Salt concentration polyelectrolyte gel activity coefficient method based on molecular dynamics

Abstract

The invention relates to the technical field of polyelectrolyte gel, in particular to a salt concentration polyelectrolyte gel activity coefficient method based on molecular dynamics, which comprises the following steps: constructing a PES model; defining interaction potential energy parameters in the molecular dynamics model; respectively carrying out molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation by utilizing a large-scale atom-molecule parallel simulator; and inputting files of molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation into a large-scale atom-molecule parallel simulator, and carrying out molecular simulation to obtain an activity coefficient. The invention provides a novel method for testing the ion activity coefficient in polyelectrolyte gel under the action of salt concentration.

Description

Technical Field

[0001] The invention relates to the technical field of polyelectrolyte gel, in particular to a salt concentration polyelectrolyte gel activity coefficient method based on molecular dynamics. Background Art

[0002] Polyelectrolyte gel is a three-dimensional network structure formed by cross-linking of charged polymer chains; when placed in a solvent (usually water), the charged groups on the polymer chains will dissociate to form ions, and counterions of opposite charge will exist in the system.

[0003] Due to the effect of osmotic pressure, polyelectrolyte hydrogels have an ultra-high water absorption rate and can absorb up to 1,000 times their dry volume. Due to their special properties, polyelectrolytes have extensive applications in drug sustained-release systems, tissue engineering and regenerative medicine, biosensors, water treatment and food industries. The properties of ion activity coefficients at different salt concentrations play a key role in the application of polyelectrolyte gels. By studying the changes in ion activity coefficients at different salt concentrations, the sensitivity and selectivity of sensors can be improved, and the accuracy of detection can be enhanced. In battery and energy storage device applications, understanding the changes in ion activity coefficients at different salt concentrations can optimize battery performance, extend battery life and increase energy density.

[0004] Although the ion activity coefficient properties of polyelectrolyte gel under the influence of salt concentration are very important, the numerical measurement is very difficult because the traditional method of testing the ion activity coefficient is based on solution conditions, and polyelectrolyte gel is between solid and liquid, and the traditional method cannot directly measure the activity coefficient of the ions inside it.

[0005] The MET microelectrode technology of Guo et al. can quantitatively measure the potential value inside the gel, thereby calculating the activity coefficient value of the ions in the polyelectrolyte gel; however, this method needs to be controlled under strict experimental conditions, such as the capillary diameter, wall thickness and other process parameters of the microelectrode will have a great influence on the measured value; therefore, it is necessary to study new methods to test the activity coefficient of ions in polyelectrolyte gel under the action of new salt concentration. Summary of the invention

[0006] In view of the shortcomings of the existing methods, the present invention provides a new method for testing the ion activity coefficient in the polyelectrolyte gel under the action of salt concentration.

[0007] The technical solution adopted by the present invention is: the salt concentration polyelectrolyte gel activity coefficient method based on molecular dynamics includes the following steps:

[0008] Step 1: Construct a PES model;

[0009] As a preferred embodiment of the present invention, the PES model is a diamond model;

[0010] As a preferred embodiment of the present invention, the construction of the diamond model includes:

[0011] Set up a molecular chain with several nodes, and add counter ions to the simulation box to make the total charge in the system zero;

[0012] Add several pairs of salt ions to set the relative salt concentration;

[0013] The charges on the monomer units, counterions and salt ions on the polyelectrolyte backbone are set so that the positive and negative charges are balanced and the total charge is 0.

[0014] Step 2: Define the interaction potential energy parameters in the molecular dynamics model;

[0015] As a preferred embodiment of the present invention, the interaction potential energy parameters include: bonding potential energy, van der Waals volume exclusion force and electrostatic force.

