CN119560035B

CN119560035B - Modeling Methods for Dissipative Particle Dynamics Studies of Ternary Entangled Polymer Mixtures of Homopolymer-Homopolymer-Diblock Copolymer

Info

Publication number: CN119560035B
Application number: CN202311122394.3A
Authority: CN
Inventors: 李叶迪; 王凡; 郭洪霞
Original assignee: Institute of Chemistry CAS
Current assignee: Institute of Chemistry CAS
Priority date: 2023-09-01
Filing date: 2023-09-01
Publication date: 2025-10-31
Anticipated expiration: 2043-09-01
Also published as: CN119560035A

Abstract

The invention discloses a construction method for realizing a ternary entanglement polymer mixture of a homopolymer and a diblock copolymer by adopting a dissipative particle dynamics method. The method comprises the steps of obtaining the characteristic ratio and balance bond length of a simulation system, generating a series of homopolymers and diblock copolymers taking the bond length as a step length, putting the obtained series of random walking homopolymers and copolymers into a simulation box according to the chain length, the chain number and the number density of the simulation system, introducing interaction potential among particles, introducing bond-forming interaction potential by using simple harmonic spring potential, introducing bond angle interaction potential by using a bending potential function, gradually increasing rejection parameters, keeping the rejection parameter difference among each stage equal or approximately equal, setting the rejection parameters as end use values, and detecting whether the conformation of a chain is balanced. The ternary entangled polymer mixture constructed by the invention can accurately describe the dynamics and rheological properties of the entangled polymer blend and can be used for researching the structure and rheological properties of the entangled polymer interface.

Description

Model construction method for researching homopolymer-diblock copolymer ternary entanglement polymer mixture by dissipative particle dynamics

Technical Field

The invention relates to a model construction method for researching a homopolymer-diblock copolymer ternary entanglement polymer mixture by dissipative particle dynamics, and belongs to the field of computer simulation.

Background

The polymer blend with different chemical properties is an effective method for manufacturing new materials, but the incompatibility among different polymers can cause the phase separation of the blend, and then the polymer-polymer interface with weaker adhesive force and mechanical property can be generated inside the material. The rheological and molecular chain dynamics behavior of incompatible blends can be very complex due to the presence of interfaces, especially when entanglement topology constraints are present at the interfaces, and thus entangled polymer-polymer interfaces become a hotspot of interest to material scientists. In order to enhance the strength of the interface, additives such as block copolymers are usually added at the interface. The block copolymer exceeding the entanglement length not only plays roles of reducing interfacial tension and increasing interfacial viscosity, but also can further perfect the entanglement network of the interface and inhibit the generation of interfacial velocity slip. Therefore, the ternary polymer blend has great industrial application value and complex interface property.

Despite the experimental findings of the rheological behavior of the polymer-polymer interface in the abundant ternary polymer blends over the last decade, the explanation at the molecular level remains relatively poor. On the other hand, it is very difficult and time consuming to obtain balanced, homo-block copolymer ternary entangled polymer mixtures with a flat interface by means of phase separation kinetics. Recently Nikunen et al improved the traditional dissipative particle dynamics approach, namely increasing the conservation force from 25 to 200 to create entanglement effects. Moreover, researchers have demonstrated that this process has a shorter entanglement length than the Kremer-Grest model, and thus the model can simulate a polymer with a greater entanglement number with the same chain length. Accordingly, the present invention contemplates providing a model building method for dissipative particle dynamics studies of a homopolymer-diblock copolymer ternary entangled polymer blend system to study the nature and rheological behavior of the entangled polymer-polymer interface therein.

Disclosure of Invention

The invention aims to provide a construction method for researching a homopolymer-diblock copolymer ternary entanglement polymer mixture by adopting dissipative particle dynamics,

The invention provides a construction method for realizing a ternary entanglement polymer mixture of a homopolymer-diblock copolymer by adopting a dissipative particle dynamics method, which comprises the following steps:

S1, obtaining a characteristic ratio and a balance bond length of a simulation system, and generating a series of homopolymers and diblock copolymers taking the bond length as a step length according to the balance bond length and the characteristic ratio, so that the generated chain has a correct end distance on a large scale;

S2, putting a series of random walking homopolymers and copolymers obtained in the step S1 into a simulation box according to the chain length, the chain number and the number density of the simulation system;

S3, introducing interaction potential among particles by adopting a dissipative particle dynamics method, introducing bond-forming interaction potential by using a simple harmonic spring potential, and introducing bond angle interaction potential by using a bending potential function;

S4, gradually increasing rejection parameters, wherein the rejection parameter difference between each two phases is equal or approximately equal, and the rejection parameter increasing values of different particles are equal;

s5, setting the rejection parameter as a final use value, and running for 1-2 rouse time;

and S6, detecting whether the conformation of the chain is balanced, if the distance in the mean square chain of each component is not changed with time, balancing the system, otherwise, not balancing the system, and repeating the step S5 to obtain a balanced system.

