Polymerization simulation method of geopolymer gel based on reaction molecular dynamics

Abstract

According to the polymerization simulation method of the geopolymer gel based on the reaction molecular dynamics, the whole process simulation from Si and Al tetrahedron monomers to C (N)-A-S-H gel polymerization is realized, and the whole C (N)-A-S-H gel polymerization process can be simulated and tracked from the initial stage of Si and Al tetrahedrons. The innovative method enables researchers to comprehensively understand the formation mechanism of the geopolymer material, fills the blank of lack of research on the whole polymerization process in traditional simulation, and provides a scientific basis for subsequent optimization and application of the C (N)-A-S-H gel modified material. The influence of GO on the C (N)-A-S-H gel is combined with the polymerization process of the C (N)-A-S-H gel in molecular dynamics simulation for the first time, and the influence of GO in the polymerization process of the C (N)-A-S-H gel is reflected. Compared with other atom substitution method modeling, the GO / C (N)-A-S-H gel molecule model established through GO and monomer polymerization can better ascertain how the GO and the C (N)-A-S-H gel molecules are connected, and no longer depends on guess.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular dynamics simulation, and specifically relates to a polymerization simulation method of geopolymer gel based on reactive molecular dynamics. This method studies the polymerization process of C(N)-A-S-H gel in geopolymer through molecular dynamics simulation means. Background Art

[0002] Geopolymer concrete is an environmentally friendly building material made by reacting materials rich in silicon and aluminum, such as fly ash and slag, with alkaline activators. Its unique chemical reaction and cement replacement characteristics give it significant advantages in reducing carbon dioxide emissions and improving the durability of concrete. In recent years, geopolymer concrete has received extensive attention in the fields of construction, engineering, and environmental protection.

[0003] Geopolymer is an inorganic cementitious material formed by alkaline activation of mineral raw materials rich in aluminosilicate. Geopolymer alkali-activated cementitious materials are a type of aluminosilicate material with an amorphous to semi-crystalline molecular structure, composed of [SiO 4 4- and [AlO 4 5- tetrahedra cross-linked by shared oxygen atoms. Inside the geopolymer, C(N)-A-S-H gel is formed through a polymerization reaction. Due to its stable disordered silicon-aluminum oxide tetrahedral structure, the geopolymer has good mechanical properties, acid and alkali corrosion resistance, and high-temperature thermal stability. However, this disordered amorphous structure also increases the difficulty of its research. Existing experimental studies on C(N)-A-S-H gel at the atomic scale are not yet complete. To explore this problem, molecular dynamics simulation means are usually used for research. Existing molecular dynamics simulation studies to establish the C(N)-A-S-H gel molecular model are mostly achieved by the tobermorite model (or NAS glass model) atom replacement method or the oligomer polymerization method. The defect of the atom replacement method is that it skips the polymerization process of the geopolymer and cannot study the influence of the polymerization reaction. At the same time, the generated model structure tends to the original model and cannot reflect the disordered amorphous nature of the C(N)-A-S-H gel molecular model. The oligomer polymerization method determines the structure of the geopolymer after polymerization by the selected oligomer structure, and cannot reasonably explore the molecular chain type between [SiO 4 4- and [AlO 4 5- tetrahedra, and ignores the process of synthesizing oligomers from [SiO 4 4- and [AlO 4 5- tetrahedron monomers during the polymerization process. Summary of the Invention

[0004] ​​​​​​To overcome the problems existing in the above-mentioned existing molecular dynamics simulations, the object of the present invention is to provide a polymerization simulation method for geopolymer gels based on reactive molecular dynamics. This method is based on molecular dynamics simulations to construct monomers from [SiO 4 4- and [AlO 4 5- tetrahedrons and polymerize them into C(N)-A-S-H gels. Using molecular dynamics simulations, considering the force field, setting the polymerization process parameter conditions, and establishing a C(N)-A-S-H gel molecular model that meets the requirements, thus providing a scientific method for molecular dynamics simulation studies on the polymerization process of C(N)-A-S-H gels and the modification effect of externally added substances (such as graphene oxide (GO, Graphene oxidemodel)) on C(N)-A-S-H gels during the polymerization process. At the same time, a tensile simulation experiment for testing the mechanical properties of C(N)-A-S-H gels is also provided.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A polymerization simulation method for geopolymer gels based on reactive molecular dynamics, the method comprising the following steps:

[0007] (1) Construct monomers:

[0008] Use modeling software to establish [SiO 4 4- tetrahedrons and [AlO 4 5- tetrahedrons, and connect 4 hydrogen atoms to each tetrahedron. At the same time, add Na 4 5- ions near the [AlO + tetrahedron to generate two monomers, Si(OH) 4 and NaAl(OH) 4 . At the same time, use modeling software to establish a Ca(OH) 2 monomer, which serves as the calcium source for the C(N)-A-S-H gel molecular model;

[0009] (2) Establish a precursor model

[0010] Generate a box in the modeling software. According to the requirements of a density of 1.80 - 2.20 g / cm 3 , an Si / Al ratio of 2 - 3, and a Ca atomic content not greater than the Si atomic content, randomly distribute and fill the box with the two monomers, Si(OH) 4 and NaAl(OH) 4 , and the Ca(OH) 2 monomer to form a precursor model; ​​​​​

