CN110517733B - Method for constructing dissipative particle dynamic force field - Google Patents
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Abstract
The invention belongs to the field of environmental pollution treatment, and particularly relates to a construction method for simulating a dynamic force field of a dissipative particle of a surfactant solution by using a computer. The method comprises the following steps: 1) establishing a coarse graining model of a surfactant and water molecules; 2) calculating an interaction force parameter between each coarse grained bead by using a Dissipative Particle Dynamics (DPD) theory; 3) establishing a coarse grained structure model of a solution system consisting of a surfactant and water by using Materials Studio software; 4) performing dissipative particle dynamics simulation on the parameters and models obtained in the step (2) and the step (3) by using a DPD module in Materials Studio software to obtain corresponding microstructure property parameters of the surfactant solution; 5) and adjusting interaction parameters among the coarse-grained beads, and optimizing by combining with experimental data of microstructure properties of the surfactant solution to obtain a DPD force field which can be matched with experimental results. The construction method of the invention improves the precision of the coarse grained power field, promotes the development of the coarse grained power field, and has important guiding significance for researching the physicochemical properties of the surfactant in the solution and at the interface.
Description
Technical Field
The invention belongs to the field of environmental pollution treatment, and particularly relates to a construction method for simulating a dynamic force field of a dissipative particle of a surfactant solution by using a computer.
Background
The surfactant is a molecule with hydrophilic and lipophilic groups, has a series of physical and chemical properties of wetting or anti-sticking, emulsifying, air bubble or defoaming, solubilization, dispersion, washing, anticorrosion, antistatic and the like, and is widely applied to daily life and industrial production. However, in the using process, a large amount of wastewater and waste residues containing the surfactant are inevitably discharged into water, soil and other environments, so that serious harm is caused to human bodies and environmental ecosystems, and the problem of environmental pollution is also getting more serious. Therefore, the treatment of industrial and agricultural production and domestic wastewater containing the surfactant is particularly urgent. At present, the treatment of surfactant wastewater has become a research hotspot, and the research on the physicochemical properties of the surfactant in an aqueous solution and at an interface has a main guiding significance.
In the process of diffusion, aggregation and clustering of the surfactant in the aqueous solution, the dynamic change of the structure and the morphology of the system is difficult to directly observe by using the traditional experimental characterization method (such as SEM, TEM, AFM and the like). Computer simulation is a powerful means for studying surface phenomena such as adsorption and diffusion. Molecular or mesoscopic simulations allow for the microscopic investigation of the structure and properties of a substance and directly provide data that cannot be experimentally obtained under extreme conditions. How to accurately explore the interaction force fields between surfactant molecules and between the surfactant molecules and water molecules from a microscopic angle by using a DPD simulation method so as to represent the microscopic properties of a surfactant solution, and the method has important significance for researching the physical and chemical properties of a surfactant system and the application of the surfactant system in the fields of chemistry and chemical industry, biology, medicine and the like.
Disclosure of Invention
Aiming at the problem that the development method of the force field related to the surfactant solution system in the prior art is blindly provided, the invention provides an optimized development method of the force field for researching the interaction force of the surfactant solution system, so as to improve the precision of the coarse grained force field and promote the development of the coarse grained force field.
A method for developing a dissipative particle dynamic force field of a surfactant solution comprises the following steps:
(1) establishing a coarse granulation model of surfactant molecules and water molecules in Materials Studio software;
(2) calculating interaction force parameters among the coarse grained beads in the coarse grained model in the step (1) to obtain corresponding interaction force parameter ranges;
(3) constructing a coarse granulation model of the surfactant solution in Materials Studio software;
(4) and (3) obtaining parameters and models in the step (2) and the step (3), performing dissipative particle dynamics simulation by using a DPD module in Materials Studio software, recording coordinates and motion tracks of the coarse-grained beads after the system reaches balance, analyzing bond length and interaction energy among the beads according to an Analysis function in the DPD module, directly observing the dynamic change process of the structure and the morphology of a simulation system by combining with Animation in the Materials Studio software, and obtaining corresponding microstructure property parameters of the surfactant solution.
