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Carbon Nanotube Length Governs the Viscoelasticity and Permeability of Buckypaper

机译：碳纳米管的长度控制着Buckypaper的粘弹性和渗透性

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The effects of carbon nanotube (CNT) length on the viscoelasticity and permeability of buckypaper, composed of (5,5) single-walled CNTs (SWCNTs), are systematically explored through large-scale coarse-grained molecular dynamics simulations. The SWCNT length is found to have a pronounced impact on the structure of buckypapers. When the SWCNTs are short, they are found to form short bundles and to be tightly packed, exhibit high density and small pores, while long SWCNTs are entangled together at a low density accompanied by large pores. These structure variations contribute to distinct performances in the viscoelasticity of buckypapers. The energy dissipation for buckypapers with long SWCNTs under cyclic shear loading is dominated by the attachment and detachment between SWCNTs through a zipping-unzipping mechanism. Thus, the viscoelastic characteristics of buckypapers, such as storage and loss moduli, demonstrate frequency- and temperature-independent behaviors. In contrast, the sliding-friction mechanism controls the energy dissipation between short SWCNTs when the buckypaper is under loading and unloading processes. Friction between short SWCNTs monotonically increases with rising length of SWCNTs and temperature. Therefore, the tan δ , defined as the ratio of the loss modulus over the storage modulus, of buckypaper with short SWCNTs also increases with the increment of temperature or SWCNT length, before the SWCNTs are entangled together. The permeability of buckypapers is further investigated by studying the diffusion of structureless particles within buckypapers, denoted by the obstruction factor ( β ). It is found to be linearly dependent on the volume fraction of SWCNTs, signifying a mass-dominated permeability, regardless of the structure variations induced by different SWCNT lengths. The present study provides a comprehensive picture of the structure-property relationship for buckypapers composed of SWCNTs. The methodology could be used for designing multifunctional buckypaper-based devices.
机译：通过大规模的粗颗粒分子动力学模拟，系统地探索了碳纳米管长度对由（5,5）单壁CNT（SWCNT）组成的巴克纸的粘弹性和渗透性的影响。发现SWCNT的长度对布基纸的结构有明显的影响。当SWCNT短时，发现它们形成短束并且紧密堆积，表现出高密度和小孔，而长SWCNT以低密度缠结在一起并伴随着大孔。这些结构变化有助于巴克纸的粘弹性具有独特的性能。具有长SWCNT的布基纸在循环剪切载荷下的能量耗散主要取决于SWCNT之间通过拉链和拉开机制的连接和分离。因此，巴基纸的粘弹性特征，例如存储和损耗模量，表现出与频率和温度无关的行为。相反，当布基纸处于装卸过程中时，滑动摩擦机制控制着短SWCNT之间的能量耗散。短SWCNT之间的摩擦随着SWCNT长度的增加和温度的升高而单调增加。因此，在SWCNT缠结在一起之前，具有短SWCNT的布基纸的tanδ（损耗模量与储能模量之比）也随温度或SWCNT长度的增加而增加。通过研究无结构颗粒在巴克纸内的扩散，以阻滞因子（β）表示，进一步研究了巴克纸的渗透性。发现它与SWCNT的体积分数线性相关，表示质量主导的磁导率，而与不同SWCNT长度引起的结构变化无关。本研究提供了由SWCNT组成的巴克纸的结构-性质关系的全面描述。该方法可用于设计基于buckypaper的多功能设备。

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