[0011] (3) Simulate the polymerization process

[0012] Select the ReaxFF force field file applicable to Si, Al, O, and Ca elements, import the precursor model into LAMMPS, perform energy minimization, and then relax it by equilibrating for 100 ps in the NPT ensemble and NVT ensemble at a time step of 0.25 fs and 300 K respectively;

[0013] Set the maximum temperature for simulating polymerization, the time for the water removal process, and the initial temperature of the water removal process. In the NVT ensemble at a time step of 0.1 fs, heat up from 300 K to the maximum temperature at a rate of 10 K / ps. When reaching the initial temperature of the water removal process, simultaneously execute the fix reaxff / species command to remove water molecules until the set time for the water removal process is reached, then stop removing water molecules;

[0014] Then cool down from the maximum temperature to 300 K at a rate of 10 K / ps in the NVT ensemble to simulate the polymerization process. The monomers will undergo the polymerization reaction shown in formula (1) (the hydrogen ions do not represent an acidic environment) to generate the C(N)-A-S-H gel molecular model;

[0015]

[0016] Finally, equilibrate for 300 ps in the NPT ensemble and NVT ensemble at a time step of 0.1 fs and 300 K respectively to obtain a stable C(N)-A-S-H gel molecular model;

[0017] (4) Structure inspection

[0018] Statistically analyze the average bond length of Si-O b the average bond length of Al-O b the average bond length of Si-O b -Si bond angle, the average bond length of Al-O b -Al bond angle, the average bond length of Si-O b -Al bond angle in the stable C(N)-A-S-H gel molecular model. If the statistical values meet the standards, it proves that the structure is reasonable; if the structure is unreasonable, adjust the force field file or change the maximum temperature, where O b is the bridging oxygen atom;

[0019] The said standards are as follows: the average bond length of Si-O in the C(N)-A-S-H gel molecular model b is in the range of the average bond length of Al-O b is in the range of the Si-O b -Si bond angle is 136°±5°, the Al-O b -Al bond angle is 152°±5°, and the Si-O bThe Al-O bond angles are concentrated in the range of 100° to 116°;

[0020] (5) Calculate the degree of polymerization

[0021] Set the degree of polymerization threshold, calculate the degree of polymerization for the C(N)-A-S-H gel molecular model with a reasonable structure. If the degree of polymerization is not less than the degree of polymerization threshold, the polymerization requirement is met, and the simulation result is obtained; if the degree of polymerization is less than the degree of polymerization threshold, the polymerization requirement is not met, and the type of force field file is changed or the time of the dehydration process and the initial temperature of the dehydration process are adjusted.

[0022] Furthermore, the monomer parameters are respectively:

[0023] Si(OH) 4 The bond length of the monomer is The bond angle is 109.5°; NaAl(OH) 4 The bond length of the monomer is The bond angle is 109.5°; Ca(OH) 2 The bond length of the monomer is The bond angle is 180°.

[0024] Preferably, during the simulation of the polymerization process, the NPT ensemble and the NVT ensemble are relaxed in sequence.

[0025] Preferably, the highest temperature for the simulation of polymerization is 3000K, the time of the dehydration process is 10ps, and the initial temperature of the dehydration process is 1300K.

[0026] Furthermore, the degree of polymerization C of the C(N)-A-S-H gel molecule is determined according to formula (3),

[0027]

[0028] where f = 4, X is the Si / Al ratio, Q m and Q n are respectively the percentages of the number of Si atoms bridging m oxygen atoms and the number of Al atoms bridging n oxygen atoms.

[0029] Furthermore, the C(N)-A-S-H gel molecular model that meets the polymerization requirements can perform a tensile simulation. The process of the tensile simulation is as follows: It is carried out with a time step of 0.25fs. The C(N)-A-S-H gel molecular model is in the NPT ensemble at 300K, and both ends are fixed Tensile at a strain rate of 0.0001 / ps and output the stress-strain diagram; obtain the maximum stress and Young's modulus from the stress-strain diagram.

[0030] Furthermore, when studying the influence of graphene oxide GO or other externally doped substances on the polymerization process, when filling Si(OH)4 , NaAl(OH) 4 and Ca(OH) 2 Before adding the admixture and then filling, or randomly distributing and filling together with the monomer;

[0031] During the simulation of the polymerization process, the admixture is grouped before the start of the simulation, and the main skeleton part of the admixture is fixed after energy minimization, and then the polymerization simulation is carried out.

[0032] When studying the influence of GO incorporation on the polymerization process, GO will decompose at high temperature in the simulation and GO does not directly participate in the polymerization reaction. Therefore, GO is grouped before the start of the simulation, and the main carbon atom skeleton part of GO is fixed after energy minimization to prevent GO from thermal decomposition or the detachment of the functional groups of GO.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The method of the present invention realizes the full-process simulation of the polymerization from Si and Al tetrahedral monomers to C(N)-A-S-H gel, and can start from the initial stage of Si and Al tetrahedrons to simulate and track the entire polymerization process of C(N)-A-S-H gel. This innovative method enables researchers to comprehensively understand the formation mechanism of geopolymers, fills the research gap in the lack of full-process polymerization research in traditional simulations, and provides a scientific basis for the optimization and application of subsequent C(N)-A-S-H gel modified materials.

