Abstract
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 , 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 (). 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.
Highlights
Carbon nanotubes (CNTs) with persistence lengths L p of the order of several microns are one of the most attractive nanomaterials due to their exceptional mechanical, thermal and electrical properties [1,2,3,4,5]
The fully-relaxed microstructure of single-walled CNTs (SWCNTs) buckypaper is determined by the competition between the long-range van der Waals (vdW) attraction and bending energy penalty due to the high stiffness of individual CNTs
If we inspect the individual configurations of SWCNTs
Summary
Carbon nanotubes (CNTs) with persistence lengths L p of the order of several microns are one of the most attractive nanomaterials due to their exceptional mechanical, thermal and electrical properties [1,2,3,4,5]. Afterwards, the suspension can be further membrane filtered under positive and negative pressure, yielding a stable film During this process, the CNTs exhibit the strong tendency to aggregate due to their long range van der Waals (vdW) interactions, forming either bundle-dominated or entanglement-dominated CNT networks [11,12]. The Young’s modulus and breaking strength of single-walled CNTs (SWCNTs) buckypapers are up to 4.2 GPa and 33 MPa, respectively [14,15,16,17]. Their mechanical properties could be further tuned by adjusting the density and the CNT diameter [18,19]. All of these properties make buckypapers attractive nanomaterials with many potential applications, such as sensors, actuators, filtration and distillation devices
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