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Simulating molecular structures and dynamic behaviors presents critical insights into the microscopic mechanisms governing variations in charge transport properties. In this work, molecular dynamics (MD) simulations integrated with the Compass II force field and molecular modeling (including geometry optimization, annealing, and dynamic equilibration) are conducted to systematically analyze intermolecular interaction energy, free volume distribution, electronic density of states (DOS), charge differential density, and trap energy levels. aiming to unravel the regulatory role of hydrogen bonds in the structural evolution and charge transport dynamics of polypropylene (PP)/polyvinylidene fluoride (PVDF) composite systems. A quantitative framework is further established to correlate hydrogen bond density with key material performance metrics, such as free volume fraction, bandgap energy, and trap energy depth, thereby elucidating the hydrogen bond-mediated modulation of molecular architecture and charge transport behavior in PP/PVDF composites. Simulation results reveal a pronounced dependence of hydrogen bond formation on maleic acid (MA) grafting content. When the mass fraction of MA is 36.22%, the number of hydrogen bonds reaches a maximum value of 20, the intermolecular interaction energy increases to 2171.63 kcal·mol–1, and the free volume fraction reaches a minimum value of 16.03%. At this point, the internal structure of the molecule is most compact. When the mass fraction of MA increases to 52.97%, the band gap of the composite material reaches a minimum value of 3.13 eV, and the depth of the trap energy levels also reaches a maximum value of 3.06 eV. Spatial charge differential density analysis demonstrates that the enhanced electron density is localized near hydrogen-bonded region, thus suppressing electron escape probability by over 40% compared with the scenario in the non-bonded domains. All of the findings highlight a dual mechanism: hydrogen bonds not only reconfigure the molecular topology but also reshape the localized charge distribution, directly suppressing the carrier mobility and changing the charge transport pathways. These findings also establish a robust structure-property relationship, showing that hydrogen bond engineering serves as a pivotal strategy to tailor dielectric performance in polymer composites. By optimizing hydrogen bond density, the trade-off between structural compactness and electronic confinement can be strategically balanced, thus enabling the designing of PP-based dielectrics with low carbon footprints and superior insulating properties. This mechanistic understanding provides actionable guidelines for advancing high-performance insulating materials in energy storage systems, aerospace components, and next-generation electrical devices, where precise control over charge transport is paramount.
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Keywords:
- polypropylene /
- hydrogen bond /
- molecular dynamics /
- charge transport
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图 1 PP/PVDF复合材料空间结构 (a) PP; (b) PVDF; (c) PP-g-MA; (d) PP/PVDF
Figure 1. Spacial structure of PP/PVDF composites: (a) PP; (b) PVDF; (c) PP-g-MA; (d) PP/PVDF.
图 2 不同PP/PVDF复合材料分子结构模型 (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#
Figure 2. Molecular structure models of different PP/PVDF composites: (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#.
图 3 2#复合材料的能量和温度随时间的变化 (a)能量随时间的变化; (b)温度随时间的变化
Figure 3. Time-dependent energy and temperature variation curves of composite 2# in the PP/PVDF system: (a) Energy change curve with time; (b) temperature curve over time.
图 4 9#复合材料中氢键的位置
Figure 4. Spacial distribution of hydrogen bonds in composite 9#.
图 5 不同PP/PVDF复合材料的氢键数量变化趋势
Figure 5. Variation trend of hydrogen bond number of different PP/PVDF composites.
图 6 不同PP/PVDF复合材料自由体积模型 (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#
Figure 6. Free volume models of different PP/PVDF composites: (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#
图 7 不同PP/PVDF复合材料的自由体积分布变化趋势
Figure 7. Variation trend of free volume distribution of different PP/PVDF composites.
图 8 不同PP/PVDF复合材料的态密度变化趋势
Figure 8. Variation trend of state density of different PP/PVDF composites.
图 9 不同PP/PVDF复合材料电荷差分密度 (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#
Figure 9. Charge differential density of different PP/PVDF composites: (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#; (f) 6#; (g) 7#; (h) 8#; (i) 9#.
图 10 不同PP/PVDF复合材料的陷阱能级变化趋势
Figure 10. Variation trend of trap energy levels of different PP/PVDF composites.
表 1 Compass II力场势能和参数及单位
Table 1. Force field potential energy and parameters in COMPASS II.
