A method for constructing a closed cell molecular model of foaming polymer

Abstract

The invention discloses a method for constructing a closed cell molecular model of a foaming polymer, and relates to the technical field of molecular simulation methods. The method comprises: constructing an initial molecular model of a polymer, adding an OPLSAA force field to the initial molecular model of the polymer; performing energy minimization processing on the model; performing dynamic relaxation on the model; introducing cells into the model to generate a closed cell model of a polymer with a target density; releasing local stresses generated by cell constraints; after the density and conformation of the closed cell model of the polymer are stable, removing internal and external cell constraints to obtain a closed cell molecular model of a foaming polymer with a stable configuration. The method realizes the construction of a closed cell molecular model of a foaming polymer, is helpful for the development of molecular simulation work of foaming polymers, clarifies the microscopic mechanism of deformation and mechanical properties of foaming polymers, and promotes the improvement of the performance of foaming polymer materials.

Description

Technical Field

[0001] The invention relates to the technical field of molecular simulation methods, and in particular to a method for constructing a closed-cell molecular model of a foaming polymer. Background Art

[0002] Foamed polymers have been widely used in practical engineering, especially in trenchless non-destructive repair, because of their good impermeability, durability, and environmental protection. Mechanical properties are the main factors that determine their repair effect. The main factors that affect the mechanical properties of foamed polymers are density, strain rate, temperature, etc. Therefore, extensive experiments and finite element simulation studies have been carried out at home and abroad to reveal the general laws of the influence of the above main factors on the macroscopic mechanical properties of foamed polymer materials, and have achieved certain beneficial understandings. The macroscopic performance of the mechanical properties of materials is determined by the microscopic molecular motion mechanism. It is difficult for existing macroscopic experiments to explain the deformation and destruction mechanism of foamed polymers from the molecular scale. In response to the above problems, some scholars at home and abroad used molecular dynamics simulation methods to study the microscopic mechanical properties of polymer elastomers and the motion mechanism of molecular chains in the system when they are deformed by force, and explained the reasons for the changes in the macroscopic mechanical properties of polymers from the molecular scale. Although relevant research work has been reported one after another, there is still a lack of molecular dynamics simulation research on foamed polymer materials. When foamed polymers are deformed by force, the internal molecular motion mechanism and how it is different from polymer elastomers are still unclear.

[0003] Molecular dynamics simulation is a numerical simulation technology that simulates the motion of molecules. By solving the Newtonian equations of motion of the atoms in the system, we can obtain information such as the positions of the atoms in the system at different times, changes in the system structure, the energy of the system and atoms, and the thermodynamic properties of the system. It can explain the mechanical properties of materials at the molecular scale, which makes up for the shortcomings of experiments. With the rapid development of computer computing power and calculation algorithms in recent years, molecular dynamics simulation has been widely used in polymer research. At present, there are no reports on the research methods for constructing closed cell molecular models of foamed polymers with different densities. Summary of the invention

[0004] Based on this, the present invention provides a method for constructing a closed-cell molecular model of a foaming polymer, so as to realize the construction of a closed-cell molecular model of a foaming polymer.

[0005] A method for constructing a closed cell molecular model of a foamed polymer of the present invention comprises the following steps:

[0006] Step 1: Use the Amorphous Cell module in Materials Studio software to build an initial polymer molecular model, and use Python programming to add the OPLSAA force field to the initial polymer molecular model;

[0007] Step 2: Use Lammps software to perform energy minimization on the initial polymer molecular model after adding the force field;

[0008] Step 3: Use Lammps software to perform dynamic relaxation on the initial molecular model of the polymer after energy minimization;

[0009] Step 4: Introduce cells into the initial polymer molecular model after relaxation to generate a polymer closed cell model of target density;

[0010] Step 5: Release the local stress generated by cell constraints in the polymer closed cell model;

[0011] Step 6: After the density and conformation of the polymer closed cell model are stabilized, remove the internal and external cell constraints, perform NPT relaxation on the polymer closed cell model at 600K, set the relaxation time to 100Ps, and set the pressure to 1Pa; cool the relaxed polymer closed cell model to 300K, and continue to perform NPT relaxation on the polymer closed cell model at 300K, set the relaxation time to 100Ps, and set the pressure to 1Pa, to obtain a foaming polymer closed cell molecular model with a stable configuration.