(5) Repeatedly fine-tuning the interaction force parameters among the beads in the numerical range of the interaction force parameter range table to obtain microstructure property parameter simulation values of the surfactant solution under the interaction forces with different strengths; and comparing the simulation value with corresponding experimental data until the simulation value is consistent with the experimental data, and determining that the interaction force parameter under the condition is the optimized DPD force field parameter of the surfactant solution.
Further, the coarse grain model established in step (1) is as follows: water bead W is 3H2O, the surfactant molecule is HnTmConsists of n hydrophilic beads H and m hydrophobic beads T.
Further, the surfactant is sodium alkyl sulfonate containing sulfonic acid groups.
Further, the calculation formula of the interaction parameter between the coarse grained beads in the step (2) is as follows:
wherein, aiiRepresents the interaction force parameter between identical DPD beads;
aijrepresents the interaction force parameter between different DPD beads;
in the formula, NmRepresents the level of coarsening in the DPD simulation, i.e., the number of water molecules contained in one DPD bead;
kBt represents an energy unit in the DPD simulation;
ρ represents the density of the DPD simulation system;
χijrepresents the Flory-Huggins parameter between different DPD beads.
Further, the parameters of the interaction force between the beads obtained in the step (2) are as follows: the parameter range of the interaction force of the water beads W and the hydrophilic beads H is 65-75.8; the interaction force parameter range of the water beads W and the hydrophobic beads T is 90-104; the interaction force parameter range between the hydrophilic bead H and the hydrophobic bead T is 84-124, the interaction force parameter between the water beads W is 78, the interaction force parameter between the hydrophobic beads T is 78, and the interaction force parameter between the hydrophilic bead H is 86.7.
Further, the coarse grained model in the step (3) is constructed by a DPD module in Materials Studio software, and a cube box with a system of x ═ y ═ z coordinates is adopted, and water beads W and surfactant molecules HnTm are added into the box, wherein the number of the water beads and the surfactant molecules is converted according to the concentration of the surfactant.
Further, the specific parameters of the DPD dynamics simulation in step (4) are set as follows: the total simulation time is 200000 steps, the temperature is set to 298K, the time step is set to 0.05, and one simulation result is output every 1000 steps.
Further, the microstructure property parameters of the surfactant in the steps (4) and (5) comprise one or more of a sub-aggregation number, a critical micelle concentration and an aggregation morphology.
Further, the experimental data in the step (5) is the critical micelle concentration, the number of sub-aggregates or the micelle aggregation morphology obtained by experiments in the references.
The invention has the advantages and positive effects that: compared with the prior development, the invention provides a method for establishing and optimizing microstructure properties based on the surfactant by utilizing a dissipative particle dynamics simulation technology, improves the precision of a coarse graining force field, expands the application of the coarse graining force field, and has important guiding significance for researching the physicochemical properties of the surfactant in the solution and at an interface.
Drawings
FIG. 1 shows a coarse water molecule granulation model constructed in Materials Studio software;
FIG. 2 shows a coarse granulation model H1T2 of sodium hexaalkyl sulfonate molecules constructed in Materials Studio software;
FIG. 3 shows a coarse granulation model H1T3 of sodium nonaalkylsulfonate molecules constructed in Materials Studio software;
FIG. 4 shows a coarse granulation model H1T4 of sodium dodecyl sulfate molecules constructed in Materials Studio software;
FIG. 5 shows a coarse particle size model H1T5 of sodium pentadecylsulfonate molecules constructed in Materials Studio software;
FIG. 6. aggregation morphology of surfactant H1T2 solution in equilibrium obtained under parametric conditions.
Detailed Description
For better understanding of the present invention, the technical solutions of the present invention will be described in further detail with reference to specific embodiments, but the scope of the present invention is not limited to the scope shown in the examples.
