聚酰亚胺/钽铌酸钾纳米颗粒复合材料结构与机械性能分子动力学模拟

利用多尺度建模方法构建了聚酰亚胺/钽铌酸钾纳米颗粒复合物模型, 通过分子动力学模拟研究了不同尺寸钽铌酸钾纳米颗粒(5.5, 8.0, 9.4, 10.5, 11.5 Å)对复合材料的结构、弹性模量和相互作用能的影响规律, 并通过计算纳米颗粒表面原子键能和单位表面积原子数目探究了复合物机械性能提高的内部机理. 聚酰亚胺和聚酰亚胺/钽铌酸钾复合材料的杨氏模量分别为2.91和3.17 GPa, 泊松比分别为0.37和0.35, 钽铌酸钾纳米颗粒的引入可以显著改善聚酰亚胺的机械性能. 纳米颗粒表面原子的键能为8.62-54.37 kJ·mol^-1, 表明颗粒与基体主要通过范德华力作用结合且有氢键存在. 计算结果表明, 相同掺杂比例下, 纳米颗粒尺寸越小, 纳米颗粒表面原子数目越大, 颗粒与基体作用更强, 杨氏模量的提高幅度越大, 尺寸效应越显著. 因此, 掺杂小尺寸纳米颗粒是提高聚酰亚胺机械性能的有效途径.

Molecular dynamics simulation study on the structure and mechanical properties of polyimide/KTa0.5Nb0.5O3 nanoparticle composites

The polyimide/potassium tantalite niobate (PI/KTa_0.5Nb_0.5O₃) nanoparticle composite model is established by a multi-scale modeling method. The influences of KTa_0.5Nb_0.5O₃ nanoparticles with different sizes (5.5, 8.0, 9.4, 10.5, 11.5 Å) on the structure, elastic modulus and interaction energy of the polyimidebased nanocomposites are investigated by the molecular dynamics simulation. The cell parameters, cohesive energy density, solubility parameter, Young’s modulus and Poisson’s ratio are calculated. Moreover, the bond energy and the number of atoms per unit surface area of the nanoparticles are analyzed to explore the internal mechanism of mechanical property improvement. The results demonstrate that the density of PI matrix is 1.24-1.35 g/cm³, the cohesive energy density of PI matrix is 2.025×10⁸ J/m³, and the solubility parameter of PI matrix is 1.422×10⁴ (J/m³)^1/2, which are consist with the actual PI parameters. Meanwhile, the Young’s moduli of the PI and PI/KTa_0.5Nb_0.5O₃ composites are respectively 2.914 GPa and 3.169 GPa, and the Poisson’s ratios are respectively 0.370 and 0.353, which illustrate that the mechanical properties of the PI could be significantly improved by introducing the KTa_0.5Nb_0.5O₃ nanoparticles. At the same pressure, the increases of Young’s modulus with temperature are basically the same without and with doping the KTa_0.5Nb_0.5O₃ nanoparticles into the PI matrix; and when the temperatures are different, the standard deviations of elastic moduli of the PI matrix and PI/KTa_0.5Nb_0.5O₃ composite are almost the same. No matter what the pressures and the temperature are, the Young’s modulus of PI/KTa_0.5Nb_0.5O₃ composite is always larger than that of PI matrix. These all indicate that the effect of KTa_0.5Nb_0.5O₃ nanoparticle on elastic modulus has a similar variation rule under the selected pressure and temperature conditions. In addition, the bond energies of particle surface atoms are 8.62-54.37 kJ·mol^-1, which shows that the binding force between particles and the matrix is mainly van der Waals force, and hydrogen bonds exist at the same time. When the doping concentration is fixed, the proportion of nanoparticles surface atoms increases significantly as the size decreases, the interaction between particles and the matrix becomes stronger, the Young’s modulus increases obviously and the size effect is more significant. Therefore, it is confirmed that the doping small size KTa_0.5Nb_0.5O₃ nanoparticles into the polyimide matrix is an effective way to improve the mechanical properties of the composite.