A method of calculating the wettability of a mineral rough surface
Patent Information
- Application Number
- CN202411585961.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-08
- Publication Date
- 2026-09-22
- Estimated Expiration
- 2044-11-08
AI Technical Summary
1、本发明通过反应分子动力学可以得到高温作用后精确的矿物晶体模型，能够更好的反应高温对其表面润湿性的影响；
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Figure CN119514415B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soil wettability technology, and in particular to a method for calculating the wettability of rough mineral surfaces. Background Technology
[0002] Soil is hydrophilic and mainly composed of minerals (montmorillonite, kaolinite, illite, quartz, etc.). In recent years, it has been found that soils after drought and forest fires have become hydrophobic, meaning that water droplets cannot spontaneously infiltrate the soil. This seriously threatens the safe production of agriculture and animal husbandry, and reduces the soil's water retention and permeability, leading to soil erosion and floods, which seriously threaten people's lives, property, health, and safety.
[0003] Under high temperatures, the crystal structure of the soil surface changes. However, it's impossible to pinpoint exactly where these changes occur within the soil minerals. Molecular dynamics simulations can analyze intermolecular interactions from a molecular perspective. However, empirical force field molecular dynamics infers intermolecular chemical mechanisms through physical reactions, but it cannot precisely investigate the physicochemical transformations of minerals under high temperatures. Reactive molecular dynamics simulations, on the other hand, can monitor the physicochemical transformations of mineral crystal structures under high temperatures. Through reactive molecular dynamics simulations, precise crystal models of minerals after high-temperature exposure can be obtained. Since changes in crystal structure lead to changes in soil surface wettability, obtaining accurate mineral molecular structures is a prerequisite for accurate wettability analysis.
[0004] The most important indicator of mineral surface wettability is the contact angle. In unsaturated soils, the contact angle affects the magnitude of capillary suction, which in turn affects the distribution and movement of water in the soil, as well as the shear strength and stability of the soil.
[0005] Currently, the contact angle can be obtained through experimental methods such as the seated drop method, or through molecular dynamics simulations using empirical force fields (CLAYFF, CVFF, COMPASS, PCFF, etc.). In both experiments and molecular dynamics simulations, the contact angle is usually obtained by fitting the droplet's profile curve. That is, the relevant parameters are determined by fitting the outer contour of the water droplet to a curve, and then the contact angle is calculated.
[0006] Currently, there are many curve fitting methods, such as circular curves and elliptic curves. However, fitting requires manually determining the boundary profile, and different curves selected each time will lead to different results for the water contact angle. Therefore, it can be seen that the method of testing the water contact angle through curve fitting is prone to errors. In addition, current contact angle tests and molecular dynamics simulations are all measured on relatively smooth surfaces, while in real soil, the soil surface is often rough, and current tests and simulations cannot yet adequately characterize the wettability of rough surfaces. Summary of the Invention
[0007] To address the shortcomings of existing technologies, this invention provides a method for calculating the wettability of rough mineral surfaces. This invention can avoid systematic errors caused by rough surfaces, thereby accurately characterizing the surface wettability of minerals after a fire.
[0008] The technical solution of the present invention is: a method for calculating the wettability of a rough mineral surface, comprising the following steps: S1) Calcined mineral crystal models of various soil minerals after being subjected to different temperatures were obtained through reaction molecular dynamics simulations; S2) Construct a water droplet model to obtain a calcined mineral-water droplet model, and simulate the wettability of the calcined mineral crystal surface; S3) The surface tension coefficient of water droplets and the adhesion work of water droplets / mineral interfaces were obtained by using the water droplet model and the calcined mineral-water droplet model. S4) The contact angle of the rough surface is calculated using the Young-Drupé equation, which is then used to characterize the surface wettability of minerals after high-temperature treatment.
[0009] Preferably, in step S1), the construction of the calcined mineral crystal model specifically includes the following steps: S11) Import the cell models of various minerals into Materials Studio software, and perform supercell processing on the mineral cell models to obtain large-size models of various minerals. S12) Energy minimization processing was performed on the large-scale mineral models using LAMMPS to obtain mineral models with reasonable density distribution; S13) Calcination simulation of the mineral model is performed. A 50 Å vacuum layer is established along the positive and negative directions of the Z-axis for the mineral model obtained in step S12, and a 20 Å distillation layer is set at the top and bottom to remove water molecules formed by dehydroxylation of the mineral under high temperature. The mineral model is heated to 378 K, 473 K, 573 K, 673 K, 773 K and 873 K at a constant rate of 10 K / ps, respectively. The simulation is performed at this temperature for 3 ns until the total energy of the system tends to stabilize, and water molecules formed by dehydroxylation of the mineral are removed during this process. S14), and then the temperature is reduced from the specified temperature to 298 K at a constant rate of 10 K / ps, and at 298 K, the system is simulated for 1 ns until the total energy of the system tends to stabilize again, finally obtaining an accurate calcined mineral crystal model.
