Mechanical behavior and modification of poly-ether-ether-ketone using a molecular dynamics method
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摘要: 采用分子动力学方法预测聚醚醚酮（PEEK）的拉伸力学性能，对PEEK分子模型进行各向异性控压的非平衡态拉伸模拟，获得PEEK材料的应力-应变曲线，计算弹性模量、屈服强度等力学性能。分析不同应变率和温度下PEEK的力学性能、自由体积、均方回转半径和体系能量随拉伸应变的变化规律，进而解释PEEK分子链特征与材料宏观性能的关系。结果表明：随着应变率的增加，PEEK的弹性模量和屈服强度大幅提高；随着温度的增加，PEEK的弹性模量和屈服强度大幅降低；在拉伸弹性和屈服阶段体系的自由体积增加较快，分子链的均方回转半径基本不变，体系总势能以非键能为主。非键相互作用是影响PEEK弹性模量和屈服强度的一个主导因素，由此提出氨基修饰PEEK侧链的改性策略，结果表明，氨基官能化PEEK的弹性模量和屈服强度较PEEK分别提升21%和34%。Abstract: The molecular dynamics method was employed to predict the tensile mechanical properties of polyether-ether-ketone (PEEK). Non-equilibrium tensile simulation with anisotropic pressure control was employed to obtain the stress-strain curve of PEEK, and to calculate the elastic modulus, yield strength and other mechanical properties. The influences of the strain rate and temperature on the mechanical properties, free volume, mean square radius of gyration (Rg), and energy for PEEK were investigated to explain the relationship between PEEK chain characteristics and macro mechanical properties. The results indicate that the elastic modulus and yield strength of PEEK significantly increase with the increase of strain rate, and significantly decrease with the increase of temperature. In the elastic and yield stage, free volume linearly increases, and Rg of PEEK chains remains steady, and the non-bonded energy results in the amount of the total potential energy increase. The interchain non-bonded interactions play a dominant role in the elastic and yield performance. Therefore, the amino modification strategy is investigated to improve the mechanical property of PEEK. It is found that the elastic modulus and yield strength of PEEK modified by amino are increased by 21% and 34% respectively than that of PEEK.
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图 1 聚合物分子结构和拉伸变形示意图 （a）PEEK；（b）PEEK-NH2；（c）拉伸变形
Figure 1. Molecular structures of polymers and schematic diagram of tensile deformation （a）PEEK；（b）PEEK-NH2； （c）tensile deformation.
图 2 基于分子模拟的PEEK应力-应变曲线（a）和拉伸过程中的PEEK分子构型，相同颜色原子在同一条分子链（b）
Figure 2. Stress-strain curves of PEEK through molecular dynamics (a) and molecular configuration of PEEK during tensile deformation（atoms with the same color are on the same molecular chain）(b)
图 3 PEEK体系在不同应变率下的应力-应变曲线
Figure 3. Stress-strain curves of PEEK system at different strain rates
图 4 PEEK体系在不同应变率下拉伸过程 （a）自由体积；（b）均方回转半径
Figure 4. Curves of free volume and mean square radius of gyration vs strain for PEEK at different strain rates (a) free volume；（b）mean square radius of gyration
图 5 不同应变率下PEEK体系拉伸过程的键合能、非键能和总势能随应变变化曲线 （a）0.1 ns–1；（b）1 ns–1；（c）10 ns–1
Figure 5. Curves of bonded energy, non-bonded energy and total potential energy vs strain for PEEK system at different strain rates (a) 0.1 ns–1；(b) 1 ns–1； (c) 10 ns–1
图 6 不同温度下PEEK聚合物的应力-应变曲线
Figure 6. Stress-strain curves of PEEK polymer at different temperatures
图 7 不同温度下PEEK体系 （a）自由体积与拉伸应变的关系；（b）分子链均方回转半径与拉伸应变的关系
Figure 7. Curves of PEEK system at different temperatures （a） free volume vs strain；（b） mean square radius of gyration vs strain
图 8 在不同温度下PEEK体系能量随拉伸应变的变化 （a）键合能；（b）非键能；（c）总势能
Figure 8. Energy as a function of tensile strain for PEEK system at different temperatures (a) bonded energy； (b) non-bonded energy； (c) total potential energy
图 9 PEEK和PEEK-NH2在0.1 ns–1应变率下的应力-应变曲线
Figure 9. Stress-strain curves of PEEK and PEEK-NH2 at a strain rate of 0.1 ns–1
图 11 PEEK和PEEK-NH2体系 （a）相对自由体积与应变的关系；（b）均方回转半径与应变的关系
Figure 11. Curves of PEEK and PEEK-NH2 (a) relative free volume vs stain； (b) mean square radius of gyration vs stain
图 12 键合能、非键能和总势能随应变变化曲线 （a）PEEK；（b）PEEK-NH2
Figure 12. Bonded energy, non-bonded energy and total potential energy as a function of strain (a) PEEK ； (b) PEEK-NH2
表 1 PEEK体系在不同应变率下的力学性能
Table 1. Mechanical properties of PEEK system at different strain rates
Strain rate /ns–1 Elastic modulus /GPa Yield strength /MPa 0.1 3.87±0.30 157.3±10.1 1 4.01±0.43 198.6±8.7 10 5.02±0.70 253.3±29.0 
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表 2 PEEK体系应变为0.5时在不同应变率下的键合能、非键能和总势能
Table 2. Bonded energy, non-bonded energy and total potential energy of PEEK system at a strain of 0.5 and different strain rates
Strain rate/
ns–1Bonded energy/
(kJ·mol–1)Non-bonded energy/
(kJ·mol–1)Total potential energy/
(kJ·mol–1)0.1 2951.77 3505.37 6457.14 1 3628.72 6356.47 9985.20 10 3814.89 10484.79 14299.68
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表 3 不同温度下PEEK聚合物的力学性能
Table 3. Mechanical properties of PEEK polymer at different temperatures
Temperature /K Elastic modulus /GPa Yield strength /MPa 77 6.17±0.51 311.0±2.0 300 3.87±0.30 157.3±10.1 373 2.48±0.48 134.7±7.4 473 1.28±0.30 81.2±0.8
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表 4 PEEK和PEEK-NH2在0.1 ns–1应变率下的力学性能
Table 4. Mechanical properties of PEEK and PEEK-NH2 at a strain rate of 0.1 ns–1
Material Elastic modulus/GPa Yield strength/MPa PEEK 3.87±0.30 157.3±10.1 PEEK-NH2 4.69±1.10 210.2±10.5
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表 5 PEEK和PEEK-NH2在应变为0.5时的键合能、非键能和总势能
Table 5. Bonded energy, non-bonded energy and total potential energy for PEEK and PEEK-NH2 at a strain of 0.5
Material Boned energy/(kJ·mol–1) Non-bonded energy/(kJ·mol–1) Total potential energy/(kJ·mol–1) PEEK 2951.77 3505.37 6457.14 PEEK-NH2 3840.83 6492.42 10333.25
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