Alian A R, Meguid S A
Mechanics and Aerospace Design Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, ON M5S 3G8, Canada.
Phys Chem Chem Phys. 2017 Feb 8;19(6):4426-4434. doi: 10.1039/c6cp07464b.
Most existing molecular dynamics simulations in nanoreinforced composites assume carbon nanotubes (CNTs) to be straight and uniformly dispersed within thermoplastics. In reality, however, CNTs are typically curved, agglomerated and aggregated as a result of van der Waal interactions and electrostatic forces. In this paper, we account for both curvature and agglomeration of CNTs in extensive molecular dynamic (MD) simulations. The purpose of these simulations is to evaluate the influence of waviness and agglomeration of these curved and agglomerated CNTs on the interfacial strength of thermoset nanocomposite and upon their load transfer capability. Two aspects of the work were accordingly examined. In the first, realistic carbon nanotubes (CNTs) of the same length but varied curvatures were embedded in thermoset polymer composites and simulations of pull-out tests were conducted to evaluate the corresponding interfacial shear strength (ISS). In the second, the effect of the agglomerate size upon the ISS was determined using bundles of CNTs of different diameters. The results of our MD simulations revealed the following. The pull-out force of the curved CNTs is significantly higher than its straight counterpart and increases further with the increase in the waviness of the CNTs. This is attributed to the added pull-out energy dissipated in straightening the CNTs during the pull-out process. It also reveals that agglomeration of CNTs leads to a reduction in the ISS and poor load transferability, and that this reduction is governed by the size of the agglomerate. The simulation results were also used to develop a generalized relation for the ISS that takes into consideration the effect of waviness and agglomeration of CNTs of CNT-polymer composites.
大多数现有的纳米增强复合材料分子动力学模拟都假定碳纳米管（CNT）是直的，且在热塑性塑料中均匀分散。然而，实际上由于范德华相互作用和静电力，碳纳米管通常是弯曲、团聚和聚集的。在本文中，我们在广泛的分子动力学（MD）模拟中考虑了碳纳米管的曲率和团聚。这些模拟的目的是评估这些弯曲和团聚的碳纳米管的波纹度和团聚对热固性纳米复合材料界面强度及其载荷传递能力的影响。因此，对工作的两个方面进行了研究。第一，将长度相同但曲率不同的实际碳纳米管嵌入热固性聚合物复合材料中，并进行拔出试验模拟以评估相应的界面剪切强度（ISS）。第二，使用不同直径的碳纳米管束确定团聚尺寸对界面剪切强度的影响。我们的分子动力学模拟结果表明如下。弯曲碳纳米管的拔出力明显高于直碳纳米管，并且随着碳纳米管波纹度的增加进一步增大。这归因于在拔出过程中使碳纳米管变直所消耗的额外拔出能量。研究还表明，碳纳米管的团聚导致界面剪切强度降低和载荷传递能力差，并且这种降低受团聚尺寸的控制。模拟结果还用于建立一个考虑碳纳米管 - 聚合物复合材料中碳纳米管波纹度和团聚影响的界面剪切强度通用关系式。