[0010] Preferably, in step S12), the relaxation of the energy minimization process includes the NVE ensemble with a duration of 100 ps, the NVT ensemble with a duration of 100 ps and a temperature of 298 K, and the NPT ensemble with a duration of 100 ps, a temperature of 298 K and a pressure of 1 atm.
[0011] Preferably, in step S13), the calcination simulation of the mineral model is carried out under the NVT ensemble, the integration step size is selected as 0.25 fs, and the temperature is maintained at 298 K by the Nosé-Hoover method. The temperature damping constant is set to 1 fs to control the heating and cooling rate to 10 K / ps, and the temperature damping constant is set to 100 fs to maintain a constant temperature. Periodic boundaries are set in the X and Y directions, and elastic walls are set in the Z direction boundary.
[0012] Preferably, in step S13), during the calcination simulation of the mineral model, the Reax / c module in the LAMMPS code is used to perform molecular dynamics simulation, and the H / O / Si / Al / Na / Mg reactive force field is selected to define the interaction between the atoms of the mineral.
[0013] Preferably, in step S14), the calcined mineral crystal model includes a calcined kaolinite crystal model, a calcined Na-montmorillonite crystal model, a calcined illite crystal model, and a calcined quartz crystal model.
[0014] Preferably, in step S2), the construction of the water droplet model specifically includes the following steps: S211), Construct a water box model; (S212) A 50.0 Å vacuum layer was set around the water box model. After energy minimization, the temperature of the system was controlled at 296 K, 298 K and 300 K respectively using the Nosé-Hoover method. The water droplet model was obtained by simulating for 1 ns in the NVT ensemble with a time step of 0.25 fs.
[0015] Preferably, in step S2), the calcined mineral-drop model is obtained by merging the droplet model and the calcined mineral crystal model in Lammps.
[0016] Preferably, in step S2), in order not to affect the diffusion motion of the water droplets, the calcined mineral model is made into a 2 a × 2b × 1c supercell.
[0017] Preferably, in step S2), during the wettability simulation, the Reax / c module in the LAMMPS code is used for molecular dynamics simulation. The H / O / Si / Al / Na / Mg reactive force field is selected to define the interaction between the atoms of the mineral and water molecules. All simulations are performed under the NVT ensemble, with an integration step size of 0.25 fs. The temperature is maintained at 298 K using the Nosé-Hoover method, and the boundary is set to three-dimensional periodicity.
[0018] Preferably, in step S2), the calcined mineral-water droplet model includes: calcined kaolinite-water droplet model, Na-montmorillonite-water droplet model, calcined illite-water droplet model, and calcined quartz-water droplet model.
[0019] Preferably, in step S3), the surface tension coefficient of the water droplet... The formula for calculation is: In the formula, The increased free energy of the liquid surface is calculated using the total energy difference between the droplet model and the water box model at equilibrium. The increased liquid surface area is calculated by the difference in surface area between the droplet model and the water box model at equilibrium.
[0020] Preferably, in step S3), the water droplet / mineral interface adhesion function... The formula for calculation is: In the formula, Total energy; and These represent the energy of the separated water and minerals, respectively. This represents the contact area at the water droplet / mineral interface.
[0021] Preferably, in step S4), the contact angle of the rough surface is calculated using the Young-Drupé equation, specifically as follows: S41) Screen the water molecules that are in contact with the substrate and obtain the coordinates of these water molecules; S42) The contact area is calculated using the Alpha Shape algorithm; S43), through The contact angle is calculated using the equation. ,Right now: ; In the formula, Work done on adhesion at the water droplet / mineral interface; is the surface tension coefficient of the water droplet.