[0016] Step 3: Use a large-scale atomic and molecular parallel simulator to perform molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation respectively;

[0017] As a preferred embodiment of the present invention, the definition of molecular dynamics pre-equilibrium simulation includes:

[0018] Read the diamond model file location;

[0019] Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries;

[0020] Set the temperature and dielectric constant for dynamic simulation;

[0021] Set the LAMMPS style and corresponding parameters, including the style of bonded forces and the style of non-bonded forces; set the conjugate gradient method and parameters;

[0022] Set the parameters for molecular dynamics NVE simulation;

[0023] Set the method and content of system balance data output;

[0024] Output pre-balanced data file.

[0025] As a preferred embodiment of the present invention, the definition of molecular dynamics equilibrium volume exploration includes:

[0026] Read pre-balanced data file;

[0027] Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries;

[0028] Set the temperature and dielectric constant for dynamic simulation;

[0029] Set the LAMMPS style and corresponding parameters, including the style of bonded forces and the style of non-bonded forces; set the system volume expansion or reduction parameters;

[0030] Set the parameters for molecular dynamics NVE simulation;

[0031] Output system volume balance data file.

[0032] As a preferred embodiment of the present invention, the activity coefficient calculation includes:

[0033] Read system volume balance data file;

[0034] Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries;

[0035] Set the temperature and dielectric constant for dynamic simulation;

[0036] Set LAMMPS style and corresponding parameters, including: bond force style and non-bond force style; set widom insertion method calculation parameters;

[0037] Set the parameters for molecular dynamics NVE simulation;

[0038] Output activity coefficient data file.

[0039] Step 4: Input the files of molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation into the large-scale atomic and molecular parallel simulator to perform molecular simulation to obtain the activity coefficient.

[0040] As a preferred embodiment of the present invention, a salt concentration polyelectrolyte gel activity coefficient system based on molecular dynamics includes: a memory for storing instructions executable by a processor; a processor for executing the instructions to implement a salt concentration polyelectrolyte gel activity coefficient method based on molecular dynamics.

[0041] As a preferred embodiment of the present invention, a computer readable medium stores a computer program code, and when the computer program code is executed by a processor, the molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method is implemented.

[0042] Beneficial effects of the present invention:

[0043] 1. Solve the problem that it is difficult to measure the internal ion activity coefficient of polyelectrolyte gel under traditional experimental conditions;

[0044] 2. It is easy to operate and saves costs;

[0045] 3. It can provide data basis for future experimental and theoretical research. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flow chart of the molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method of the present invention;

[0047] Figure 2 This is the volume equilibrium simulation structure diagram of the relative salt concentration of 2.9% (30 pairs of salt ions);

[0048] Figure 3 is the ionic activity coefficient of the counter ions and co-ions in the polyelectrolyte gel at different relative salt concentrations. DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with the accompanying drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore it only shows the components related to the present invention.

[0050] like Figure 1 As shown, the molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method includes the following steps:

[0051] Step 1: Use Python to build a PES model (Polyelectrolyte with Salt). The PES model is a polyelectrolyte gel model with different salt concentrations. Figure 2 The diamond model is one of the PES models. Each molecular chain contains 65 nodes. A certain amount of counter ions is added to the simulation box to make the total charge in the system 0. At the same time, salt ions required for different salt concentrations are added, such as 30 pairs of salt ions with a relative salt concentration of 2.9%. Charges are set for the monomer units, counter ions, and salt ions on the main chain of the polyelectrolyte, and the positive and negative charges are balanced. The total charge number is 0. The file of the diamond model is stored as pes.data.

[0052] Step 2: Define the interaction potential parameters in the molecular dynamics model, including bonding potential, van der Waals volume exclusion force and electrostatic force:

[0053] The bond potential is defined as:

[0054]

[0055] Where E1 is the bond energy, K is the FENE spring elastic parameter, R 0 is the equilibrium distance, r1 is the current bond length; in this implementation, K is 30, R 0 is 1.5.

