A method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings

Abstract

The invention discloses a method for simulating and quantifying the interchain association and chain mobility of a zwitterionic polymer brush coating, comprising the following steps: constructing a zwitterionic polymer brush coating model and setting the model; using an MD method to simulate and calculate the atomic motion and distribution in the zwitterionic polymer brush coating model, recording the position and velocity information of each atom at each simulation moment, until obtaining the atomic trajectory information of a long-time simulation under set conditions; and analyzing and obtaining the structural parameters of the zwitterionic polymer brush coating model according to the atomic velocity and position information obtained by calculation, including the association between chains in the zwitterionic polymer brush coating and the mobility information of the polymer chain.

Description

Technical Field

[0001] The invention relates to the technical field of molecular dynamics simulation, and relates to a method for simulating and quantifying the interchain association and chain mobility of a zwitterionic polymer brush coating, and specifically relates to a method for quantifying the interchain association and chain mobility of a zwitterionic polymer brush coating based on molecular dynamics simulation. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The molecular structure of zwitterionic polymers contains equal amounts of positive and negative charged groups, making the entire molecule neutral. This charge balance can reduce electrostatic attraction and reduce nonspecific adsorption with biomolecules (such as proteins and cells), thereby inhibiting the formation of biofilms. In contrast, single-charged polymers tend to be easily electrostatically attracted to biomolecules with opposite charges, leading to the formation of biofilms, while the charge balance property of zwitterionic polymers effectively reduces the occurrence of this phenomenon. In addition, in the molecular structure of zwitterionic polymers, positive and negative charges are usually evenly distributed, minimizing the dipole moment of the entire molecule. This property of minimizing dipoles enhances the interaction with water molecules and promotes the formation of hydration shells. Compared with traditional non-ionic hydrophilic materials, zwitterionic polymers achieve stronger anti-biological adhesion properties through the hydration effect. This gives zwitterionic polymers significant advantages in anti-biological molecule adhesion in the fields of medical equipment, ship coatings, marine coatings, etc. In addition, the hydration layer formed by the strong hydration of the zwitterionic polymer brush coating also has a special role: on the one hand, as a polar molecule, the water molecules in the aqueous solution form a hydration layer around the charge, which reduces the self-energy surrounding the charge, so the water molecules in the hydration shell require a lot of energy to peel off, so the polymer brush coating can bear a large normal pressure. On the other hand, the water confined in the hydration layer is not fixed, but maintains a high degree of fluidity, and can still shear flow like bulk water under surface shear conditions, thereby showing lubrication properties. Therefore, the surface modified by the zwitterionic polymer brush coating also has excellent lubrication properties.

[0004] However, because zwitterionic polymer brush coatings contain both anionic and cationic groups, chains will associate due to the electrostatic interaction between anionic and cationic groups. Excessive interchain association will weaken the structural stability of the polymer brush coating, and even cause the overall collapse of the polymer brush coating, thereby increasing the surface roughness of the polymer brush coating, deteriorating the surface hydrophilicity, and reducing or even losing the lubrication and anti-adhesion effects. At the same time, the interchain association of zwitterionic polymer brush coating chains will directly affect the mobility of polymer brush coating chains, and the mobility of polymer chains is of decisive significance to the lubrication and anti-adhesion properties of polymer brush coatings.

[0005] However, it is difficult to determine the interchain association of zwitterionic polymer brush coatings using current experimental methods. Only in certain thicknesses is it found that zwitterionic polymer brush coatings collapse, which makes the surface wettability worse, which is speculated to be caused by interchain association. In addition, the mobility of zwitterionic polymer brush coating chains is even more difficult to characterize experimentally. These technical difficulties directly make it difficult to promote the use of zwitterionic polymer brush coatings in practical engineering applications. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings, so as to solve the problem that it is difficult to achieve quantitative research on the interchain association and polymer chain mobility of zwitterionic polymer brush coatings in the existing molecular dynamics simulation technology.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings comprises the following steps:

[0009] Construct a zwitterionic polymer brush coating model and set up the model;

[0010] The MD method is used to simulate and calculate the atomic motion and distribution in the zwitterionic polymer brush coating model, and the position and velocity information of each atom at each simulation moment is recorded until the atomic trajectory information of long-term simulation under set conditions is obtained;

[0011] Based on the atomic velocity and position information obtained by calculation, the structural parameters of the zwitterionic polymer brush coating model are analyzed and obtained, including the association between the chains of the zwitterionic polymer brush coating and the mobility information of the polymer chains.