[0035] 2. Solves the lack of the polymerization process of Si and Al tetrahedrons in previous C(N)-A-S-H gel simulation studies. In past studies, many simulations of C(N)-A-S-H gels focused on the gel structures obtained by atom substitution in existing models, while ignoring the influence of the polymerization process on the final structure of the C(N)-A-S-H gel molecular model. The present invention provides a method for exploring the polymerization process on the C(N)-A-S-H gel structure and reveals the microscopic mechanism of the transformation from tetrahedron to gel structure.

[0036] 3. Solves the problem of excessive water molecules generated inside the model during the polymerization of Si and Al tetrahedrons into C(N)-A-S-H gel. The generation of excessive water molecules during the monomer polymerization process will affect the structure of the C(N)-A-S-H gel molecular model and also have an adverse impact on subsequent simulation experimental studies on the C(N)-A-S-H gel molecular model. Adding a water removal stage during the polymerization process avoids this problem and ensures the structural stability of the C(N)-A-S-H gel molecular model and the accuracy of the simulation results.

[0037] 4. It solves the defect that previous modified substances only simulated the formed C(N)-A-S-H gel, but could not simulate the polymerization process. Traditional research methods mainly focused on the performance analysis of the formed C(N)-A-S-H gel and did not deeply study the role of modified substances during the polymerization process. Through the method of the present invention, it is possible to simulate the whole process of the gradual influence of modified substances during the polymerization process of C(N)-A-S-H gel, which not only provides a systematic evaluation method for the optimization of modified substances, but also provides more comprehensive theoretical support for the engineering application of geopolymer materials.

[0038] 5. The method of the present invention combines the influence of GO on C(N)-A-S-H gel with the polymerization process of C(N)-A-S-H gel for the first time in molecular dynamics simulation, and reflects the influence of GO during the polymerization process of C(N)-A-S-H gel. Compared with other atom substitution method modeling, establishing a GO / C(N)-A-S-H gel molecular model by polymerizing GO with monomers can better explore how GO and C(N)-A-S-H gel molecules are connected, rather than relying on speculation.

[0039] 6. The method of the present invention reveals the differential effects of different functional groups of GO on the structure and properties of C(N)-A-S-H gel. And the concept of degree of polymerization is introduced, providing a systematic index for the influence of GO on the polymerization process of C(N)-A-S-H gel. It provides a new direction for the better application of GO in geopolymer materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the principle of the simulated polymerization generation process of the method of the present invention.

[0041] Figure 2 It is a schematic diagram of the C(N)-A-S-H gel molecular models of Examples 1 to 4.

[0042] Figure 3 It is a small-density GO-OH / C(N)-A-S-H gel molecular model of Comparative Example 1, with a large number of voids.

[0043] Figure 4 For Si-O of Examples 1 to 4 b -Si bond angle distribution diagram.

[0044] Figure 5 For Si-O of Examples 1 to 4 b -Al bond angle distribution diagram.

[0045] Figure 6 For Al-O of Examples 1 to 4 b -Al bond angle distribution diagram. Detailed implementation mode

[0046] The present invention will be described in detail below in conjunction with embodiments. The presented content is only partial embodiments of the present invention, not all embodiments.

[0047] The polymerization simulation method of geopolmer gel based on reactive molecular dynamics of the present invention, the specific process of this method is:

[0048] (1) Construct monomers:

[0049] Use modeling software to establish [SiO 4 4- tetrahedrons and [AlO 4 5- tetrahedrons, and connect 4 hydrogen atoms to each tetrahedron. At the same time, add Na 4 5- ions near the [AlO + 4 tetrahedron to generate two monomers, Si(OH) 4 and NaAl(OH) 2 monomer. At the same time, use modeling software to establish the Ca(OH)

[0050] Table 1 Monomer parameters

[0051]

[0052] (2) Establish a precursor model

[0053] Generate a box of a certain size in the modeling software. According to the requirements of a density of 1.80 - 2.20 g / cm 3 , an Si / Al ratio of 2 - 3, and a Ca atom content not greater than the Si atom content, randomly distribute and fill the two monomers, Si(OH) 4 and NaAl(OH) 4 , and the Ca(OH) 2 monomer in the box to form a precursor model. If it is necessary to study the influence of the incorporation of GO or other external admixtures on the polymerization process, the external admixture can be added before filling Si(OH) 4 , NaAl(OH) 4 and Ca(OH) 2 and then fill.

[0054] (3) Simulate the polymerization process

[0055] ​​​​Select the ReaxFF force field file applicable to Si, Al, O, and Ca elements. This force field allows bond breaking and formation, enabling polymerization reactions. Meanwhile, this force field is applicable not only to C(N)-A-S-H gels but also to common modified materials for geopolymers such as organic substances and carbon nanomaterials.

