CN-121983152-A - Linear polymer melt entanglement density regulation and control method based on periodic deformation

CN121983152ACN 121983152 ACN121983152 ACN 121983152ACN-121983152-A

Abstract

The application discloses a linear polymer melt entanglement density regulation method based on periodic deformation, and relates to the technical field of molecular dynamics simulation, wherein the method applies periodic stretching compression deformation circulation to a balanced melt model under topological steady state along a single direction under the condition of constant temperature and constant pressure, and changes the position of topological cross points through relative sliding among chains to realize controllable rearrangement of entanglement networks; and then analyzing and extracting topological parameters under different circulation times by utilizing an original path, establishing a quantitative relation between entanglement density and deformation cycle number, and performing stretching compression deformation circulation according to target periodic deformation times based on the quantitative relation to obtain a linear polymer melt model with required target entanglement density.

Inventors

ZHU CHUNHUA
ZHAO JUNHUA
DONG SHUHONG

Assignees

江南大学

Dates

Publication Date: 20260505
Application Date: 20260116

Claims (10)

1. A method for regulating and controlling the entanglement density of a linear polymer melt based on periodical deformation, characterized in that the method for regulating and controlling the entanglement density of the linear polymer melt comprises the following steps: constructing a linear polymer melt initial model containing a plurality of polymer chains, and performing equilibrium relaxation to obtain an equilibrium melt model with a fully formed topological structure; Applying a plurality of stretching compression deformation cycles with periodic deformation times to the balanced melt model along a preset single-axis direction under the condition of constant temperature and constant pressure, and carrying out original path analysis on the balanced melt model after the stretching compression deformation cycles to obtain entanglement density; Respectively applying stretching compression deformation cycles with different periodic deformation times to the balanced melt model, and establishing a quantitative relation between entanglement density and the periodic deformation times; And determining the target periodic deformation times corresponding to the target entanglement density according to the quantitative relation, applying stretching compression deformation circulation of the target periodic deformation times to the balanced melt model along a preset single-axis direction under the condition of constant temperature and constant pressure, and constructing to obtain the linear polymer melt model with the target entanglement density for molecular dynamics simulation.
2. The method of claim 1, wherein applying each stretch compression set cycle to the balanced melt model along a predetermined uniaxial direction comprises: And increasing the dimension of the balanced melt model in the preset uniaxial direction from the initial length to a preset engineering strain amount through a stretching stage, and recovering the dimension of the balanced melt model to the initial length through a compression stage.
3. A method of controlling the entanglement density of a linear polymer according to claim 2, wherein, The strain quantity in the stretching stage is monotonously changed along with time and keeps continuous deformation in the deformation process, the strain quantity in the compression stage is monotonously changed along with time and keeps continuous deformation in the deformation process, and the strain quantity change rates in the stretching stage and the compression stage are the same.
4. The method of claim 1, wherein the topology parameter after the application of the tension compression set cycle corresponding to the number of periodic set cycles to the balanced melt model is detectably changed from the original topology parameter, and the number of periodic set cycles to which the tension compression set cycle is applied is determined according to the chain length of the polymer chain, the chain flexibility, the size of the balanced melt model, or the simulation condition.
5. The method of claim 1, wherein performing a raw path analysis on the balanced melt model after the stretch compression set cycle to obtain the entanglement density comprises: Position constraints are applied to the chain ends of the polymer chains, the intra-chain interaction parameters are adjusted to allow the chains to shrink themselves, the energy of the balanced melt model is minimized while maintaining inter-chain repulsion, each polymer chain is shrunk to a shortest non-traversable path, the number of entanglements is obtained, and the entanglement density is obtained from the number of entanglements.
6. The method of controlling entanglement density of a linear polymer melt according to claim 5, wherein obtaining entanglement density according to the number of entanglement comprises: According to the number of tangles Calculating the entanglement length , Represents the chain length of a single polymer; According to the length of entanglement Calculating to obtain entanglement density , Representing the total number of coarse particles in the balanced melt model, Representing the volume of the balanced melt model.
7. The method of controlling the entanglement density of a linear polymer according to claim 1, wherein the equilibrium relaxation to obtain an equilibrium melt model with a sufficiently formed topology comprises: And performing energy minimization operation on the linear polymer melt initial model, performing regular relaxation under the constant-volume constant-temperature condition, and performing density adjustment and volume balance under the constant-pressure constant-temperature condition until the chain segment distribution, the density distribution and the end-to-end vector autocorrelation function reach a stable state, so as to obtain the balanced melt model with fully formed topological structure.
8. The method of claim 1, wherein constructing an initial model of a linear polymer melt comprising a plurality of polymer chains comprises: Generating an initial conformation model by adopting at least one of a random walking method, a worm chain model or a high-temperature melting generation mode, and filling the initial conformation model into a preset volume to form a linear polymer melt initial model.
9. The linear polymer melt entanglement density modulation method according to claim 1, wherein said linear polymer melt entanglement density modulation method further comprises: constructing a series of linear polymer melt models with different target entanglement densities and consistent local conformations according to the quantitative relation for analyzing the influence of chain entanglement structures on polymer melt dynamics, rheological property or crystallization behavior, wherein the local conformations comprise chain segment bond angles Distribution and coarse grain Local orientation parameters of (a) Distribution.
10. The method of claim 1, wherein the linear polymer melt model is a full atom molecular dynamics model, a coarse particle size molecular dynamics model, or a combination thereof.