[0012] Optionally, the step of adding the OPLSAA force field to the initial polymer molecular model by using a Python program includes:

[0013] The OPLSAA force field parameters corresponding to the initial polymer molecular model are obtained in LigParGen, and then a Python script is written to modify the atomic type and topological type of the initial polymer molecular model according to the atomic type and topological type contained in the OPLSAA force field parameters, so that the atomic type and topological type of the initial polymer molecular model are consistent with the atomic type and topological type contained in the OPLSAA force field parameters.

[0014] Optionally, the energy minimization process of the initial polymer molecular model after adding the force field by using Lammps software includes:

[0015] In Lammps software, use the min_style command, select the Polak-Ribiere version of the conjugate gradient algorithm, set the maximum number of iterations to 5000, and set the time step to 0.5 fs.

[0016] Optionally, introducing cells into the initial molecular model of the polymer after relaxation to generate a polymer closed cell model of target density includes:

[0017] Introducing a spherical cell into the initial molecular model of the polymer after relaxation, which is recorded as an internal cell. The center of the internal cell coincides with the center of the initial molecular model of the polymer, and the pore size of the internal cell gradually increases from zero.

[0018] A spherical cell is introduced outside the polymer initial molecular model after the internal cell is introduced, which is recorded as an external cell. The center of the external cell coincides with the center of the polymer initial molecular model. The minimum initial pore size of the external cell is calculated based on the standard of completely enveloping all atoms of the polymer initial molecular model. The pore size of the external cell is continuously reduced.

[0019] The initial polymer molecular model with internal and external pores introduced is recorded as a polymer closed cell model, and the change rate of the internal and external pores of the polymer closed cell model is adjusted until the polymer closed cell model reaches the target density.

[0020] Optionally, introducing cells into the initial molecular model of the polymer after relaxation to generate a polymer closed cell model of target density includes:

[0021] In Lammps software, the fix indent command is used to set the force constant to 10. The increase rate of the internal pores and the decrease rate of the external pores are set according to the size of the polymer closed pore model and the target density. The minimum initial pore size of the external pores is calculated by the following formula:

[0022]

[0023] Among them, r 外 is the minimum initial pore size of the external pores, and L is the side length of the initial molecular model of the polymer after relaxation.

[0024] Optionally, the step of performing dynamic relaxation on the initial polymer molecular model after energy minimization using Lammps software includes:

[0025] The initial polymer molecular model after energy minimization was subjected to 100 Ps NVT dynamic relaxation to fully relax each independent polymer chain in the initial polymer molecular model. During the relaxation process, the force field was set to OPLSAA force field, the temperature was controlled by Nose heat bath method, the pressure was controlled by Berendsen constant pressure method, the van der Waals force was solved by LJ interaction, and the electrostatic interaction was solved by PPPM method.

[0026] Perform NPT molecular dynamics simulation on the initial polymer molecular model, and continue to relax the initial polymer molecular model under the conditions of 800Pa pressure and 600K temperature, setting the relaxation time to 1000ps and the time step to 0.5fs;

[0027] The temperature of the initial polymer molecular model is controlled to be constant, and the pressure is reduced to 1 Pa. After the pressure reduction is completed, the pressure and temperature are controlled to be constant. Under the conditions of 1 Pa pressure and 600 K temperature, the initial polymer molecular model continues to be relaxed, and the relaxation time is set to 100 ps.

[0028] Optionally, the releasing of local stress generated by cell constraints in a polymer closed cell model includes:

[0029] After the polymer closed cell model reaches the target density, the internal cell diameter and the external cell diameter are recorded as r 内end and r 外end ; Maintain the internal cell diameter r 内end The pore size of the external pores increases from the initial value r 外 Gradually decrease to r 外end , repeated cycles until the external cell diameter increases from the initial value r 外 Reduce to r 外end During the process, the density and conformation of the polymer closed cell model do not change.