[0012] In some embodiments, when constructing a zwitterionic polymer brush coating model, the molecular model of the zwitterionic polymer brush coating material is drawn using Materials Studio software, and the structure is optimized to obtain the CHARMM force field potential energy parameters of the zwitterionic polymer brush coating material (through the CHARMM GUI website (https: / / charmm-gui.org / )), and the zwitterionic polymer brush coating model is constructed using VMD software and solvation treatment is performed.

[0013] Preferably, the substrate of the zwitterionic polymer brush coating model is a silicon substrate, and a segment of the zwitterionic polymer is fixed on the silicon substrate and arranged perpendicular to the silicon substrate.

[0014] Further preferably, the length of the zwitterionic polymer chain is controllable to simulate the effect of the thickness of the zwitterionic polymer brush coating on the interchain association and the mobility of the polymer brush coating chains.

[0015] Further preferably, the distance between the chains of the zwitterionic polymer is controllable to simulate the effect of the grafting density of the zwitterionic polymer brush coating on the interchain association and the mobility of the polymer brush coating chains.

[0016] Further preferably, the material of the zwitterionic polymer brush coating is phosphorylcholine, carboxybetaine or phosphorylcholine, so as to explore the influence of different zwitterionic polymer materials on the interchain association of the polymer brush coating and the mobility of the polymer brush coating chain.

[0017] Preferably, during the solvation treatment, ions are added to the solution environment, and the ions are selected from chloride ions, sodium ions, calcium ions, magnesium ions or sulfate ions, so as to explore the effects of solution environments with different valence states and different ionic strengths on the association between zwitterionic polymer brush chains and the mobility of polymer brush coating chains.

[0018] In some embodiments, the parameters for setting up the model include boundary conditions of the calculation system, potential function selection, energy minimization, relaxation balance, and output parameters.

[0019] Preferably, when setting up the model, the three boundaries of the simulation system, X, Y, and Z, are set as periodic boundaries, and the cutoff distance of the short-range Lennard-Jones interaction is set to The time step was 2 fs; energy minimization was performed for 50,000 steps to eliminate poor contacts and reduce system energy; the relaxation time was not less than 2 ns.

[0020] In some embodiments, when the MD method is used to simulate the atomic motion and distribution in the zwitterionic polymer brush coating model, the simulation time is not less than 30 ns.

[0021] In some embodiments, when performing the analysis, the distance between the carbon atom on the quaternary amino group of the zwitterionic polymer monomer and the oxygen atom on the anionic group is counted to characterize the interchain association of the zwitterionic polymer in the zwitterionic polymer brush coating.

[0022] Preferably, interchain association occurs when the distance between the carbon atom on the quaternary amino group of the zwitterionic polymer monomer and the oxygen atom on the anionic group is smaller than the distance between the carbon atom on the quaternary amino group and the oxygen atom on the anionic group of the same zwitterionic monomer.

[0023] The distance between carbon atoms and oxygen atoms includes two categories, one is the distance D1 between carbon atoms and oxygen atoms on different polymer brush coating chains, and the other is the distance D2 between carbon atoms and oxygen atoms on the same polymer zwitterionic monomer. Since there are 2-3 methylene groups between the anion and cation groups in the zwitterionic monomer, this limits the anion and cation groups on the same monomer from being infinitely close. However, the anion and cation groups on different chains do not have such a steric hindrance effect and are closer. Therefore, D1 is smaller than D2, and the appearance of D1 is entirely due to interchain association. Therefore, the anion and cation groups within the distance range less than D2 must come from different polymer chains, so it can be used as an indicator to quantify the interchain association of zwitterionic polymer brush coating chains.

[0024] In some embodiments, when performing the analysis, the position distribution of the center of mass of the top zwitterionic monomer of the zwitterionic polymer chain in the zwitterionic polymer brush coating on the XY cross section during the statistical simulation process is used to characterize the mobility of the polymer brush coating chain. In order to quantify the migration radius, a circular area covering 90% of the distribution points on the XY plane is defined as the distribution radius. The larger the distribution radius, the higher the mobility.

[0025] The wider the distribution of the center of mass of the zwitterionic monomer on the XY cross section, the higher the mobility of the polymer brush coating chain.