Description

Linear polymer melt entanglement density regulation and control method based on periodic deformation Technical Field The application relates to the technical field of macromolecule physics, computing materials and molecular dynamics simulation, in particular to a linear polymer melt entanglement density regulating and controlling method based on periodic deformation. Background Molecular dynamics simulation is an important calculation method for researching microstructure and dynamic behavior of polymer melt, and information such as chain segment arrangement, limited chain movement degree and interaction among chains can be obtained by constructing a chain model with coarse granularity level and evolving under given temperature and pressure conditions. In polymer melt simulation, chain entanglement is a critical topology formed by inter-chain non-traversable constraints, entanglement density being an important parameter characterizing the degree of chain motion limitation, relaxation characteristics, and macroscopic rheological response. Therefore, the polymer melt models with different entanglement densities are constructed in molecular dynamics simulation, and the method has important significance for developing the research on the influence of chain topology on material performance. In the existing molecular dynamics simulation method, the entanglement structure of the polymer chain is usually naturally formed by depending on the initial configuration and the subsequent relaxation process, and the entanglement density is determined by the chain length, the chain flexibility, the initial filling mode and the relaxation condition, so that the entanglement structure is difficult to directly control in the simulation process. Attempts have been made to influence entanglement by changing chain length, adjusting system density, or applying strong flow fields, but these methods often result in significant changes to the local conformation, local orientation, or inter-chain spacing of the chains, making systems in different entanglement states incapable of maintaining structural comparability. In addition, strong flow fields tend to cause non-negligible orientation effects in the melt, such that the results contain both orientation and topology effects, making it difficult to achieve independent analysis of entanglement factors. Under the conventional molecular dynamics simulation time scale, once the polymer inter-chain topological structure is formed, the long-time relaxation does not change significantly even under the condition of constant temperature and constant pressure, so that the entanglement density is difficult to actively adjust within a computable time by adopting the conventional isothermal relaxation means. In addition, the existing entanglement analysis method is mainly used for extracting topological parameters such as entanglement quantity and entanglement length, but cannot be reversely used for constructing a simulation system with target entanglement density, so that systematic study of the topological parameters on performance in a simulation environment is limited. Disclosure of Invention Aiming at the problems and the technical requirements, the application provides a linear polymer melt entanglement density regulating and controlling method based on periodical deformation, and the technical scheme of the application is as follows: a linear polymer melt entanglement density modulation method based on periodic deformation, the linear polymer melt entanglement density modulation method comprising: constructing a linear polymer melt initial model containing a plurality of polymer chains, and performing equilibrium relaxation to obtain an equilibrium melt model with a fully formed topological structure; Applying a plurality of stretching compression deformation cycles with periodic deformation times to the balanced melt model along a preset single-axis direction under the condition of constant temperature and constant pressure, and carrying out original path analysis on the balanced melt model after the stretching compression deformation cycles to obtain entanglement density; Respectively applying stretching compression deformation cycles with different periodic deformation times to the balanced melt model, and establishing a quantitative relation between entanglement density and the periodic deformation times; And determining the target periodic deformation times corresponding to the target entanglement density according to the quantitative relation, applying a stretching compression deformation cycle of the target periodic deformation times to the balanced melt model along a preset single-axis direction under the condition of constant temperature and constant pressure, and constructing to obtain the linear polymer melt model with the target entanglement density for molecular dynamics simulation. The further technical scheme is that the method for applying each stretching compression deform