[0056] LAMMPS is a large-scale atomic and molecular parallel simulator mainly used for molecular dynamics simulations. Import the precursor model into LAMMPS, perform energy minimization, and then relax it by equilibration for 100 ps respectively in the NPT ensemble and NVT ensemble at a time step of 0.25 fs and 300 K. After that, heat it from 300 K to 3000 K at a rate of 10 K / ps in the NVT ensemble with a time step of 0.1 fs. Among them, during the 10 ps from 1300 K to 1400 K, simultaneously perform the fix reaxff / species instruction to remove water molecules, and then cool it from 3000 K to 300 K at a rate of 10 K / ps in the NVT ensemble to simulate the polymerization process. The monomers will undergo a polymerization reaction as shown in formula (1) (hydrogen ions do not represent an acidic environment) to generate a C(N)-A-S-H gel molecular model;

[0057] [SiO 4 4+ +Na + +[AlO 4 5- +H + →N-A-S-H+H 2 O

[0058] [SiO 4 4+ +Ca 2+ +[AlO 4 5- +H + →C-A-S-H+H 2 O (1)

[0059] Finally, equilibrate for 300 ps respectively in the NPT ensemble and NVT ensemble at a time step of 0.1 fs and 300 K to obtain a stable C(N)-A-S-H gel molecular model.

[0060] Among them, the purpose of performing a 10-ps water removal process to delete water molecules during the heating process of the polymerization simulation is to simulate the water evaporation caused by the reaction heat during the polymerization process. Not performing water removal throughout the process is to retain the bound water molecules in the C(N)-A-S-H gel. The time of the water removal process can be adjusted according to different research needs.

[0061] ​​​​When studying the influence of GO incorporation on the polymerization process, GO will decompose at high temperature in the simulation and GO does not directly participate in the polymerization reaction. Therefore, GO is grouped before the simulation, and the main carbon atom skeleton part of GO is fixed after energy minimization to prevent GO from decomposing due to heat or the functional groups of GO from detaching.

[0062] (4) Structural inspection

[0063] The structural verification of the C(N)-A-S-H gel molecular model needs to be statistically analyzed through bond lengths and bond angles. Si and Al atoms are the main parts that make up the C(N)-A-S-H gel, while O b is the bridge connecting the main Si and Al atoms in an alternating manner. Therefore, the average bond length of Si-O b , the average bond length of Al-O b , the Si-O b -Si bond angle, the Al-O b -Al bond angle, and the Si-O b -Al bond angle are statistically analyzed. If the statistical values meet the standards, it proves that the structure is reasonable; if the structure is unreasonable, adjust the force field file or change the maximum temperature. Therefore, the structure of the C(N)-A-S-H gel generated by the reaction can be verified according to the bond lengths and bond angles, and the influence of GO on the structure of the C(N)-A-S-H gel can also be analyzed.

[0064] In the model, the biggest difference between the bridging oxygen atom O b and other oxygen atoms is that there are two Si atoms, two Al atoms or one Si atom and one Al atom connected around it. Determine the distance between any two atoms in the model through the coordinate formula (2), and observe the RDF diagram in the C(N)-A-S-H gel in other studies. The Si-O bond length in the C(N)-A-S-H gel is less than the Al-O bond length is less than If this requirement is met, it can be determined that this oxygen atom is connected to the Si atom or the Al atom, and this oxygen atom is determined as the bridging oxygen atom O b .

[0065]

[0066] where d is the distance between atom a and atom b, and x a , y a , z a are the xyz coordinates of atom a, and x b , y b , z b are the xyz coordinates of atom b.

[0067] The said standard is that the average bond length of Si-O in the C(N)-A-S-H gel molecular model is in the range of b and Al-O b The average bond length is in Si-O b -Si bond angle is 136°±5°, Al-O b -Al bond angle is 152°±5°, while Si-O b -Al bond angle is concentrated in the range of 100° to 116°.

[0068] (5) Calculate the degree of polymerization

[0069] Set the degree of polymerization threshold, calculate the degree of polymerization of the C(N)-A-S-H gel molecular model with a reasonable structure. If the degree of polymerization is not less than the degree of polymerization threshold, it meets the polymerization requirements and the simulation results are obtained; if the degree of polymerization is less than the degree of polymerization threshold, it does not meet the polymerization requirements, and the type of force field file is changed or the time of the dehydration process and the initial temperature of the dehydration process are adjusted.

[0070] The main skeleton of the C(N)-A-S-H gel molecule consists of Si-O b -Si, Al-O b -Al, Si-O b -Al bonds. Therefore, the number of O atoms connected to Si and Al atoms in the model is measured to calculate the degree of polymerization of the C(N)-A-S-H gel molecule. In this embodiment, the degree of polymerization should be greater than 60%, which proves a relatively high degree of polymerization. The degree of polymerization calculation formula is as shown in formula (3), where O b is the bridging oxygen atom. b is the bridging oxygen atom.