In the above construction method, in step S1, if the feature ratio is known, it may be directly used, or if the feature ratio of the polymer is unknown, it may be obtained by directly simulating a short-chain polymer to obtain a balanced bond length, and according to a bond vector correlation function, a bond angle cosine value is obtained, and then according to a theoretical prediction of a free rotation chain, a theoretical value of the feature ratio is obtained. The aspect ratio and chain length employed to form the initial state of the diblock copolymer are those of a homopolymer having the same chain length as it was.

In the above construction method, in step S2, the simulation box is divided into an upper part and a lower part, and homopolymers a _N、B_N are randomly placed in the upper part and the lower part of the simulation box, so that an interface a _N-B_N is formed in the middle, the upper boundary and the lower boundary of the simulation box, the diblock copolymer is randomly placed in the interface a _N-B_N, and the surface densities of the block copolymers on the two interfaces are kept equal, and the junction point of the two blocks is located on the interface a _N-B_N, namely, the diblock copolymer is determined to be on the interface.

In the above construction method, in step S3, in the dissipative particle dynamics method, in order to separate particles better from each other, the repulsive parameter of the conservative force between the same kind of particles or between the affinity particles is 25, that is, a _AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD =25, the repulsive parameter between different copolymer particles is a _AB =55, the repulsive parameter between the non-affinity block copolymer and the homopolymer particles is a _BC＝a_AD =40 to 55, and in addition, the bonding potential coefficient is always twice the repulsive parameter between the same kind of particles.

In the above construction method, in step S3, in the dissipative particle dynamics method, the simulated time is 1-2 Rouse times, and the Rouse time is Rouse relaxation time of the homopolymer with the same chain length corresponding to the polymer with the longest chain length in the system.

In the above construction method, in step S4, the running time is 1 to 2rouse time.

In the above construction method, in step S5, the rejection parameter is 200, i.e a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝200,a_AB＝230,a_BC＝a_AD＝215～230.

The ternary entangled polymer mixture melt with balanced conformation obtained by the steps can qualitatively describe the structure, dynamics and rheological properties of the polymer mixture, especially the structure and rheological properties of an interface, so that the experimental phenomenon can be explained in a molecular level, and a more accurate related theory can be established.

The balance system obtained by constructing the model by the method also belongs to the protection scope of the invention.

The invention has the following beneficial effects:

By the construction method, the ternary entangled polymer mixture with entangled interface and close to equilibrium conformation is established, homopolymer and copolymer molecules are put into a preset phase region and corresponding repulsive parameters are adjusted to quickly obtain the equilibrium conformation of the entangled polymer mixture, compared with the method for obtaining the phase-separated entangled polymer mixture directly through phase separation dynamics, the method has the advantages that the used balance time is shorter, a large amount of time and calculation resources are saved, and an effective way is provided for efficiently and accurately researching the structure and property relation of the entangled polymer mixture and an entangled interface thereof.

Drawings

FIG. 1 shows a model of a homopolymer (A _N、B_N), a diblock copolymer (C _ND_N) employed in the present invention.

Figure 2 shows a model of dissipative particle dynamics for a homopolymer-diblock copolymer ternary entanglement polymer blend system constructed in accordance with the present invention.

Fig. 3 shows the change in total particle count and entanglement point density along the interface normal direction.

Fig. 4 shows the displacement of the interfacial block copolymer in the flow field velocity direction and velocity gradient direction over time under shear flow.

Fig. 5 shows a cross-section of the velocity of particles under shear flow along the normal direction of the interface.

Detailed Description

The experimental methods used in the following examples are conventional methods unless otherwise specified.

Materials, reagents and the like used in the examples described below are commercially available unless otherwise specified.

The specific implementation of the balancing method of the present invention will be described by taking the balancing of a ternary entangled polymeric mixture of homopolymer A ₁₂₅ -homopolymer B ₁₂₅ -diblock copolymer C ₁₂₅D₁₂₅ as an example:

1) The homopolymer system with chain length of 10, chain number of 10 and number density of 1 was directly simulated by entanglement dissipative particle dynamics to obtain a balance bond length of 0.964. Obtaining a key angle cosine value when a bending potential coefficient is 2 according to a potential function in a bending potential cosine form, and substituting the key angle cosine value into an intra-chain distance formula of a free rotating chain FRC model to obtain a characteristic ratio of 3.32, setting a balance key length of an initial conformation to be 0.95, and generating a series of homopolymers and diblock copolymers with approximately correct end distances on a large scale by random walking according to the relation between the end distances of the free rotating chains and the characteristic ratio;

2) Setting the bulk coefficient density to be 1, setting the chain length of the homopolymer A ₁₂₅、B₁₂₅ to be 125, the chain number to be 1440, setting the length of each block of the diblock copolymer C ₁₂₅D₁₂₅ to be 125, the total chain length to be 250, the chain number to be 160, setting the size of a simulation box to be 80r _c×50r_c×100r_c, equally dividing the box into an upper part and a lower part along the z direction, randomly putting the homopolymer A ₁₂₅、B₁₂₅ generated in the step (1) into the upper part and the lower part of the box respectively, generating an A ₁₂₅-B₁₂₅ interface at the positions of z=50r _c and z=0 (or 100r _c), and then respectively placing 80 diblock copolymers C ₁₂₅D₁₂₅ on the interfaces of z=50r _c and z=0, namely, the connection points of the blocks C ₁₂₅ and D ₁₂₅ are positioned at the positions of z=50r _c and z=0;