[0022] The beneficial effects of this invention are as follows: 1. This invention can obtain an accurate mineral crystal model after high-temperature treatment through reaction molecular dynamics, which can better reflect the effect of high temperature on its surface wettability; 2. This invention calculates the surface tension coefficient of water droplets and the adhesion work at the water droplet / mineral interface separately, and then uses the Young-Drupé equation to accurately calculate the contact angle. This not only allows for rapid characterization of mineral surface wettability, but also reduces errors caused by the contour curve fitting method and avoids systematic errors caused by rough surfaces. As a result, the water contact angle of rough surfaces can be accurately calculated, thereby accurately characterizing the surface wettability of rough minerals after a fire. Attached Figure Description
[0023] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the modeling process for the calcined kaolinite crystal model in an embodiment of the present invention; Figure 3 This is a structural diagram of the calcined kaolinite crystal model simulated according to the present invention; Figure 4 This is a schematic diagram of the modeling of the water droplet model in an embodiment of the present invention; Figure 5 This is a schematic diagram of the calcined kaolinite-water droplet model in an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the calculation of the surface tension coefficient in an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the calculation of the adhesion work at the water droplet / mineral interface in an embodiment of the present invention; Figure 8 This is a schematic diagram of the contact angle measurement using the edge contour method in an embodiment of the present invention. Detailed Implementation
[0024] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings: like Figure 1 As shown, the present invention provides a method for calculating the wettability of a rough mineral surface, comprising the following steps: S1) Calcined mineral crystal models of various soil minerals after being subjected to different temperatures were obtained through reaction molecular dynamics simulations; The construction of the calcined mineral crystal model specifically includes the following steps: S11) Import the cell models of various minerals into Materials Studio software, and perform supercell processing on the mineral cell models to obtain large-size models of various minerals. S12) Energy minimization was performed on the large-scale mineral model using LAMMPS, including the NVE ensemble with a duration of 100 ps, the NVT ensemble with a duration of 100 ps and a temperature of 298 K, and the NPT ensemble with a duration of 100 ps, a temperature of 298 K, and a pressure of 1 atm; thus obtaining a mineral model with a reasonable density distribution. S13) Calcination simulation of the mineral model is performed. A 50 Å vacuum layer is established along the positive and negative directions of the Z-axis for the mineral model obtained in step S12, and a 20 Å distillation layer is set at the top and bottom to remove water molecules formed by dehydroxylation of the mineral under high temperature. The mineral model is heated to 378 K, 473 K, 573 K, 673 K, 773 K and 873 K at a constant rate of 10 K / ps, respectively. The simulation is performed at this temperature for 3 ns until the total energy of the system tends to stabilize, and water molecules formed by dehydroxylation of the mineral are removed during this process. S14), and then the temperature is reduced from the specified temperature to 298 K at a constant rate of 10 K / ps, and at 298 K, the system is simulated for 1 ns until the total energy of the system tends to stabilize again, finally obtaining an accurate calcined mineral crystal model.
[0025] In a preferred embodiment, in step S13), during the mineral model calcination simulation, the Reax / c module in the LAMMPS code is used for molecular dynamics simulation, and the H / O / Si / Al / Na / Mg reactive force field is selected to define the interactions between the mineral atoms. All mineral model calcination simulations are performed under the NVT ensemble, with an integration step size of 0.25 fs. The temperature is maintained at 298 K using the Nosé-Hoover method, with a temperature damping constant set to 1 fs to control the heating and cooling rates at 10 K / ps, and a temperature damping constant set to 100 fs to maintain a constant temperature. Periodic boundaries are set in the X and Y directions, and an elastic wall is set in the Z direction boundary.
[0026] In a preferred embodiment, step S14) includes calcined kaolinite crystal models, calcined Na-montmorillonite crystal models, calcined illite crystal models, and calcined quartz crystal models, such as... Figure 2 and 3 The diagram shows the modeling process of the calcined kaolinite crystal model and the simulated calcined kaolinite crystal model.
[0027] S2) Construct a water droplet model and simulate the wettability of the calcined mineral crystal surface to obtain the calcined mineral-water droplet model; In this embodiment, as Figure 4 As shown, the construction of the water droplet model specifically includes the following steps: S211), Construct a water box model; (S212) A 50.0 Å vacuum layer was set around the water box model. After energy minimization, the temperature of the system was controlled at 296 K, 298 K, and 300 K using the Nosé-Hoover method. The water droplet model was obtained by simulating for 1 ns in the NVT ensemble with a time step of 0.25 fs. In this embodiment, the water box model has dimensions of 31.0 Å × 31.0 Å × 31.0 Å, contains 1000 water molecules, and has a density of 1 g / cm³. 3 .
[0028] Then, by merging the water droplet model and the calcined mineral crystal model in LAMMPS, the calcined mineral-water droplet model is obtained. The calcined mineral-water droplet models obtained in this embodiment include: calcined kaolinite-water droplet model, Na-montmorillonite-water droplet model, calcined illite-water droplet model, and calcined quartz-water droplet model.