[0056] For non-bonded forces, there are two types: van der Waals volume exclusion force and electrostatic force. The van der Waals volume exclusion force is defined as:

[0057]

[0058] Wherein, E2 is the van der Waals force potential energy, σ and ∈1 are Lennard Jones (LJ) potential parameters, and r2 is the distance between the two particles; in this implementation, σ and ε are both 1.

[0059] The electrostatic force is defined as:

[0060]

[0061] Among them, E3 is the electrostatic force, r c Cut-off radius, C is the energy conversion constant, q i and q j are the charges of the two particles, ε2 is the dielectric constant, and r2 is the distance between the two particles; in this embodiment, ε2 is 0.36.

[0062] Step 3: Use the three in files of the Large Scale Atomic and Molecular Parallel Simulator (LAMMPS) to perform molecular dynamics pre-equilibrium simulation (pre_eq.in), molecular dynamics equilibrium volume exploration (v_eq.in) and activity coefficient calculation (cal.in):

[0063] Step 31, define the molecular dynamics pre-equilibrium simulation pre_eq.in file;

[0064] Step 311, read the location of the diamond model pes.data;

[0065] Step 312: The basic parameters of the molecular dynamics model include unit ， The unit is lj, atom style, the atom style is full, boundary, and the boundary is ppp;

[0066] Step 313, setting the temperature T in the dynamic simulation related parameters to 1.0 and the dielectric constant dielectric to 0.36;

[0067] Step 314, setting the LAMMPS styles and corresponding parameter values ​​of various interaction parameters, including: the style of the bonding force is fene, and the parameter value is: 130.01.51.01.0; the style of the non-bonding force is lj / long / coul / long cut long2.512.0, and the parameter value is: **1.01.01.122;

[0068] Step 315, setting the energy minimization method and parameters to minimize 0.01.0e-8100010000;

[0069] The default energy minimization method is the conjugate gradient method.

[0070] Step 316, set the parameters of molecular dynamics NVE simulation to fix mylgv all langevin${T}${T}0.11530917;

[0071] Step 317, set the system equilibrium data output mode and content to thermo_style custom steptemp press vol, and the output interval to 1000 steps;

[0072] Step 318: Set the output location and name of the pre-balanced data file pequi according to the actual work progress.

[0073] Step 32, respectively define in the molecular dynamics equilibrium volume exploration file v_eq.in;

[0074] Step 321, the location of the pequi file read;

[0075] Step 322, the basic parameters of the molecular dynamics model include unit as lj, atom style as full, and boundary as ppp;

[0076] Step 323, in the parameters related to the dynamic simulation, the temperature T is 1.0, and the dielectric constant dielectric is 0.36;

[0077] Step 324, setting the LAMMPS styles and corresponding parameter values ​​of various interaction parameters, including: the style of the bonding force is fene, and the parameter is 130.01.51.01.0; the style of the non-bonding force is lj / long / coul / long cut long2.512.0, and the parameter is **1.01.01.122;

[0078] Step 325, setting system volume expansion or reduction parameters according to the actual working process, such as the expansion multiple is 1.01, and the reduction multiple is 0.99;

[0079] Step 326, the parameters of the molecular dynamics NVE simulation are fix mylgv all langevin${T}${T}0.11530917;

[0080] Step 327, the system volume balance data output mode and content are fix ave_press all ave / time110001000c_press file press_data.txt, and the output interval is 1000 steps;

[0081] Step 328, setting the output location and name of the vequi file according to the actual working process; the vequi file is a result data file obtained after molecular dynamics simulation based on the v_eq.in file;

[0082] Step 33, respectively define in the activity coefficient calculation file cal.in;

[0083] Step 331, read the location of the vequi file;

[0084] Step 332, the basic system parameters include unit as lj, atom style as full, and boundary as ppp;

[0085] Step 333, in the parameters related to the dynamic simulation, the temperature T is 1.0, and the dielectric constant dielectric is 0.36;

[0086] Step 334, LAMMPS styles and corresponding parameter values ​​of various interaction parameters, including: the style of bonding force is fene, and the parameter is 130.01.51.01.0; the style of non-bonding force is lj / long / coul / long cut long2.512.0, and the parameter is **1.01.01.122;