[0030] Beneficial effects of the present invention:

[0031] The method for constructing a closed-cell molecular model of a foamed polymer of the present invention makes up for the shortcomings of existing polymer molecular models and is helpful for the development of molecular simulation of foamed polymers. The model can be used to further clarify the microscopic mechanism of macroscopic deformation and macroscopic mechanical properties of foamed polymers, promote the improvement of the performance of foamed polymer materials, and give full play to the engineering benefits of foamed polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0033] Figure 1 It is a flow chart of a method for constructing a closed cell molecular model of a foaming polymer provided by the present invention;

[0034] Figure 2 It is a chemical structural formula diagram of a long-chain polyurethane provided by the present invention;

[0035] Figure 3 It is a polyurethane molecular model diagram after dynamic relaxation provided by the present invention;

[0036] Figure 4It is a diagram of the foaming process of the polymer closed cell model provided by the present invention;

[0037] Figure 5 The 0.35 g / cm 3 Cross-section of a closed-cell molecular model of a foamed polymer. DETAILED DESCRIPTION

[0038] In the following description, for the purpose of explanation rather than limitation, specific details such as specific system structures and technologies are provided to facilitate a thorough understanding of the embodiments of the present invention. In order to illustrate the technical solution of the present invention, a specific embodiment is provided below for illustration.

[0039] See also Figure 1 , is a flow chart of a method for constructing a closed cell molecular model of a foaming polymer provided in this embodiment, and the method may include the following steps:

[0040] Step 1: Use the Amorphous Cell module in Materials Studio software to build an initial polymer molecular model, and use Python programming to add the OPLSAA force field to the initial polymer molecular model.

[0041] In this embodiment, the polymer selected for the initial molecular model of the polymer is a non-aqueous reaction foaming polyurethane, and the main synthetic materials of the non-aqueous reaction foaming polyurethane are polyphenylmethane polyisocyanate (MDI) and sucrose polyether polyol, with a structural formula as follows: Figure 2 As shown, the Amorphous Cell module in Materials Studio software is used to build an initial polymer molecular model, and Python programming is used to add the OPLSAA force field to the initial polymer molecular model.

[0042] The specific implementation method of adding OPLSAA force field to the initial polymer molecular model is: obtain the OPLSAA force field parameters corresponding to the initial polymer molecular model in LigParGen, and then write a Python script to modify the atomic type and topological type of the initial polymer molecular model according to the atomic type and topological type contained in the OPLSAA force field parameters, so that the atomic type and topological type of the initial polymer molecular model are consistent with the atomic type and topological type contained in the OPLSAA force field parameters.

[0043] Step 2: Use Lammps software to perform energy minimization on the initial polymer molecular model after adding the force field.

[0044] In this embodiment, the initial polymer molecular model is optimized by performing energy minimization processing on the initial polymer molecular model after adding the force field. The specific implementation method of the energy minimization processing is: using the min_style command in Lammps software, selecting the Polak-Ribiere version of the conjugate gradient (cg) algorithm, setting the maximum number of iterations to 5000 steps, and setting the time step to 0.5 fs.

[0045] Step 3: Use Lammps software to perform dynamic relaxation on the initial polymer molecular model after energy minimization.

[0046] In this embodiment, the specific method of using Lammps software to perform dynamic relaxation on the initial molecular model of the polymer after energy minimization is as follows:

[0047] Step 301, perform 100Ps NVT dynamic relaxation on the initial polymer molecular model after energy minimization, so that each independent polymer chain in the initial polymer molecular model can be fully relaxed; during the relaxation process, set the force field to be the OPLSAA force field, use the Nose heat bath method to control the temperature, use the Berendsen constant pressure method to control the pressure, use the LJ interaction to solve the van der Waals force, and use the PPPM method to solve the electrostatic interaction.

[0048] Step 302, perform NPT molecular dynamics simulation on the initial polymer molecular model, continue to relax the initial polymer molecular model under the conditions of 800Pa pressure and 600K temperature, set the relaxation time to 1000ps, and set the time step to 0.5fs.

[0049] Step 303, control the temperature of the initial polymer molecular model to remain unchanged, reduce the pressure to 1Pa, and after the pressure reduction is completed, control the pressure and temperature to remain unchanged, and continue to relax the initial polymer molecular model under the conditions of 1Pa pressure and 600K temperature, and set the relaxation time to 100ps.

[0050] Step 4: Introduce cells into the initial polymer molecular model after relaxation to generate a polymer closed cell model of target density.