Epotential Function form Parameters and units Ebond $ {E_{{\text{bond}}}} = \displaystyle\sum\limits_{{\text{bonds}}} {{k_b}{{(r - {r_0})}^2} + k_b^{(3)}{{(r - {r_0})}^3} + k_b^{(4)}{{(r - {r_0})}^4}} $ kb/(kcal·mol–1·Å–2); r, r0/Å Eangle $ {E_{{\text{angle}}}} = \displaystyle\sum\limits_{{\text{angles}}} {{k_\theta }{{(\theta - {\theta _0})}^2} + k_\theta ^{(3)}{{(\theta - {\theta _0})}^3} + k_\theta ^{(4)}{{(\theta - {\theta _0})}^4}} $ kθ/(kcal·mol–1); θ, θ0/(°) Etorsion $ {E_{{\text{torsion}}}} = \displaystyle\sum\limits_{{\text{torsions}}} {{k_\varphi }(1 + \cos (n} \varphi - {\varphi _0})) $ kφ/(kcal·mol–1); φ, φ0/(°) Eout-of-plane $ {E_{{\text{out}} - {\text{of}} - {\text{plane}}}} = \displaystyle\sum\limits_{{\text{out}} - {\text{of - plane}}} {{k_\omega }{\omega ^2}} $ kω/(kcal·mol–1); ω/(°) Evdw $ {E_{{\text{vdW}}}} = \displaystyle\sum\limits_{i, j} {4\varepsilon \left[ {{{\left( {\frac{\sigma }{{{r_{ij}}}}} \right)}^{12}} - {{\left( {\frac{\sigma }{{{r_{ij}}}}} \right)}^6}} \right]} $ Ε/eV; σ/Å; rij/Å Eelectrostatic $ {E_{{\text{electrostatic}}}} = \displaystyle\sum\limits_{i, j} {\frac{{{q_i}{q_j}}}{{4\pi {\varepsilon _0}{r_{ij}}}}} $ qi, qj/e; rij/Å 
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表 2 不同PP/PVDF复合材料体系模型的编号及其质量分数
Table 2. Designation and mass fraction of different PP/PVDF composites models.
试样编号
PP-g-MA/%PVDF/% MA PP 1# 0 77.94 22.26 2# 2.74 75.52 21.74 3# 5.33 73.41 21.26 4# 10.13 69.57 20.30 5# 14.50 65.94 19.56 6# 18.47 62.83 18.70 7# 22.05 59.84 18.11 8# 36.22 48.51 15.27 9# 52.97 35.34 11.69
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表 3 NPT平衡后不同PP/PVDF复合材料能量和温度的波动范围
Table 3. Fluctuation range of energy and temperature of different PP/PVDF composites after NPT equilibrium.
试样
编号平衡
时间/ps波动/% Temperature EPotential EKinetic ENon-bond ETotal 1# 58.93 3.25 1.56 3.85 4.52 4.11 2# 74.68 2.89 2.56 4.26 1.57 2.10 3# 25.95 4.56 4.56 3.73 2.94 1.61 4# 78.59 1.12 2.76 1.52 4.51 1.52 5# 85.45 2.59 3.81 1.14 1.52 3.20 6# 36.58 3.58 4.19 2.81 2.73 2.17 7# 57.58 1.56 1.25 4.20 2.85 3.96 8# 85.42 3.20 2.48 1.52 4.22 2.57 9# 54.20 2.74 4.21 1.23 2.52 1.85
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表 4 不同PP/PVDF复合材料的能量变化
Table 4. Energy evolution in different PP/PVDF composites.
Enon bond/(kcal·mol–1)
EDiagonal/(kcal·mol–1)EInteraction
/(kcal·mol–1)Etotal
/(kcal·mol–1)Evdw EElectrostatic Ebond Eangle Etorsion 1# 84.65 853.99 214.04 371.93 –721.02 53.49 552.18 2# 85.17 906.80 215.48 398.77 –728.18 63.88 601.15 3# 86.71 977.26 217.09 412.65 –751.63 75.86 654.46 4# 97.89 1083.01 218.45 448.12 –753.56 85.58 723.28 5# 110.28 1205.79 242.31 453.70 –770.93 88.09 828.37 6# 110.97 1332.96 264.16 536.79 –787.47 89.02 898.72 7# 122.93 1462.88 268.80 547.69 –792.07 108.50 1002.49 8# 132.42 2094.95 309.91 689.15 –858.76 127.05 1413.73 9# 55.29 3377.36 402.88 1026.23 –1028.7 74.86 2171.63
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