[0087] Step 335, the calculation parameters of the widom insertion method are fix widomc electrolyte widom100010000212345${T}full_energy charge 1.0;

[0088] Step 336, the parameters of the molecular dynamics NVE simulation are fix mylgv all langevin${T}${T}0.11530917;

[0089] Step 337, the activity coefficient data ac.data is output in the following manner and content: fix out all ave / time110001000f_widomc[1]file ac.data;

[0090] Use the pes.data file and pre_eq.in file to perform molecular dynamics pre-equilibrium and obtain the pre-equilibrium result pequi file;

[0091] Use the pequi file and v_eq.in file to repeatedly perform volume balance simulation, search for the equilibrium volume, and obtain the volume balance result vequi file. The visualization results are as follows: Figure 3 As shown;

[0092] Step 4: Use the pequi file, vequi file and cal file to calculate the ion activity coefficient and obtain the calculation result ac.data; that is, use the parameters in the three files as operating parameters, input them into the large-scale atomic and molecular parallel simulator, and perform molecular simulation to obtain the activity coefficient.

[0093] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method is characterized by: The following steps are involved: Step 1: Construct a PES model; Step 2: Define the interaction potential energy parameters in the molecular dynamics model; Step 3: Use a large-scale atomic and molecular parallel simulator to perform molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation respectively; Step 4: Input the files of molecular dynamics pre-equilibrium simulation, molecular dynamics equilibrium volume exploration and activity coefficient calculation into the large-scale atomic and molecular parallel simulator to perform molecular simulation to obtain the activity coefficient.

2. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 1, characterized in that: The definition of a molecular dynamics pre-equilibrium simulation includes: Read the diamond model file location; Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries; Set the temperature and dielectric constant for dynamic simulation; Set the LAMMPS style and corresponding parameters, including the style of bonded forces and the style of non-bonded forces; Set the conjugate gradient method and parameters; Set the parameters for molecular dynamics NVE simulation; Set the method and content of system balance data output; Output pre-balanced data file.

3. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 1, characterized in that: The definition of the molecular dynamics equilibrium volume exploration includes: Read pre-balanced data file; Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries; Set the temperature and dielectric constant for dynamic simulation; Set the LAMMPS style and corresponding parameters, including the style of bonded forces and the style of non-bonded forces; Set system volume expansion or reduction parameters; Set the parameters for molecular dynamics NVE simulation; Output system volume balance data file.

4. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 1, characterized in that: Activity coefficient calculations include: Read system volume balance data file; Set basic parameters of the molecular dynamics model, including units, atomic style, and boundaries; Set the temperature and dielectric constant for dynamic simulation; Set the LAMMPS style and corresponding parameters, including the style of bonded forces and the style of non-bonded forces; Set the calculation parameters of the widom insertion method; Set the parameters for molecular dynamics NVE simulation; Output activity coefficient data file.

5. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 1, characterized in that: The PES model is a diamond model.

6. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 5, characterized in that: The construction of the diamond model includes: Set up a molecular chain with several nodes, and add counter ions to the simulation box to make the total charge in the system zero; Add several pairs of salt ions to set the relative salt concentration; The charges on the monomer units, counterions and salt ions on the polyelectrolyte backbone are set so that the positive and negative charges are balanced and the total charge is 0.

7. The molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method according to claim 1, characterized in that: The interaction potential parameters include bonding potential, van der Waals volume exclusion force and electrostatic force.

8. A molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient system characterized by: include: a memory for storing instructions executable by a processor; A processor, configured to execute instructions to implement the molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method as described in any one of claims 1 to 7.

9. A computer readable medium storing a computer program code, characterized in that: The computer program code, when executed by a processor, implements the molecular dynamics-based salt concentration polyelectrolyte gel activity coefficient method as described in any one of claims 1 to 7.

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