[0051] like Figure 4 The figure shows the foaming process of the polymer closed cell model. A spherical cell is introduced into the initial molecular model of the polymer after relaxation, which is recorded as the internal cell. The center of the internal cell coincides with the center of the initial molecular model of the polymer, and the pore size of the internal cell gradually increases from zero.

[0052] In order to reflect the restraining effect of other pores and the surrounding polymer matrix on the expansion of the pores during the expansion process, a spherical pore is introduced outside the initial polymer molecular model after the introduction of the internal pores, which is recorded as the external pore. The center of the external pore coincides with the center of the initial polymer molecular model. The minimum initial pore size of the external pore is calculated based on the standard of completely enveloping all the atoms of the initial polymer molecular model, and the pore size of the external pore keeps decreasing.

[0053] The initial polymer molecular model with internal and external pores introduced is recorded as a polymer closed cell model, and the change rate of the internal and external pores of the polymer closed cell model is adjusted until the polymer closed cell model reaches the target density.

[0054] In this embodiment, the method of introducing internal and external cells is: using the fix indent command in Lammps software, setting the force constant to 10, the increase rate of the internal cells and the decrease rate of the external cells are set according to the size of the polymer closed cell model and the target density, and the minimum initial pore size of the external cells is calculated by the following formula (1):

[0055]

[0056] Among them, r 外 is the minimum initial pore size of the external pores, and L is the side length of the initial molecular model of the polymer after relaxation.

[0057] In order to obtain a 0.35 g / cm3 polymer closed cell model, the increasing rate of the inner cell diameter and the decreasing rate of the outer cell diameter were both set to 0.1 nm / ps.

[0058] Step 5: Release the local stress generated by cell constraints in the polymer closed cell model.

[0059] In this embodiment, the method for releasing the local stress generated by the internal and external cell constraints is: after the polymer closed cell model reaches the target density, the internal cell diameter and the external cell diameter are respectively recorded as r 内end and r 外end Then keep the internal cell diameter r 内end The pore size of the external pores increases from the initial value r 外 Then gradually decrease to r 外end , repeated cycles until the external cell diameter increases from the initial value r 外 Reduce to r 外end During the process, the density and conformation of the polymer closed cell model have no obvious changes, and the polymer closed cell model has reached a stable state.

[0060] Step 6: After the density and conformation of the polymer closed cell model are stabilized, remove the internal and external cell constraints, perform NPT relaxation on the polymer closed cell model at 600K, set the relaxation time to 100Ps, and set the pressure to 1Pa; cool the relaxed polymer closed cell model to 300K, and continue to perform NPT relaxation on the polymer closed cell model at 300K, set the relaxation time to 100Ps, and set the pressure to 1Pa, to obtain a foaming polymer closed cell molecular model with a stable configuration.

[0061] As an example, the cross-sectional view of the closed cell molecular model of the 0.35 g / cm3 foamed polymer obtained in this embodiment is as follows: Figure 5 shown.

[0062] The method for constructing a closed-cell molecular model of a foamed polymer in this embodiment makes up for the shortcomings of existing polymer molecular models and is helpful in carrying out molecular simulation work of foamed polymers. The model can be used to further clarify the microscopic mechanism of the macroscopic deformation and macroscopic mechanical properties of foamed polymers, promote the improvement of the performance of foamed polymer materials, and give full play to the engineering benefits of foamed polymers.

[0063] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for constructing a closed cell molecular model of a foaming polymer, characterized in that: include: Step 1: Use the Amorphous Cell module in Materials Studio software to build an initial polymer molecular model, and use Python programming to add the OPLSAA force field to the initial polymer molecular model; Step 2: Use Lammps software to perform energy minimization on the initial polymer molecular model after adding the force field; Step 3: Use Lammps software to perform dynamic relaxation on the initial molecular model of the polymer after energy minimization; Step 4: Introduce cells into the initial polymer molecular model after relaxation to generate a polymer closed cell model of target density; Step 5: Release the local stress generated by cell constraints in the polymer closed cell model; Step 6: After the density and conformation of the polymer closed cell model are stabilized, the internal and external cell constraints are removed, and the polymer closed cell model is subjected to NPT relaxation at a temperature of 600K, with the relaxation time set to 100Ps and the pressure set to 1Pa; the relaxed polymer closed cell model is cooled to 300K, and the polymer closed cell model is further subjected to NPT relaxation at a temperature of 300K, with the relaxation time set to 100Ps and the pressure set to 1Pa, to obtain a foaming polymer closed cell molecular model with a stable configuration; The local stress generated by cell constraints in the release polymer closed cell model includes: After the polymer closed cell model reaches the target density, the internal cell diameter and the external cell diameter are recorded as r 内end and r 外end ; Maintain the internal cell diameter r 内end The pore size of the external pores increases from the initial value r 外 Gradually decrease to r 外end , repeated cycles until the external cell diameter increases from the initial value r 外 Reduce to r 外end During the process, the density and conformation of the polymer closed cell model do not change.

