", and judging whether the molecular number division is correct based on the total number of molecules that meet the model. 6.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，所述步骤（4）中，初始仿真条件和参数包括模型尺寸、原子类型、单位制、边界条件、邻居列表半径、时间步长、压强、温度；所述晶态聚合物的熔点根据文献确定或利用Lammps模拟聚合物升温过程确定。6. The method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material according to claim 1, wherein in step (4), the initial simulation conditions and parameters include model size, atomic type, unit system, boundary conditions, neighbor list radius, time step, pressure, and temperature; and the melting point of the crystalline polymer is determined according to literature or by using Lammps to simulate the polymer heating process. 7.如权利要求1所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，所述步骤（8）还包括：若聚合物链在模拟盒子中均有分布则直接进行下一步模拟；若模拟盒子中聚合物链团簇在‘永久晶态区’周围，有较大的真空层，则在模型文件中缩小真空层范围，防止在等温等压系综NPT下弛豫时因超出长程库仑力相互作用范围报错。7. The modeling and thermal conductivity optimization method of a series-parallel semi-crystal model of a polymer material as described in claim 1 is characterized in that the step (8) also includes: if the polymer chains are distributed in the simulation box, then the next simulation is directly carried out; if the polymer chain clusters in the simulation box are around the "permanent crystalline region" and there is a large vacuum layer, then the vacuum layer range is reduced in the model file to prevent an error from being reported due to exceeding the long-range Coulomb force interaction range during relaxation under the isothermal and isobaric ensemble NPT. 8.如权利要求1-7任一项所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，步骤5中，在探究X与Y方向同时施加等强电场对串并联半晶聚合物形态的影响时，施加电场强度不超过聚合物的击穿电场强度值；模拟温度设置在无定型态聚合物熔化温度之上且低于晶态聚合物熔点；施加完电场后，将模型降温到室温后，再测定施加不同强度的电场对模型导热性能的影响。8. A method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material according to any one of claims 1 to 7, characterized in that in step 5, when investigating the effect of simultaneously applying equal-strength electric fields in the X and Y directions on the morphology of the series-parallel semi-crystalline polymer, the applied electric field strength does not exceed the breakdown electric field strength value of the polymer; the simulation temperature is set above the melting temperature of the amorphous polymer and below the melting point of the crystalline polymer; after applying the electric field, the model is cooled to room temperature, and then the effect of applying electric fields of different intensities on the thermal conductivity of the model is measured. 9.如权利要求8所述的一种聚合物材料串并联半晶模型的建模与热导优化方法，其特征在于，步骤5中，非平衡态分子动力学方法具体为：将模型沿热传导方向平均划分为 N层，统计并输出各层在稳定热流下的温度梯度，利用傅里叶定律计算热导率，其中 N 取决于模型长度且N≥8。9. The method for modeling and optimizing thermal conductivity of a series-parallel semi-crystalline model of a polymer material according to claim 8, wherein in step 5, the non-equilibrium molecular dynamics method specifically comprises: dividing the model into N layers evenly along the heat conduction direction, calculating and outputting the temperature gradient of each layer under a stable heat flow, and calculating the thermal conductivity using Fourier's law, where N depends on the model length and N ≥ 8.
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