Kayang Kevin W, Banna Abu Horaira, Volkov Alexey N
Department of Mechanical Engineering, University of Alabama, Seventh Avenue, Tuscaloosa, Alabama 35487, United States.
Langmuir. 2022 Feb 15;38(6):1977-1994. doi: 10.1021/acs.langmuir.1c02632. Epub 2022 Feb 1.
The effect of nanotube chirality on the mechanical properties of materials composed of single-walled carbon nanotubes (CNTs) is poorly understood since the interfacial load transfer in such materials is strongly dependent on the intertube interaction and structure of the nanotube network. Here, a combined atomistic-mesoscopic study is performed to reveal the effect of CNT diameter on the deformation mechanisms and mechanical properties of CNT bundles and low-density CNT films with covalent cross-links (CLs). First, the pullout of the central nanotube from bundles composed of seven (5,5), (10,10), (20,20), (17,0), and (26,0) CNTs is studied in molecular dynamics simulations based on the ReaxFF force field. The simulations show that the shear modulus and strength increase with decreasing CNT diameter. The results of atomistic simulations are used to parametrize a mesoscopic model of CLs and to perform mesoscopic simulations of in-plane tension and compression of thin films composed of thousands of cross-linked CNTs. The mechanical properties of CNT films are found to be strongly dependent on CNT diameter. The film modulus increases as the CNT diameter increases, while the tensile strength decreases. The in-plane compression is characterized by collective bending of whole films and order-of-magnitude smaller compressive strengths. The films composed of (5,5) CNTs exhibit the ability for large-strain compression without irreversible changes in the material structure. The stretching rigidity of individual nanotubes and volumetric CL density are identified as the key factors that dominate the effect of CNT chirality on the mechanical properties of CNT films. The film modulus is affected by both CL density and stretching rigidity of CNTs, while the tensile strength is dominated by CL density. The obtained results suggest that the on-demand optimization of the mechanical properties of CNT films can be performed by tuning the nanotube chirality distribution.
由于此类材料中的界面载荷转移强烈依赖于纳米管间的相互作用和纳米管网络结构，所以纳米管手性对由单壁碳纳米管（CNT）组成的材料机械性能的影响尚不清楚。在此，进行了一项原子尺度与介观尺度相结合的研究，以揭示CNT直径对具有共价交联（CL）的CNT束和低密度CNT薄膜的变形机制及机械性能的影响。首先，基于ReaxFF力场在分子动力学模拟中研究了由七根（5,5）、（10,10）、（20,20）、（17,0）和（26,0）CNT组成的束中中心纳米管的拔出情况。模拟结果表明，剪切模量和强度随CNT直径减小而增加。原子模拟结果用于对CL的介观模型进行参数化，并对由数千根交联CNT组成的薄膜进行面内拉伸和压缩的介观模拟。发现CNT薄膜的机械性能强烈依赖于CNT直径。薄膜模量随CNT直径增加而增大，而拉伸强度则降低。面内压缩的特征是整个薄膜的集体弯曲且压缩强度小几个数量级。由（5,5）CNT组成的薄膜表现出大应变压缩能力且材料结构无不可逆变化。单个纳米管的拉伸刚度和体积CL密度被确定为主导CNT手性对CNT薄膜机械性能影响的关键因素。薄膜模量受CL密度和CNT拉伸刚度的共同影响，而拉伸强度则主要由CL密度决定。所得结果表明，通过调整纳米管手性分布可实现对CNT薄膜机械性能的按需优化。
