Study on molecular dynamics simulation for evolution of macromolecular structure during shear deformation of polyvinylidene fluoride

doi:10.19491/j.issn.1001-9278.2025.07.011

Abstract

Abstract:

This study employed molecular dynamics simulations to investigate the microstructural evolution of polyvinylidene fluoride （PVDF） during shear deformation. The effects of chain length， mixed polymerization degree， and shear strain rate on the shear behavior of PVDF were systematically examined， with analysis focusing on stress⁃strain response， end⁃to⁃end distance， mean square displacement， and radial distribution function. Results revealed that the shear deformation process exhibited three distinct stages： elastic deformation， stress yield， and stress softening. Longer polymer chains demonstrated greater resistance to unwinding， requiring higher shear stresses and exhibiting more pronounced changes in end⁃to⁃end distance. For systems with mixed polymerization degrees， the shear response was predominantly governed by long⁃chain molecules， leading to increased shear modulus and chain⁃length⁃dependent variations in end⁃to⁃end distance. Furthermore， higher strain rates necessitated greater shear stresses， induced larger changes in molecular conformation， and impeded chain unwinding. These findings provide molecular⁃level insights into the shear⁃induced structural evolution of PVDF， offering valuable guidance for optimizing its processing and performance.

Key words: polyvinylidene fluoride, shear deformation, microstructural evolution, molecular dynamics simulation

CLC Number:

TQ325.407

SUN Yueying, TANG Xiaolong, ZOU Zhongyi, WANG Mengqiao, LIU Jitao. Study on molecular dynamics simulation for evolution of macromolecular structure during shear deformation of polyvinylidene fluoride[J]. China Plastics, 2025, 39(7): 63-71.

Figures/Tables 20

Fig.1. Repetitive units of PVDF， molecular chains of PVDF， and amorphous unit cell snapshots of PVDF

分组	晶胞构成	原子总数
100/20	聚合度为100，20条	12 040
200/10	聚合度为200，10条	12 020
400/5	聚合度为400，5条	12 010
混合聚合度	聚合度为100，2条	12 018
	聚合度为200，5条
	聚合度为400，2条

Tab.1. Molecular chain composition and total number of atoms in different types of PVDF amorphous unit cells

类型	参数
力场	COMPASSII
系综	NVE
时间步长	1 fs
范德华作用	Atom based
截断半径	12.5 Å
静电作用	Ewald加和计算
精度	0.001 kcal/mol
缓冲区宽度	0.5 Å

Tab.2. Parameter Setting for Annealing and Shear Process of PVDF Amorphous Cell

Fig.2. Temperature and energy changes during annealing process

Fig.3. Schematic diagram of cutting process

Fig.4. Simulated snapshots of PVDF amorphous unit cells with different degrees of shear

Fig.5. Simulation snapshot of two molecular chains with different degrees of shear in PVDF amorphous unit cell

Fig.6. Stress⁃strain curve of PVDF amorphous cell during shear deformation process

Fig.7. Schematic diagram of PVDF molecular chain end distance

Fig.8. Variation of End Distance and Average End Distance during PVDF Shear Deformation Process

Fig.9. Mean square displacement of PVDF molecular chains

Fig.10. Comparison of radial distribution functions between initial and final states during PVDF shear deformation process

Fig.11. Stress⁃strain and shear modulus diagrams of PVDF with different chain lengths during shear deformation process

Fig.12. Average End Distance Variation during PVDF Shear Process

Fig.13. Stress⁃strain diagram of shear deformation process of PVDF unit cell with mixed polymerization degree

Fig.14. The average end distance variation during the shear deformation process of PVDF with mixed polymerization degree

剪切应变速率/ps^-1	剪切时间/ps	应变
0.05	300	15
0.5	30	15
5	3	15

Tab.3. Shear time corresponding to different shear strain rates

Fig.15. Stress strain and shear modulus diagrams of PVDF during shear deformation at different shear strain rates

Fig.16. Average end distance variation of PVDF shear at different strain rates

Fig.17. Snapshot of the final state of PVDF unit cells sheared at different strain rates

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