[0026] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0027] The method provided by the present invention for quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings based on molecular dynamics simulation provides a clear and quantifiable method for the interchain association and chain mobility of zwitterionic polymer brush coatings. The quantitative characterization of the interchain association and chain mobility of zwitterionic polymer brush coatings can provide guidance for the design of zwitterionic polymer brush coatings. The interchain association and chain mobility of different polymer brush coating materials are compared and studied to optimize the polymer brush coating materials. In addition, the thickness and grafting density of the polymer brush coating can be controlled to optimize the structure of the polymer brush coating to achieve the required interchain association rate and chain mobility. In addition, the parameters such as the ionic strength and ionic valence of the salt solution and the ambient temperature can be adjusted to explore the influence of the salt solution and the ambient temperature on the interchain association rate and chain mobility of the polymer brush coating, and determine the applicability of the polymer brush coating in different environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1The chemical structural formula of the molecular dynamics model constructed by Example 1 and Example 2 provided by the present invention;

[0030] Figure 2 The molecular dynamics model constructed according to Example 1 provided by the present invention;

[0031] Figure 3 A schematic diagram of the interchain association of zwitterionic polymer brush coatings of different materials provided in Example 1 of the present invention;

[0032] Figure 4 A comparison chart of the interchain association rates of polymer brush coatings of different materials provided in Example 1 of the present invention;

[0033] Figure 5 Schematic diagram of chain mobility of zwitterionic polymer brush coatings of different materials provided in Example 1 of the present invention;

[0034] Figure 6 The mobility of zwitterionic polymer brush coatings of different materials provided in Example 1 of the present invention;

[0035] Figure 7 The interchain association rate of the zwitterionic polymer brush coating with different grafting densities provided in Example 2 of the present invention;

[0036] Figure 8 The mobility of zwitterionic polymer brush coatings with different grafting densities in Example 2 provided by the present invention. DETAILED DESCRIPTION

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0038] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0039] Example 1

[0040] It is worth noting that this embodiment extracts and analyzes the interchain association rate and chain mobility of polymer brush coatings of different materials, and then prefers zwitterionic polymer brush coating materials. Since there are many kinds of polymer brush coating materials, but the molecular dynamics modeling and simulation process of the zwitterionic polymer brushes of each material are consistent, this embodiment models and simulates three common zwitterionic polymer brush coating materials. This embodiment uses methacryloylethyl carboxybetaine polymer brush coating (represented by PCBMA in the figure), methacryloylethyl phosphorylcholine polymer brush coating (represented by PMPC in the figure), and methacryloylethyl sulfonobetaine polymer brush coating (represented by PSBMA in the figure) as examples for explanation. The specific modeling and simulation process, data extraction and analysis results are as follows:

[0041] The molecular models of methacryloylethyl carboxybetaine polymer brush coating chains, methacryloylethyl phosphorylcholine polymer brush coating chains, and methacryloylethyl sulfobetaine polymer brush coating chains were drawn using Materials Studio software. Each polymer brush coating chain is polymerized from 15 monomers and the structure is optimized. The chemical structure of the polymer brush coating monomer and the molecular model of the polymer chain are shown in Figure 1. Figure 1 The CHARMM force field potential energy parameters of the three polymer brush coating materials were obtained through the CHARMM GUI website (https: / / charmm-gui.org / ), and the polymer brush coating model was constructed through VMD software. Water molecules were added to the polymer brush model to change the model size to The rectangular box of the polymer brush coating model is obtained as Figure 2 The distance between polymer chains in the polymer brush coating model is 1.5 nm, and each molecular dynamics model contains 16 polymer brush coating chains.

[0042] The simulation parameters of the above models were set respectively. The three boundaries of the simulation system X, Y, and Z were set as periodic boundaries, and the cutoff distance of the short-range Lennard-Jones interaction was set as The time step is 2 fs. Energy minimization is performed for 50,000 steps to eliminate bad contacts and reduce the system energy. The relaxation time is 2 ns.

[0043] The above models were simulated and calculated respectively. The MD method is mainly based on classical Newtonian mechanics to simulate the movement and distribution of atoms in the calculation system. That is, the distance between atoms and the potential energy function determine the force between atoms, which in turn leads to the movement and redistribution of atoms. The position and velocity information of each atom at each simulation moment is recorded, and the cycle is repeated until the atomic trajectory information of long-term simulation under certain conditions is obtained; the simulation time is 32ns.

[0044] Data analysis, based on the atomic speed and position information obtained by calculation, analyzes the structural parameters of the object system, etc., focusing on analyzing the association between polymer brush coating chains and the mobility information of polymer chains.