[0029] In this embodiment, the surface minerals in the four-layer mineral model obtained by calcination are first retained. To avoid affecting the diffusion of water droplets, a 2 a×2 b×1 c supercell is formed on the surface minerals before and after calcination. Taking kaolinite as an example, after supercell processing of the surface minerals before and after calcination, a kaolinite-water droplet model and a calcined kaolinite-water droplet model are obtained. The kaolinite-water droplet model contains 20408 atoms, and the calcined kaolinite-water droplet model contains 13765~18229 atoms; the structure is 162.536 Å × 125.120 Å × 210.545 Å. See the structural diagram. Figure 5 As shown.
[0030] Furthermore, during the wettability simulation, the Reax / c module in the LAMMPS code was used for molecular dynamics simulation. The H / O / Si / Al / Na / Mg reactive force field was selected to define the interaction between the atoms of minerals and water molecules. All simulations were performed under the NVT ensemble, with an integration step size of 0.25 fs. The temperature was maintained at 298 K using the Nosé-Hoover method, and the boundary was set to three-dimensional periodicity.
[0031] S3) The surface tension coefficient of water droplets and the adhesion work of water droplets / mineral interfaces were obtained by using the water droplet model and the calcined mineral-water droplet model. In this embodiment, in order to calculate the surface tension coefficient of the water droplet In this embodiment, a water box containing 1000 water molecules was constructed, with and without a 50.0 Å vacuum layer. Energy minimization was performed sequentially in LAMMPS, simulating 1 ns in the NVT ensemble with a time step of 0.25 fs. The Nosé-Hoover method was used to control the system temperature at 296 K, 298 K, and 300 K, respectively. The surface tension coefficient of the water droplet is... The formula for calculation is: In the formula, The increased free energy of the liquid surface is calculated using the total energy difference between the droplet model and the water box model at equilibrium. The increased liquid surface area was calculated by the difference in surface area between the droplet model and the water box model at equilibrium; the surface area of the droplet model was obtained by fitting using the Alpha Shape algorithm.
[0032] like Figure 7 As shown, the adhesion function of the water droplet / mineral interface The formula for calculation is: In the formula, Total energy; and These represent the energy of the separated water and minerals, respectively. This represents the contact area at the water droplet / mineral interface.
[0033] S4) The contact angle of the rough surface is calculated using the Young-Drupé equation, thereby characterizing the surface wettability of minerals after high-temperature treatment. Specifically: S41) Screen the water molecules that are in contact with the substrate and obtain the coordinates of these water molecules; S42) The contact area is calculated using the Alpha Shape algorithm; S43), through The contact angle is calculated using the equation. ,Right now: ; In the formula, Work done on adhesion at the water droplet / mineral interface; is the surface tension coefficient of the water droplet.
[0034] In this embodiment, the water contact angle on the surface of calcined kaolinite is used as an example. To verify the accuracy of the calculated contact angle, the curve is also measured using the edge contour method. Figure 8As shown, during measurement, first find the line segment where water / kaolinite contacts the local area in the left figure, then find the outer contour line segment of the water droplet in the right figure, then calculate the included angle between the two line segments, and finally use the average value of the included angle of the line segments as the measured contact angle.
[0035] final The contact angles calculated by the equation and the contact angles obtained by measurement are shown in Table 1. Table 1 Calculation and Measurement of Contact Angle As can be seen from Table 1, through There is a discrepancy between the contact angle calculated by the equation and the measured contact angle. This difference arises because the surface roughness of kaolinite is relatively high after high-temperature treatment, hindering the diffusion of water droplets on the kaolinite surface. Additionally, the water droplet profile is not fully formed, the atomic distribution is highly dispersed, and the contact boundary is artificially defined, leading to many subjective factors in the contact angle measurement process. However, through… The contact angle calculated by the equation can avoid systematic errors caused by rough surfaces, thus accurately characterizing the wettability of rough mineral surfaces after a fire.
[0036] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.
