Nanosize Effects in Mechanical Properties of Nanotube Dispersed Composites

近年来，越来越多的研究已经发表，报告了添加碳纳米管（CNT）的聚合物的机械性能。CNT的添加不一定改善聚合物的机械性能。实验结果的多样性来自于由于CNT的聚集和利用不同的试样几何形状而产生的缺陷，除了取决于聚合物的种类和CNT的表面状态的CNT/聚合物相互作用的差异之外。在本研究中，时间分辨小角X射线散射测量已进行使用同步辐射过程中的变形和断裂的聚合物添加CNT，炭黑（CB）和气相生长的碳纤维。断裂构造的形成与演化，即断裂构造的形成与演化。e.银纹，已被研究，以澄清CNT的高强度，高纵横比和纳米尺寸所发挥的重要作用。与炭黑相比，碳纳米管对聚合物的断裂韧性有更大的改善作用。结果表明，CB增加了银纹形成的位点数量，而CNT由于其特定的性质和几何形状而增加了银纹生长所需的能量。与侧面切口的膜相比，表面切口的膜显示出更显著的CNT添加效果。利用断裂力学的基本原理和有限元分析方法对这些结果进行了合理化分析。结果发现，表面切口的膜具有较大的比例的塑性变形区相比，侧切口的膜和CNT的添加，以增加断裂的塑性功的效果是强调与表面切口的膜。总之，本研究阐明了CNT添加由于其特定的性质和几何形状而产生的基本影响，并提出了CNT添加效果最有效的材料几何形状。

In recent years an increasing number of studies have been published reporting mechanical properties of polymers added with carbon nanotubes (CNT). The addition of CNT does not necessarily improve the mechanical properties of polymers. The diversity of experimental results comes from the creation of defects due to aggregation of CNT and utilization of different specimen geometries, in addition to the difference in the CNT/polymer interaction depending on the kinds of polymers and the surface state of CNT. In the present study, time-resolved small-angle X-ray scattering measurements have been conducted using synchrotron radiation during deformation and fracture of processes of polymers added with CNT, carbon black (CB) and vapor grown carbon fiber. The formation and evolution of the precursory structure of fracture, i. e. crazes, have been investigated to clarify the essential effects of CNT exerted by their high strength, high aspect ratio and nanosize. As compared with CB, CNT showed larger effects to improve the fracture toughness of polymers. It was obtained that CB increases the number of sites where the crazes form whereas CNT increases the energy needed for craze growth due to their particular properties and geometries. The surface-notched films showed more significant effects of CNT addition as compared with the side-notched films. The essential work of fracture method and the finite element analysis were employed to rationalize these results. It was found that the surface-notched films have larger fraction of plastic deformation zone as compared with the side-notched films and the effect of the CNT addition to increase the plastic work of fracture is emphasized with the surface-notched films. In summary, the present study elucidated the essential effects of CNT addition exerted due to their particular properties and geometries, and suggested the material geometries with which the effects of CNT addition arise most effectively.