[0071]

[0072] Among them, f = 4; X is the Si / Al ratio; Q m and Q n are the percentages of the number of Si atoms bridging m oxygen atoms and the number of Al atoms bridging n oxygen atoms respectively, which can be determined by statistics.

[0073] (6) Simulation of the influence of external doping substances on the polymerization process

[0074] Based on the C(N)-A-S-H gel molecular model that meets the requirements determined in the previous steps, study the influence of graphene oxide GO or other external doping substances on the polymerization process. At this time, the monomer construction, precursor model, and relevant parameters for simulating the polymerization process are the same. Before filling Si(OH) 4 , NaAl(OH) 4 and Ca(OH) 2 , add the external doping substance first and then fill it, or fill it randomly together with the monomer;

[0075] During the simulation of the polymerization process, the external admixtures are grouped before the start of the simulation, and the main backbone part of the external admixtures is fixed after energy minimization, and then the polymerization simulation is carried out.

[0076] Furthermore, the bond lengths, bond angles, and degree of polymerization of the stable C(N)-A-S-H gel molecular model when the external admixture is added are determined, and compared with those of the C(N)-A-S-H gel molecular model without the external admixture, so as to determine the influence degree of the external admixture on the polymerization process.

[0077] After determining the model, mechanical property tests can be carried out. Specifically, the tensile simulation process is as follows: the tensile simulation is carried out with a time step of 0.25 fs, and the C(N)-A-S-H gel molecular model is in the NPT ensemble at 300 K, and both ends are fixed Tensile at a strain rate of 0.0001 / ps and output the stress-strain diagram. The maximum stress and Young's modulus can be obtained from the stress-strain diagram, where the Young's modulus is shown in formula (4)

[0078]

[0079] Among them, E is the Young's modulus; σ is the elastic limit stress, and ε is the elastic limit strain, both of which can be determined from the stress-strain diagram.

[0080] Example 1

[0081] The polymerization simulation method of geopolmer gel based on reactive molecular dynamics in this example is as follows:

[0082] (1) Use Materials Studio to establish [SiO 4 4- tetrahedrons and [AlO 4 5- tetrahedrons, and connect 4 hydrogen atoms to each tetrahedron. At the same time, add Na 4 ions near the [AlO 5- + tetrahedron to generate two monomers, Si(OH) 4 and NaAl(OH) 4 . Establish the Ca(OH) 2 monomer as the calcium source of the C(N)-A-S-H gel molecular model.

[0083] (2) Establish a box in Materials Studio. According to the density of 2.00 g / cm 3 and the Si / Ca / Al ratio of 4:3:2, calculate and put Si(OH) 4 , NaAl(OH) 4 ​​​and Ca(OH) 2 They are randomly distributed and filled in the box in quantities of 200, 100, and 150 respectively.

[0084] (3) Select the ReaxFF force field (it is recommended to use a force field file that is applicable to C, H, O, Si, Al, Ca, and Na at the same time. The force field used in this example is: Lianchi, L., et al., Development of a ReaxFF reactive force field for ettringite and study of its mechanical failure modes from reactive dynamics simulations. The journal of physical chemistry. A, 2012.116(15): p.3918 - 25.). Import the precursor model into LAMMPS, perform energy minimization, and then relax it by equilibrating for 100 ps in the NPT ensemble and NVT ensemble at a time step of 0.25 fs and 300 K respectively. After that, heat it from 300 K to 3000 K at a rate of 10 K / ps in the NVT ensemble with a time step of 0.1 fs. Among them, the fix reaxff / species command for removing water molecules is performed simultaneously within 10 ps from 1300 K to 1400 K. Then cool it from 3000 K to 300 K at a rate of 10 K / ps in the NVT ensemble to simulate the polymerization process and obtain the C(N)-A-S-H gel molecular model. Finally, equilibrate for 300 ps in the NPT and NVT ensembles at a time step of 0.1 fs and 300 K respectively to obtain a stable C(N)-A-S-H gel molecular model.

[0085] (4) Structure inspection

[0086] Statistically analyze the average bond length of Si - O, Al - O b the average bond length of Al - O, Si - O b -Si bond angle, Al - O b -Al bond angle, Si - O b -Al bond angle, Si - O b -Al bond angle in the stable C(N)-A-S-H gel molecular model. If the statistical values meet the standards, it proves that the structure is reasonable; if the structure is unreasonable, adjust the force field file or change the maximum temperature, where O b is the bridging oxygen atom;

[0087] The said standards are: the average bond length of Si - O in the C(N)-A-S-H gel molecular model is within b the average bond length of Al - O is within Al - O b the average bond length of Al - O is within Si - Ob -The Si-O bond angle is 136° ± 5°, and the Al-O b -The Al-O bond angle is 152° ± 5°, and the Si-O b -The Al-O bond angles are concentrated in the range of 100° to 116°;

[0088] Obtain a structurally reasonable C(N)-A-S-H gel molecular model that satisfies the verification of bond angle and bond length structure.

[0089] (5) Calculate the number of bridging oxygen atoms connected to Si and Al atoms. According to formula (3), the degree of polymerization of the model is 76.45%, meeting the polymerization requirements.