Example (b):
(1) in this example, surfactant molecules represented by sodium alkylsulfonate are selected, and a coarse grained model of the surfactant molecules and water molecules is first established, that is, coarse grained DPD beads are defined as follows: water bead W (3H)2O) the coarse grain model is shown in FIG. 1; according to the structure of sodium alkylsulfonate, the surfactant molecule consists of n hydrophilic beads H (-OSO)3Na) and m hydrophobic beads T (end CH)3-CH2-CH2-or a middle-CH2-CH2-CH2-) composition (DPD coarse grained models of sodium hexaalkylsulfonate, sodium nonaalkylsulfonate, sodium dodecylsulfonate, sodium pentadecylsulfonate are represented as H1T2, H1T3, H1T4, H1T5, respectively), and DPD coarse grained structural models thereof are shown in FIGS. 2 to 5.
(2) Calculating interaction force parameters among the coarse-grained beads in the coarse-grained model in the step (1) to obtain corresponding interaction force parameter ranges, and calculating the interaction force parameters among the coarse-grained beads according to Flory-Huggins parameters of the beads, wherein the calculation formula is as follows;
wherein, aiiRepresents the interaction force parameter between identical DPD beads;
aijrepresents the interaction force parameter between different DPD beads;
in the formula, NmRepresents the level of coarse grain in the DPD simulation, namely: the number of water molecules contained in one DPD bead;
kBt represents an energy unit in the DPD simulation;
ρ represents the density of the DPD analog system, where ρ is 3;
χijthe Flory-Huggins parameters between different DPD beads are shown and obtained in the reference.
The calculated interaction force parameters are shown in the table below.
| aij/aii | H | T | W |
| H | 86.7 | ||
| T | 84-124 | 78 | |
| W | 65-75.8 | 90-104 | 78 |
Wherein, aHTRepresenting the interaction force between hydrophilic groups and hydrophobic groups of the surfactant, ranging from 84 to 124; a isWHShowing the interaction force between the water beads and the hydrophilic group beads of the surfactant,the range is 65-75.8; a isWTRepresenting the interaction force between the water beads and the hydrophobic base beads of the surfactant, ranging from 90 to 104.
(3) The coarse grained structure model of the surfactant solution was constructed in the DPD module in Materials Studio software as follows: and a cubic box with system coordinates of x, y, z and 20, wherein water beads W and surfactant molecules H1Tm (m is 2,3,4 and 5) are added into the box, and the number of the water beads and the surfactant molecules is converted according to the concentration of the surfactant.
(4) Performing dissipative particle dynamics simulation on the established surfactant solution coarse granulation model and the obtained force field parameters by using a DPD module in the materials studio software, wherein the specific parameters of the DPD dynamics simulation are set as follows: the total simulation time is 200000 steps, the temperature is set to 298K, the time step is set to 0.05, and one simulation result is output every 1000 steps. After the system is balanced, the coordinates and the motion trail of each coarse-grained bead are recorded, the bond length and the interaction energy among the beads are analyzed according to the Analysis function in the DPD module, the dynamic change process of the structure and the morphology of the simulation system is directly observed by combining with Animation in material Studio software, and corresponding microstructure property parameters of the surfactant solution are obtained.
(5) Adjusting the interaction strength between the surfactant and water according to the parameters among the beads in the table 1 to obtain microstructure property parameter simulation values of the surfactant solution under the interaction forces with different strengths; and comparing the simulation value with the experimental data until the simulation value is consistent with the experimental data, and determining that the interaction force parameter under the condition is the optimized DPD force field parameter of the surfactant solution. The aggregation morphology of the H1T2 solution system after the system reaches the equilibrium state under the optimized parameter conditions is shown in FIG. 6, wherein the black beads represent H and the white beads represent T.
Although the preferred embodiments of the present patent have been described in detail, the present patent is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present patent within the knowledge of those skilled in the art.
