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通过分子动力学模拟对聚酰亚胺/铜纳米颗粒复合物的形态结构、 热力学性质、力学特性进行计算, 分析其随模拟温度和纳米颗粒尺寸的变化规律. 模拟结果表明, 聚酰亚胺/铜纳米颗粒复合物为各向同性的无定形态结构, 铜纳米颗粒与聚酰亚胺基体之间通过较强的范德华作用结合在一起使结构更加稳定, 铜纳米颗粒表面多个原子层呈现无定形状态, 在铜颗粒和聚酰亚胺基体之间形成界面层, 界面区域随颗粒尺寸和温度的增加分别减小和增加. 聚酰亚胺/铜纳米颗粒复合物的等容热容随着颗粒尺寸增大而明显增高, 随温度变化比聚酰亚胺体系更为缓慢, 在较低温度下较小颗粒尺寸复合物的热容比聚酰亚胺体系更低. 聚酰亚胺/铜纳米颗粒复合物的热压力系数随颗粒尺寸增加而显著增大, 比聚酰亚胺体系的热压力系数更小, 且随温度升高而减小的程度要小得多. 聚酰亚胺/铜纳米颗粒复合物的热力学性质表现出明显的尺度效应, 温度稳定性明显高于聚酰亚胺体系. 聚酰亚胺/铜纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量, 具有比聚酰亚胺体系更低的杨氏模量和泊松比, 随温度升高分别减小和增大, 与聚酰亚胺体系随温度的变化趋势相反, 且杨氏模量的温度稳定性显著提高, 同时泊松比随纳米颗粒尺寸增大而减小, 具有明显的尺度效应. 加入铜纳米颗粒形成复合物可获得与聚酰亚胺体系显著不同的力学新特性.Molecular dynamics simulations of polyimide/copper-nanoparticle composites are implemented to calculate the morphological structures, thermodynamic and mechanical properties, and to investigate their relationships with the nanoparticle dimension and simulation temperature. The results demonstrate that polyimide/copper-nanoparticle composites are of isotropic amorphous structures, in which the copper nanoparticles combine with polyimide matrix due to van der Waals effect and multi-layers of atoms on nanoparticle surface change into amorphous configurations, forming interface layers between them. The interface regions shrink and expand respectively with increased nanoparticle dimension and temperature. The polyimide/copper-nanoparticle composites exhibit the explicit increase of isometric heat capacity with larger nanoparticle dimension in moderated temperature dependence, resulting in lower heat capacities at relatively low temperature for nanocomposites with relatively small nanoparticle size, compared with polyimide system. The thermal pressure coefficients of polyimide/copper-nanoparticle composites are distinctly higher than those of polyimide system, and increase substantially with enlarged nanoparticle dimension and reduce slightly with elevated temperature. The thermodynamic properties of polyimide/copper-nanoparticle composites manifest obvious scale-effect and distinctly higher temperature stability than polyimide system. The mechanical properties of polyimide/copper-nanoparticle composites represent isotropic elastic constant tensors with distinctly lower Young modulus and Poisson ratio than those of polyimide system, which decrease and increase respectively with increasing simulation temperature, exactly contrary to polyimide system and with substantially higher temperature stability of Young modulus. The composites with larger nanoparticle dimension exhibit considerably higher Poisson ratio with slight change of Young modulus, indicating the remarkably different mechanical properties of new nanocomposites with Cu nanoparticle filler.
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