[0090] (6) Tensile simulation: In LAMMPS, with a time step of 0.25 fs, the C(N)-A-S-H gel molecular model is in the NPT ensemble at 300 K, and both ends are fixed Stretch at a strain rate of 0.0001 / ps. After calculation, the maximum tensile stress and Young's modulus are 3.77 GPa and 21.96 GPa respectively.

[0091] Example 2

[0092] This example studies the polymerization simulation method of geopolymers with GO incorporated into geopolymers (denoted as GO-S). The specific steps are as follows:

[0093] (1) Use Materials Studio to establish [SiO 4 4- tetrahedrons and [AlO 4 5- tetrahedrons, and connect 4 hydrogen atoms to each tetrahedron. At the same time, add Na 4 ions near the [AlO 5- tetrahedron to generate two monomers, Si(OH) + and NaAl(OH) 4 . Establish a Ca(OH) 4 monomer as the calcium source for the C(N)-A-S-H gel molecular model. In addition, establish a monolayer GO with the same number of hydroxyl groups and epoxy groups, each accounting for 8% of the central carbon atoms, and carboxyl groups accounting for 8.8% of the edge carbon atoms, with a size of about 2

[0094] (2) Establish (maintaining the same number and density of monomers as when GO is not incorporated) box in Materials Studio, and place GO parallel to the Z direction ( direction) in the middle of the box; then, according to a density of 2.00 g / cm 3 ​​, calculated according to the Si / Ca / Al ratio of 4:3:2, Si(OH) 4 , NaAl(OH) 4 and Ca(OH) 2 were randomly distributed and filled in the box in quantities of 200, 100, and 150 respectively to obtain a precursor model.

[0095] (3) Select the ReaxFF force field. Import the precursor model into LAMMPS, group the externally doped substances, take the main backbone part of the externally doped substances as a separate group, and the others as a group, and perform energy minimization. Fix the main backbone part of GO in the precursor model (in this embodiment, C and oxygen are substantially fixed), while do not fix functional groups such as hydroxyl groups, epoxy groups, and carboxyl groups. Then, perform relaxation by equilibrating for 100 ps respectively in the NPT ensemble and NVT ensemble at a time step of 0.25 fs and 300 K. After that, heat up from 300 K to 3000 K at a rate of 10 K / ps in the NVT ensemble with a time step of 0.1 fs. Among them, within 10 ps from 1300 K to 1400 K, simultaneously execute the fix reaxff / species instruction to remove water molecules, and then cool down from 3000 K to 300 K at a rate of 10 K / ps in the NVT ensemble to simulate the polymerization process, obtaining a C(N)-A-S-H gel molecular model. Finally, equilibrate for 300 ps respectively in the NPT ensemble and NVT ensemble at a time step of 0.1 fs and 300 K to obtain a stable C(N)-A-S-H gel molecular model.

[0096] (4) After verifying the bond angle and bond length structure, the structure is reasonable.

[0097] (5) By calculating the number of bridging oxygen atoms connected to Si and Al atoms, the degree of polymerization of the model is obtained as 75.65% according to formula (3).

[0098] (6) In LAMMPS with a time step of 0.25 fs, the GO / C(N)-A-S-H gel molecular model is in the NPT ensemble at 300 K, and both ends are fixed and stretched at a strain rate of 0.0001 / ps. The calculated maximum tensile stress and Young's modulus in the direction parallel to GO and perpendicular to GO are 4.09 GPa, 31.49 GPa, 2.64 GPa, and 21.38 GPa respectively, which can strengthen the mechanical properties in the X direction.

[0099] Example 3

[0100] This example studies the polymerization simulation method of geopolymers gel with GO-OH (GO containing only hydroxyl functional groups) incorporated into geopolymers C(N)-A-S-H gel. The specific steps are similar to those in Example 2, and the differences are as follows:

[0101] In step (1), the GO-OH model is established to have hydroxyl functional groups that contain only 10% of the carbon atoms (i.e., the total number of hydroxyl groups in GO is 1 / 10 of the total number of carbon atoms in GO).

[0102] In step (3), the carbon atom backbone part of GO-OH is fixed, and the hydroxyl functional groups are not fixed.

[0103] After verifying the bond angle and bond length structure, the structure is reasonable. By calculating the number of bridging oxygen atoms connected to Si and Al atoms, the degree of polymerization of the model is obtained as 76.66% according to formula (3), and there is a layer of water molecules between the C(N)-A-S-H gel and GO-OH. See Figure 2 , Figure 2 where the gray color represents GO. Compared with other examples, there are more water molecules and smaller voids between GO-OH and the C(N)-A-S-H gel.

[0104] At a time step of 0.25 fs in LAMMPS, the GO / C(N)-A-S-H gel molecular model is in the NPT ensemble at 300 K, with both ends fixed Stretching is performed at a strain rate of 0.0001 / ps, and the maximum tensile stress and Young's modulus in the direction parallel to GO and perpendicular to GO are calculated to be 5.72 GPa, 38.20 GPa, 2.49 GPa, and 18.25 GPa respectively.