Claims (8)
1. A method for constructing a dynamic force field of a dissipative particle of a surfactant solution is characterized by comprising the following steps: the method comprises the following steps:
(1) establishing a coarse granulation model of surfactant molecules and water molecules in Materials Studio software;
(2) calculating interaction force parameters among the coarse grained beads in the coarse grained model in the step (1) to obtain corresponding interaction force parameter ranges, wherein the calculation formula of the interaction force parameters among the coarse grained beads is as follows;
wherein: a isiiRepresents the interaction force parameter between identical DPD beads;
aijrepresents the interaction force parameter between different DPD beads;
in the formula: n is a radical ofmRepresents the level of coarse grain in the DPD simulation, namely: the number of water molecules contained in one DPD bead;
kBt represents an energy unit in the DPD simulation;
ρ represents the density of the DPD simulation system;
χijrepresents Flory-Huggins parameters among different DPD beads;
(3) constructing a coarse granulation model of the surfactant solution in Materials Studio software;
(4) obtaining parameters and models in the step (2) and the step (3), performing dissipative particle dynamics simulation by using a DPD module in Materials Studio software, recording coordinates and motion tracks of the coarse-grained beads after the system reaches balance, analyzing bond length and interaction energy among the beads according to an Analysis function in the DPD module, directly observing a dynamic change process of the structure and the morphology of a simulation system by combining with Animation in the Materials Studio software, and obtaining corresponding microstructure property parameters of a surfactant solution;
(5) repeatedly fine-tuning the interaction force parameters among the beads in the numerical range of the interaction force parameter range table to obtain microstructure property parameter simulation values of the surfactant solution under the interaction forces with different strengths; and comparing the simulation value with corresponding experimental data until the simulation value is consistent with the experimental data, and determining that the interaction force parameter under the condition is the optimized DPD force field parameter of the surfactant solution.
2. The method of claim 1, wherein the method comprises the steps of: the coarse grain model established in the step (1) is as follows: the water beads W are 3H2O, the surfactant molecules are HnTm and consist of n hydrophilic beads H and m hydrophobic beads T.
3. The method of claim 1, wherein the method comprises the steps of: the surfactant is sodium alkyl sulfonate containing sulfonic acid groups.
4. The method of claim 3, wherein the method comprises the steps of: the parameter range of the interaction force among the beads obtained in the step (2) is as follows: the parameter range of the interaction force of the water beads W and the hydrophilic beads H is 65-75.8; the interaction force parameter range of the water beads W and the hydrophobic beads T is 90-104; the interaction force parameter range between the hydrophilic bead H and the hydrophobic bead T is 84-124, the interaction force parameter between the water beads W is 78, the interaction force parameter between the hydrophobic beads T is 78, and the interaction force parameter between the hydrophilic bead H is 86.7.
5. The method of claim 1, wherein the method comprises the steps of: the coarse graining model in the step (3) is constructed through a DPD module in Materials Studio software, a cube box with a system of x, y, z coordinates is adopted, water beads W and surfactant molecules HnTm are added into the box, and the quantity of the water beads and the surfactant molecules is converted according to the concentration of the surfactant.
6. The method of claim 1, wherein the method comprises the steps of: the specific parameters of the DPD dynamics simulation in step (4) are set as follows: the total simulation time is 200000 steps, the temperature is set to 298K, the time step is set to 0.05, and one simulation result is output every 1000 steps.
7. The method for constructing the dynamic force field for dissipating the particles from the surfactant solution according to claim 1, wherein the microstructure property parameters of the surfactant in the steps (4) and (5) comprise one or more of a sub-aggregation number, a critical micelle concentration and an aggregation morphology.
8. The method for constructing the dynamic force field for dissipating the particles from the surfactant solution according to claim 1, wherein the experimental data in the step (5) is the critical micelle concentration, the sub-aggregation number or the micelle aggregation morphology obtained by experiments in the literature.
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