3) Introducing inter-particle interaction potential by adopting a dissipative particle dynamics method, wherein the repulsive parameter is a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝25,a_AB＝55,a_BC＝a_AD＝55,, a bond-forming interaction potential is introduced by using a simple harmonic spring potential, a bond angle potential is introduced by using a cosine form bending potential, and a Rouse time is simulated;

4) Every Rouse time, the repulsive parameters are respectively adjusted to a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝50,a_aB＝80,a_BC＝a_AD＝80、a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝100,a_AB＝130,a_BC＝a_AD＝130 and a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝150,a_AB＝180,a_BC＝a_AD＝180,, and the bonding potential coefficients are always twice as high as those of the same particle repulsive parameters;

5) Setting the rejection parameter as an end-use value, namely, running the rejection parameter for Rouse time at a_AA＝a_BB＝a_CC＝a_DD＝a_AC＝a_BD＝200,a_AB＝230,a_BC＝a_AD＝230,, and respectively representing the chain conformations of A ₁₂₅、B₁₂₅ and C ₁₂₅D₁₂₅ in the system, namely, the intra-chain distance;

6) And (5) repeating the step (5) until the intra-chain distance is not changed any more, and obtaining an initial state with good conformational balance, as shown in figure 2.

The system established as described above was analyzed. First, the particle density and normalized entanglement density were counted and distributed along the normal direction of the interface (fig. 3), and the decrease in the particle density and entanglement density at the interface was found to indicate that the intermolecular chain interactions at the interface were weaker than those at the bulk. If a shear flow with a velocity gradient perpendicular to the interface is applied to the system in a direction parallel to the interface, the displacement of the block copolymer in all directions is counted (figure 4), and the displacement of the molecular chain in the direction of the velocity gradient of the flow field is found to be almost negligible compared with the direction of the velocity of the flow field, which means that the block copolymer is fixed on the interface and cannot move along the normal direction of the interface. Counting the velocities of all particles in the direction of the shear field, a discontinuous change in velocity at the interface (fig. 5), i.e. a phenomenon of velocity slip, is observed, which is caused by weak inter-chain interactions of molecules at the interface.

In conclusion, the ternary entangled polymer mixture melt with balanced conformation constructed by the invention can qualitatively describe the structure, dynamics and rheological properties of the polymer mixture, especially the structure and rheological properties of an interface, so that the experimental phenomenon can be explained in a molecular level, and a more accurate related theory can be established.

Claims

1. A method for constructing a ternary entangled polymer mixture of homopolymer-homogene-diblock copolymer using dissipative particle dynamics, comprising the following steps:

S1. Obtain the characteristic ratio and equilibrium bond length of the simulation system. Based on the equilibrium bond length and the characteristic ratio, generate a series of homopolymers and diblock copolymers with bond length as the step size, so that the generated chains have the correct end distance on a large scale.

S2. Based on the chain length, chain number, and number density of the simulation system, place the series of random walk homopolymers and copolymers obtained in step S1 into the simulation box;

The simulation box is divided into an upper part and a lower part, and homopolymers _AN and _BN are randomly placed in the upper part and the lower part of the simulation box, respectively. Thus, _AN- _BN interfaces are formed in the middle, upper boundary and lower boundary of the simulation box, respectively. The diblock copolymer is randomly placed in the _AN - _BN interface and the areal density of the block copolymer on the two interfaces is kept equal.

S3. Use dissipative particle dynamics to introduce interaction potentials between particles, use simple harmonic spring potentials to introduce bonding interaction potentials, and use bending potential functions to introduce bond angle interaction potentials.

S4. Gradually increase the repulsion parameter, and keep the difference in repulsion parameter between each stage equal, and keep the increase in repulsion parameter for different particles equal;

S5. Set the rejection parameter to the final usage value and run for 1~2 Rouse times;

S6. Check if the conformation of the chain is in equilibrium. If the mean square intrachain distance of each component no longer changes with time, the system has reached equilibrium. Otherwise, the system has not reached equilibrium. Repeat step S5 to obtain an equilibrium system.

2. The construction method according to claim 1, characterized in that: in step S3, in the dissipative particle dynamics method, the repulsion parameter of the conservative force between like particles or between particles with affinity is 25, i.e. The repulsion parameter between different copolymer particles is The repulsion parameter between the incompatible block copolymer and the homopolymer particles is: = .

3. The construction method according to claim 2, characterized in that: in step S3, the simulation time in the dissipative particle dynamics method is 1 to 2 Rouse times.

4. The construction method according to any one of claims 1-3, characterized in that: in step S4, the running time is 1~2 Rouse time.

5. The construction method according to any one of claims 1-3, characterized in that: in step S5, the rejection parameter is 200.

6. The initial equilibrium state of the coarse-grained ternary entangled polymer mixture constructed by the method of any one of claims 1-5.