纳米粒子影响高分子基体流变性质的微观机理

Properties of polymer nanocomposites in the linear and nonlinear viscoelastic regions are of considerable interest both from a fundamental and an applied viewpoint. In this project, we propose to investigate rheological properties of polymer nanocomposites both at equilibrium and nonequilibrium with the goal of understanding the effects of nanoparticles on polymers via molecular dynamics simulations. We focus on the microscopic structural and dynamic properties at equilibrium, such as the diffusion behavior of nanoparticles and the changes of entangled networks, which are associated with various rheological behaviors. We consider a variety of deformation conditions including steady shear, oscillatory shear as well as start-up shear. By simulation, we will understand the origins of the increase (decrease) of viscosity due to nanoparticles, reveal the interplay between kinds of nanoparticles and polymer networks, and clarify the relationship between flow-induced nanoparticle dynamics and the deformation, orientation and motion of polymer chains. On the basis of this project, we hope to understand the experimental findings at the molecular level and provide a physical picture for developing the theoretical models and guiding the material designs.

高分子纳米复合物材料的流变性质对材料的生产加工及老化疲劳具有重要实际意义，其微观机理也是高分子科学中尚未解决的重要的基础性科学问题。本项目拟采用计算机模拟方法，针对高分子纳米复合物体系，进行一系列平衡态和启动剪切、振荡剪切及稳态剪切等非平衡态研究，揭示纳米粒子增加（减小）高分子基体粘度的微观机理，明晰不同形状、不同尺寸纳米粒子与高分子网络结构相互作用的微观机制，阐述流场诱导纳米粒子动力学与高分子链拉伸、取向及运动的内在关系。在此基础上，从分子水平上解释实验结果，为建立理论模型提供相应的微观物理图像，为材料性能调控提供依据。

揭示流变行为的微观机理对于高分子纳米复合材料的生产加工具有重要意义。本项目采用分子动力学模拟，分别对当前主流的两类体系----球状纳米粒子/高分子复合体系和棒状纳米粒子/高分子复合体系----开展了平衡态以及一系列启动剪切、振荡剪切及稳态剪切的相关研究。平衡态研究相关研究阐述了纳米粒子对周围分子链结构和动力学行为带来的巨大影响，揭示了纳米粒子改变高分子基体粘度的微观机理。与此同时，我们还明晰了不同尺寸以及浓度条件下纳米粒子与高分子网络相互作用的微观机制。在外场下，我们阐述了流场诱导下纳米粒子动力学与高分子链拉伸、取向及运动的内在关系，揭示了纳米粒子所带来的结构和动力学上的变迁，并且将上述行为与体系的流变行为相关联，在上述研究基础上建立了宏观流变行为的微观物理图像，加深了对于复合体系流变行为的认识水平，并且为进一步指导改进复合材料的加工工艺打好了基础。

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