[0105] Example 4

[0106] This example provides a method for simulating the polymerization of geopolymers in which GO-COOH (GO containing only carboxyl functional groups) is incorporated into the C(N)-A-S-H gel of geopolymers. The specific steps are similar to those in Example 2, and the differences are as follows:

[0107] In step (1), the GO-COOH model is established to have carboxyl functional groups that contain only 10% of the carbon atoms.

[0108] In step (3), the carbon atom backbone part of GO-COOH is fixed, and the carboxyl functional groups are not fixed.

[0109] After verifying the bond angle and bond length structure, the structure is reasonable. By calculating the number of bridging oxygen atoms connected to Si and Al atoms, the degree of polymerization of the model is obtained as 74.45% according to formula (3). And at this time, it is observed that there is a tetrahedron phenomenon in the model where GO-COOH has carboxyl groups connected to [AlO 4 5- tetrahedrons appear.

[0110] At a time step of 0.25 fs in LAMMPS, the GO / C(N)-A-S-H gel molecular model is in the NPT ensemble at 300 K, with both ends fixed ​Tensile tests were carried out at a strain rate of 0.0001 / ps. After calculation, the maximum tensile stress and Young's modulus in the direction parallel to GO and perpendicular to GO were 4.41 GPa, 32.29 GPa, 1.80 GPa, and 25.84 GPa, respectively.

[0111] From the above four examples, it can be seen that the method of the present invention can establish a C(N)-A-S-H gel molecular model and a GO / C(N)-A-S-H gel molecular model through polymerization process simulation. At the same time, the degree of polymerization and mechanical properties of the models are both excellent. It is possible to explore the influence of the incorporation of different substances on the polymerization results of C(N)-A-S-H gel, and at the same time, the possible interaction mechanism between GO and C(N)-A-S-H gel can also be observed. At the same time, it is also possible to explore the change of the mechanical properties of C(N)-A-S-H gel by GO, and a deeper study can be carried out on the polymerization process of C(N)-A-S-H gel and the influence of modified substances on the polymerization process of C(N)-A-S-H gel. By comparison, it is found that GO containing hydroxyl functional groups has the best promotion effect on both the degree of polymerization and mechanical properties, while GO containing epoxy functional groups has almost no promotion effect on the degree of polymerization and mechanical properties.

[0112] Comparative Example 1

[0113] This comparative example is the same as each step of Example 3, except that in this comparative example, a smaller density of 1.32 g / cm 3 was used for filling in step (2).

[0114] Since the model density is low at this time and there are a large number of voids in the model space (see Figure 3 ), even if tensile simulation is carried out, accurate values cannot be obtained, so mechanical property simulation research cannot be carried out.

[0115] Comparative Example 2

[0116] This comparative example is the same as each step of Example 1. The process of tensile simulation is different:

[0117] In the NPT ensemble at 300 K of the C(N)-A-S-H gel molecular model with a time step of 0.25 fs in LAMMPS, both ends are fixed and tensile tests are carried out at a strain rate of 0.08 / ps. At this time, the obtained tensile stress-strain curve cannot return to zero, and even when the strain is 200%, there is still a tensile stress as high as 3 GPa. Therefore, a reasonable tensile stress-strain curve of GO / C(N)-A-S-H gel cannot be obtained, and the mechanical properties of GO / C(N)-A-S-H gel cannot be studied.

[0118] Comparative Example 3

[0119] This comparative example is the same as each step of Example 1. During the simulated polymerization process, the operation of removing water molecules is not carried out:

[0120] The precursor model is imported into LAMMPS, and energy minimization is performed. Then, relaxation is carried out by equilibrating for 100 ps in the NPT ensemble and the NVT ensemble at a time step of 0.25 fs and 300 K respectively. After that, the temperature is raised from 300 K to 3000 K at a rate of 10 K / ps in the NVT ensemble at a time step of 0.1 fs, and then cooled from 3000 K to 300 K at a rate of 10 K / ps in the NVT ensemble to simulate the polymerization process, obtaining the C(N)-A-S-H gel molecular model. Finally, equilibration is carried out for 300 ps in the NPT and NVT ensembles at a time step of 0.1 fs and 300 K respectively to obtain a stable C(N)-A-S-H gel molecular model.

[0121] Since the step of removing water molecules is not carried out, the water molecules in the model are supersaturated at this time, which affects the progress of the polymerization reaction, and the final degree of polymerization is only 56.45%.

[0122] It can be seen from the above 3 comparative examples that when establishing the C(N)-A-S-H gel molecular model in this application, the setting density of the precursor model and the control of the process of the simulated polymerization process will greatly affect the degree of polymerization of the C(N)-A-S-H gel molecular model, and thus affect the accuracy of the subsequent mechanical property simulation research. In addition, the control of the process parameters of the tensile simulation will also affect the research of its mechanical properties.

[0123] Matters not described in this invention are applicable to the prior art.