2. The method for constructing a closed cell molecular model of a foaming polymer according to claim 1, characterized in that: The use of Python programming to add the OPLSAA force field to the initial polymer molecular model includes: The OPLSAA force field parameters corresponding to the initial polymer molecular model are obtained in LigParGen, and then a Python script is written to modify the atomic type and topological type of the initial polymer molecular model according to the atomic type and topological type contained in the OPLSAA force field parameters, so that the atomic type and topological type of the initial polymer molecular model are consistent with the atomic type and topological type contained in the OPLSAA force field parameters.

3. The method for constructing a closed cell molecular model of a foaming polymer according to claim 1, characterized in that: The energy minimization process of the initial polymer molecular model after adding the force field by using Lammps software includes: In Lammps software, use the min_style command, select the Polak-Ribiere version of the conjugate gradient algorithm, set the maximum number of iterations to 5000, and set the time step to 0.5 fs.

4. The method for constructing a closed cell molecular model of a foaming polymer according to claim 1, characterized in that: Introducing cells into the initial polymer molecular model after relaxation, generating a polymer closed cell model of target density includes: Introducing a spherical cell into the initial molecular model of the polymer after relaxation, which is recorded as an internal cell. The center of the internal cell coincides with the center of the initial molecular model of the polymer, and the pore size of the internal cell gradually increases from zero. A spherical cell is introduced outside the polymer initial molecular model after the internal cell is introduced, which is recorded as an external cell. The center of the external cell coincides with the center of the polymer initial molecular model. The minimum initial pore size of the external cell is calculated based on the standard of completely enveloping all atoms of the polymer initial molecular model. The pore size of the external cell is continuously reduced. The initial polymer molecular model with internal and external pores introduced is recorded as a polymer closed cell model, and the change rate of the internal and external pores of the polymer closed cell model is adjusted until the polymer closed cell model reaches the target density.

5. The method for constructing a closed cell molecular model of a foaming polymer according to claim 4, characterized in that: Introducing cells into the initial polymer molecular model after relaxation, generating a polymer closed cell model of target density includes: In Lammps software, the fix indent command is used to set the force constant to 10. The increase rate of the internal pores and the decrease rate of the external pores are set according to the size of the polymer closed pore model and the target density. The minimum initial pore size of the external pores is calculated by the following formula: Among them, r 外 is the minimum initial pore size of the external pores, and L is the side length of the initial molecular model of the polymer after relaxation.

6. The method for constructing a closed cell molecular model of a foaming polymer according to claim 1, characterized in that: The method of using Lammps software to perform dynamic relaxation on the initial molecular model of the polymer after energy minimization treatment includes: The initial polymer molecular model after energy minimization was subjected to 100 Ps NVT dynamic relaxation to fully relax each independent polymer chain in the initial polymer molecular model. During the relaxation process, the force field was set to OPLSAA force field, the temperature was controlled by Nose heat bath method, the pressure was controlled by Berendsen constant pressure method, the van der Waals force was solved by LJ interaction, and the electrostatic interaction was solved by PPPM method. Perform NPT molecular dynamics simulation on the initial polymer molecular model, and continue to relax the initial polymer molecular model under the conditions of 800Pa pressure and 600K temperature, setting the relaxation time to 1000ps and the time step to 0.5fs; The temperature of the initial polymer molecular model is controlled to be constant, and the pressure is reduced to 1 Pa. After the pressure reduction is completed, the pressure and temperature are controlled to be constant. Under the conditions of 1 Pa pressure and 600 K temperature, the initial polymer molecular model continues to be relaxed, and the relaxation time is set to 100 ps.

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