Claims
1. A method for calculating the wettability of a rough mineral surface, characterized in that, Includes the following steps: S1) Calcined mineral crystal models of various soil minerals after being subjected to different temperatures were obtained through reaction molecular dynamics simulations; the construction of the calcined mineral crystal models specifically includes the following steps: S11) Import the cell models of various minerals into Materials Studio software, and perform supercell processing on the mineral cell models to obtain large-size models of various minerals. S12) Energy minimization processing is performed on the large-scale mineral model using LAMMPS to obtain a mineral model with reasonable density distribution; the energy minimization process includes relaxation of the NVE ensemble with a duration of 100 ps, the NVT ensemble with a duration of 100 ps and a temperature of 298 K, and the NPT ensemble with a duration of 100 ps and a temperature and pressure of 298 K and 1 atm, respectively. S13) Calcination simulation of the mineral model was performed. A 50 Å vacuum layer was established along the positive and negative Z-axis directions of the mineral model obtained in step S12), and a 20 Å distillation layer was placed at the top and bottom to remove water molecules formed by dehydroxylation of the mineral under high temperature. The mineral model was heated to 378 K, 473 K, 573 K, 673 K, 773 K, and 873 K at a constant rate of 10 K / ps, respectively. Simulation was performed at these temperatures for 3 ns until the total energy of the system tended to stabilize, during which water molecules formed by dehydroxylation of the mineral were removed. During the calcination simulation of the mineral model, molecular dynamics simulation was performed using the Reax / c module in the LAMMPS code. The H / O / Si / Al / Na / Mg reaction force field was selected to define the interactions between the mineral atoms. All calcination simulations of the mineral model were performed under the NVT ensemble, with an integration step size of 0.25 fs. The temperature was maintained at 298 K using the Nosé-Hoover method, and the temperature damping constant was set to 1 fs to control the heating and cooling rates at 10°C. K / ps, the temperature damping constant is set to 100 fs to maintain a constant temperature; the X and Y directions are set as periodic boundaries, and the Z direction boundary is set as an elastic wall. S14), and then the temperature is reduced from the specified temperature to 298 K at a constant rate of 10 K / ps, and the system is simulated at 298 K for 1 ns until the total energy of the system tends to stabilize again, finally obtaining an accurate calcined mineral crystal model; the calcined mineral crystal model includes a calcined kaolinite crystal model, a calcined Na-montmorillonite crystal model, a calcined illite crystal model and a calcined quartz crystal model. S2) Construct a water droplet model to obtain a calcined mineral-water droplet model, and perform wettability simulation on the surface of the calcined mineral crystals. During the wettability simulation, the Reax / c module in the LAMMPS code is used for molecular dynamics simulation. The H / O / Si / Al / Na / Mg reactive force field is selected to define the interaction between the atoms of the mineral and water molecules. All wettability simulations are performed under the NVT ensemble, with an integration step size of 0.25 fs. The temperature is maintained at 298 K using the Nosé-Hoover method, and the boundary is set to three-dimensional periodicity. S3) The surface tension coefficient of water droplets and the adhesion work of water droplets / mineral interfaces were obtained by using the water droplet model and the calcined mineral-water droplet model. S4) The contact angle of the rough surface is calculated using the Young-Drupé equation, which is then used to characterize the surface wettability of minerals after high-temperature treatment.
2. The method for calculating the wettability of a rough mineral surface according to claim 1, characterized in that: Step S2) involves constructing the water droplet model, specifically including the following steps: S211), Construct a water box model; (S212) A 50.0 Å vacuum layer was set around the water box model. After energy minimization, the temperature of the system was controlled at 296 K, 298 K and 300 K respectively using the Nosé-Hoover method. The water droplet model was obtained by simulating for 1 ns in the NVT ensemble with a time step of 0.25 fs.
3. The method for calculating the wettability of a rough mineral surface according to claim 2, characterized in that: In step S2), the calcined mineral-water droplet model is obtained by merging the water droplet model and the calcined mineral crystal model in LAMMPS.
4. The method for calculating the wettability of a rough mineral surface according to claim 1, characterized in that: In step S3), the surface tension coefficient of the water droplet The formula for calculation is: In the formula, The increased free energy of the liquid surface is calculated using the total energy difference between the droplet model and the water box model at equilibrium. The increased liquid surface area is calculated by the difference in surface area between the droplet model and the water box model at equilibrium. The aforementioned water droplet / mineral interface adhesion function The formula for calculation is: In the formula, Total energy; and These represent the energy of the separated water and minerals, respectively. This represents the contact area at the water droplet / mineral interface.
5. The method for calculating the wettability of a rough mineral surface according to claim 4, characterized in that: In step S4), the contact angle of the rough surface is calculated using the Young-Drupé equation, specifically as follows: S41) Screen the water molecules that are in contact with the substrate and obtain the coordinates of these water molecules; S42) The contact area is calculated using the Alpha Shape algorithm; S43), through The contact angle is calculated using the equation. ,Right now: ； In the formula, Work done on adhesion at the water droplet / mineral interface; is the surface tension coefficient of the water droplet.