Polymer nanocomposites exhibit a heterogeneous mechanical behavior that is strongly dependent on the interaction between the polymer matrix and the nanofiller. Here, we provide a detailed investigation of the mechanical response of model polymer nanocomposites under deformation, across a range of temperatures, from the glassy regime to the liquid one, via atomistic molecular dynamics simulations. We study the poly(ethylene oxide) matrix with silica nanoparticles (PEO/SiO₂) as a model polymer nanocomposite system with attractive polymer/nanofiller interactions. Probing the properties of polymer chains at the molecular level reveals that the effective mass density of the matrix and interphase regions changes during deformation. This decrease in density is much more pronounced in the glassy state. We focus on factors that govern the mechanical response of PEO/SiO₂ systems by investigating the distribution of the (local) mechanical properties, focusing on the polymer/nanofiller interphase and matrix regions. As expected when heating the system, a decrease in Young’s modulus is observed, accompanied by an increase in Poisson’s ratio. The observed differences regarding the rigidity between the interphase and the matrix region decrease as the temperature rises; at temperatures well above the glass-transition temperature, the rigidity of the interphase approaches the matrix one. To describe the nonlinear viscoelastic behavior of polymer chains, the elastic modulus of the PEO/SiO₂ systems is further calculated as a function of the strain for the entire nanocomposite, as well as the interphase and matrix regions. The elastic modulus drops dramatically with increasing strain for both the matrix and the interphase, especially in the small-deformation regime. We also shed light on characteristic structural and dynamic attributes during deformation. Specifically, we examine the rearrangement behavior as well as the segmental and center-of-mass dynamics of polymer chains during deformation by probing the mobility of polymer chains in both axial and radial motions under deformation. The behavior of the polymer motion in the axial direction is dominated by the deformation, particularly at the interphase, whereas a more pronounced effect of the temperature is observed in the radial directions for both the interphase and matrix regions.

中文翻译：

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通过原子模拟研究聚环氧乙烷/二氧化硅纳米复合材料的机械性能分布：从玻璃态到液态

聚合物纳米复合材料表现出异质机械行为，该行为强烈依赖于聚合物基体和纳米填料之间的相互作用。在这里，我们通过原子分子动力学模拟，对模型聚合物纳米复合材料在变形下、在从玻璃态到液态的一系列温度下的机械响应进行了详细研究。我们研究了具有二氧化硅纳米颗粒（PEO/SiO ₂）的聚环氧乙烷基质作为具有有吸引力的聚合物/纳米填料相互作用的模型聚合物纳米复合材料系统。在分子水平上探讨聚合物链的性质表明，基体和相间区域的有效质量密度在变形过程中发生变化。这种密度的降低在玻璃态下更为明显。我们通过研究（局部）机械性能的分布，重点研究控制 PEO/SiO ₂系统机械响应的因素，重点关注聚合物/纳米填料界面和基体区域。正如预期的那样，当加热系统时，观察到杨氏模量下降，同时泊松比增加。观察到的界面和基体区域之间的刚性差异随着温度的升高而减小；在远高于玻璃化转变温度的温度下，界面相的刚性接近基体刚性。为了描述聚合物链的非线性粘弹性行为，PEO/SiO ₂系统的弹性模量被进一步计算为整个纳米复合材料以及界面和基体区域的应变的函数。随着基体和界面应变的增加，弹性模量急剧下降，特别是在小变形状态下。我们还揭示了变形过程中的特征结构和动态属性。具体来说，我们通过探测变形下聚合物链在轴向和径向运动中的活动性来检查变形过程中聚合物链的重排行为以及链段和质心动力学。聚合物在轴向方向的运动行为主要由变形决定，特别是在相间，而在相间和基体区域的径向方向上观察到更明显的温度影响。