Claims

1. A polymerization simulation method for geopolymer gel based on reaction molecular dynamics, characterized in that: The method comprises the following steps: (1) Construction of monomers: Using modeling software to build [SiO4] 4- Tetrahedron and [AlO4] 5- tetrahedron, and connect 4 hydrogen atoms to each tetrahedron, and at the same time in [AlO4] 5- Adding Na near the tetrahedron + ions to generate two monomers, Si(OH)4 and NaAl(OH)4; at the same time, the modeling software was used to establish the Ca(OH)2 monomer as the calcium source for the C(N)-ASH gel molecular model; (2) Establishing a precursor model Generate a box in the modeling software and press 1.80~2.20g / cm 3 Density, Si / Al ratio of 2 to 3, Ca atomic content not greater than Si atomic content, Si(OH)4, NaAl(OH)4 two monomers and Ca(OH)2 monomer are randomly distributed and filled in the box to form a precursor model; (3) Simulation of polymerization process Select the ReaxFF force field file suitable for Si, Al, O, and Ca elements, import the precursor model into LAMMPS, perform energy minimization, and then relax it in the NPT ensemble and NVT ensemble at a time step of 0.25 fs and 300 K for 100 ps respectively; The maximum temperature, dehydration process time and initial temperature of the dehydration process for the simulated polymerization were set. The NVT ensemble was heated from 300K to the maximum temperature at a rate of 10K / ps at a time step of 0.1fs. When the initial temperature of the dehydration process was reached, the fix reaxff / species command for removing water molecules was executed simultaneously until the set dehydration process time was reached, and then the removal of water molecules was stopped. Then, in the NVT ensemble, the temperature is lowered from the highest temperature to 300K at a rate of 10K / ps to simulate the polymerization process. The monomer undergoes a polymerization reaction as shown in formula (1) to generate a C(N)-ASH gel molecular model. Finally, the stable C(N)-ASH gel molecular model was obtained by equilibration in the NPT ensemble and NVT ensemble at 300K with a time step of 0.1fs for 300ps respectively; (4) Structural inspection In the statistically stable C(N)-ASH gel molecular model, Si-O b Average bond length, Al-O b Average bond length, Si-O b -Si bond angle, Al-O b -Al bond angle, Si-O b -Al bond angle, if the statistical value meets the standard, it proves that the structure is reasonable; if the structure is unreasonable, adjust the force field file or change the maximum temperature, where O b For the bridging oxygen atom; The standard is: Si-O b The average bond length is Al-O b The average bond length is Si-O b -Si bond angle is 136°±5°, Al-O b -Al bond angle is 152°±5°, while Si-O b -Al bond angles are concentrated in the range of 100° to 116°; (5) Calculation of degree of polymerization Set the polymerization degree threshold and calculate the polymerization degree for the C(N)-ASH gel molecular model with a reasonable structure. If the polymerization degree is not less than the polymerization degree threshold, the polymerization requirements are met and the simulation results are obtained. If the polymerization degree is less than the polymerization degree threshold, the polymerization requirements are not met, and the force field file type is changed or the dehydration process time and the initial temperature of the dehydration process are adjusted.

2. The method according to claim 1, characterized in that The monomer parameters are: The bond length of Si(OH)4 monomer is The bond angle is 109.5°; the bond length of the NaAl(OH)4 monomer is The bond angle is 109.5°; the bond length of the Ca(OH)2 monomer is The bond angle is 180°.

3. The method according to claim 1, characterized in that During the simulated polymerization process, the NPT ensemble and the NVT ensemble are relaxed sequentially.

4. The method according to claim 1, characterized in that The maximum temperature of the simulated polymerization is 3000K, the dehydration process time is 10ps, and the initial temperature of the dehydration process is 1300K.

5. The method according to claim 1, characterized in that When studying the effect of GO incorporation on the polymerization process, GO will decompose at high temperature in the simulation, and GO does not directly participate in the polymerization reaction. Therefore, GO is grouped before the simulation starts, and the main skeleton part of GO is fixed after energy minimization to prevent GO from being decomposed by heat or the functional groups of GO from detaching.

6. The method according to claim 1, characterized in that The molecular polymerization degree C of C(N)-ASH gel is determined according to formula (3): Where f = 4, X is the Si / Al ratio, Q m With Q n are the percentage of Si atoms bridging m oxygen atoms and the percentage of Al atoms bridging n oxygen atoms, respectively.

7. The method according to claim 1, characterized in that The C(N)-ASH gel molecular model that meets the polymerization requirements can be stretched and simulated. The stretching simulation process is: the C(N)-ASH gel molecular model is in the NPT ensemble at 300K, and the two ends are fixed. Stretching was performed at a strain rate of 0.0001 / ps and a stress-strain diagram was output; the maximum stress and Young's modulus were obtained based on the stress-strain diagram.

8. The method according to any one of claims 1 to 7, characterized in that: When studying the effect of graphene oxide GO or other doping substances on the polymerization process, the doping substances are added before filling Si(OH)4, NaAl(OH)4 and Ca(OH)2, or randomly distributed and filled together with the monomers; In the process of simulating polymerization, the foreign substances are grouped before the simulation starts, and the main skeleton part of the foreign substances is fixed after energy minimization, and then the polymerization simulation is carried out.

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