[0045] In order to realize the interchain association of polymer brush coating, the distance between the carbon atom on the quaternary amino group of the zwitterionic monomer and the oxygen atom on the anionic group is counted to represent the interchain association of polymer brush coating. The distance between carbon atoms and oxygen atoms includes two types: one is the distance D1 between carbon atoms and oxygen atoms on different polymer brush coating chains, and the other is the distance D2 between carbon atoms and oxygen atoms on the same zwitterionic monomer, such as Figure 3 . Since there are 2-3 methylene groups between the anion and cation groups in the zwitterionic monomer, this limits the anion and cation groups on the same monomer from being infinitely close. However, the anion and cation groups on different chains do not have such a steric hindrance effect and are closer. Therefore, D1 is smaller than D2, and the appearance of D1 is entirely due to interchain association. Therefore, the anion and cation groups within a distance range less than D2 must come from different polymer chains, and can therefore be used as an indicator to quantify the interchain association of zwitterionic polymer brush coating chains. By comparison, it can be found that the three zwitterionic polymer brush coatings PCBMA, PMPC, and PSBMA all have interchain association.

[0046] Figure 4 is the association rate data, with a distance less than The distribution probability extreme value quantifies the association rate when Figure 4 In the area represented by the black box, it is found that the PCBMA polymer brush has the highest association rate, while the PSBMA polymer brush has the lowest association rate.

[0047] Data analysis, in order to achieve quantitative characterization of the mobility of the zwitterionic polymer brush coating chain, the position distribution of the center of mass of the top zwitterionic monomer of the polymer brush coating chain on the XY cross section during the statistical simulation process can characterize the mobility of the polymer brush coating chain. The position of the top monomer of the polymer brush coating chain at the initial position of the simulation and the position at the end of the simulation has significant differences, such as Figure 5 As shown. The wider the distribution of the center of mass of the zwitterionic monomer on the XY cross section, the higher the mobility of the polymer brush coating chain. By comparison, it is found that the chain mobility of the PSBMA polymer brush coating is the lowest, while the chain mobility of the PMPC polymer brush coating is the highest, as shown in Figure 6 shown.

[0048] Example 2

[0049] It is worth noting that this embodiment extracts and analyzes the interchain association rate and chain mobility of polymer brush coatings with different grafting densities, thereby optimizing the grafting density of zwitterionic polymer brush coatings. Therefore, this embodiment takes methacryloylethyl carboxybetaine polymer brush coating (represented by PCBMA in the figure) as an example for explanation. The specific modeling and simulation process, data extraction and analysis results are as follows:

[0050] The methacryloylethyl carboxybetaine polymer brush coating chain was drawn by Materials Studio software. Each polymer brush coating chain is composed of 15 monomers and the structure is optimized. The chemical structure of the methacryloylethyl carboxybetaine polymer brush coating monomer and the molecular model of the polymer chain are shown in Figure 1. Figure 1 As shown. The CHARMM force field potential energy parameters of the three polymer brush coating materials were obtained through the CHARMM GUI website (https: / / charmm-gui.org / ), and the polymer brush coating model was constructed through VMD software, and the polymer brush coating model was obtained after solvation treatment. In the polymer brush coating model, the distances between polymer chains were 2nm, 1.5nm, and 1.2nm, respectively, forming polymer brush coatings with three grafting densities. The model size was controlled to be 8nm, so the polymer brush coating models with different grafting densities contained 9, 16, and 25 polymer brush coating chains, respectively. In the subsequent introduction, low, medium, and high represent the polymer brush coating models with three grafting densities.

[0051] The simulation parameters of the above models were set respectively. The three boundaries of the simulation system X, Y, and Z were set as periodic boundaries, and the cutoff distance of the short-range Lennard-Jones interaction was set as The time step is 2 fs. Energy minimization is performed for 50,000 steps to eliminate bad contacts and reduce the system energy. The relaxation time is 2 ns.

[0052] The above models were simulated and calculated respectively. The MD method is mainly based on the classical Newtonian mechanics to simulate the movement and distribution of atoms in the calculation system, that is, the distance between atoms and the potential energy function determine the force between atoms, which in turn leads to the movement and redistribution of atoms. The position and velocity information of each atom at each simulation moment are recorded, and the cycle is repeated until the atomic trajectory information of long-term simulation under certain conditions is obtained. The simulation time is 32ns.

[0053] Data analysis, based on the atomic velocity and position information obtained by calculation, analyzes the structural parameters of the object system, focusing on the association between polymer brush coating chains and the mobility information of polymer chains. In order to realize the interchain association of polymer brush coating, the distance between the carbon atom on the quaternary amino group of the zwitterionic monomer and the oxygen atom on the anionic group is statistically used to represent the interchain association of polymer brush coating. By comparison, it can be found that with the increase of grafting density, the interchain association rate of PCBMA zwitterionic polymer brush coating increases significantly, such as Figure 7 shown.

[0054] Preferably, in step 4, the simulation data in step 3 are extracted and analyzed. In order to quantitatively characterize the mobility of the zwitterionic polymer brush coating chain, the position distribution of the center of mass of the top zwitterionic monomer of the polymer brush coating chain on the XY cross section during the statistical simulation process can characterize the mobility of the polymer brush coating chain. By comparison, it is found that as the grafting density increases, the mobility of the PCBMA polymer brush coating chain decreases, such as Figure 8 shown.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings, characterized in that: The steps include: Construct a zwitterionic polymer brush coating model and set up the model; The MD method is used to simulate and calculate the atomic motion and distribution in the zwitterionic polymer brush coating model, and the position and velocity information of each atom at each simulation moment is recorded until the atomic trajectory information of long-term simulation under set conditions is obtained; According to the atomic velocity and position information obtained by calculation, the structural parameters of the zwitterionic polymer brush coating model are analyzed and obtained, including the association between the chains of the zwitterionic polymer brush coating and the mobility information of the polymer chain; The substrate of the zwitterionic polymer brush coating model is a silicon substrate, and a segment of the zwitterionic polymer is fixed on the silicon substrate and arranged perpendicularly to the silicon substrate; The length of the zwitterionic polymer chain can be controlled to simulate the effect of zwitterionic polymer brush coating thickness on the interchain association and mobility of polymer brush coating chains; The distance between zwitterionic polymer chains can be controlled to simulate the effect of zwitterionic polymer brush coating grafting density on the interchain association and mobility of polymer brush coating chains; When setting up the model, the X, Y, and Z boundaries of the simulation system are all set to periodic boundaries, and the cutoff distance of the short-range Lennard-Jones interaction is set to The time step is 2fs; the energy minimization is performed for 50,000 steps to eliminate poor contact and reduce the system energy; the relaxation time is not less than 2ns; when the MD method is used to simulate the atomic motion and distribution in the zwitterionic polymer brush coating model, the simulation time is not less than 30ns; When conducting the analysis, the distance between the carbon atom on the quaternary amino group of the zwitterionic polymer monomer and the oxygen atom on the anionic group is counted to characterize the interchain association of the zwitterionic polymer in the zwitterionic polymer brush coating; When the distance between the carbon atom on the quaternary amino group of the zwitterionic polymer monomer and the oxygen atom on the anionic group is smaller than the distance between the carbon atom on the quaternary amino group and the oxygen atom on the anionic group of the same zwitterionic monomer, interchain association occurs; During the analysis, the position distribution of the center of mass of the top zwitterionic monomer of the zwitterionic polymer chain in the zwitterionic polymer brush coating on the XY cross section is statistically simulated to characterize the mobility of the polymer brush coating chain; a circular area covers 90% of the distribution points on the XY plane, and the radius of the circle is defined as the distribution radius. The larger the distribution radius, the higher the mobility.

2. The method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings according to claim 1, characterized in that: When constructing the zwitterionic polymer brush coating model, the molecular model of the zwitterionic polymer brush coating material was drawn using Materials Studio software, and the structure was optimized to obtain the CHARMM force field potential energy parameters of the zwitterionic polymer brush coating material. The zwitterionic polymer brush coating model was constructed using VMD software and solvation treatment was performed.

3. The method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings according to claim 1, characterized in that: The material of zwitterionic polymer brush coating is phosphorylcholine, carboxybetaine or phosphorylcholine.

4. The method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings according to claim 2, characterized in that: During the solvation treatment, ions are added to the solution environment, and the ions are selected from chloride ions, sodium ions, calcium ions, magnesium ions or sulfate ions.

5. The method for simulating and quantifying the interchain association and chain mobility of zwitterionic polymer brush coatings according to claim 1, characterized in that: The parameters for model setting include boundary conditions of the calculation system, potential function selection, energy minimization, relaxation balance and output parameters.

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