Abstract
Macroscopic assemblies of carbon nanotubes (CNTs) usually have a poor alignment and a low packing density due to their hierarchical structure. To realize the inherent properties of CNTs at the macroscopic scale, the CNT assemblies should have a highly aligned and densified structure. Shear-aligning processes are commonly employed for this purpose. This work investigates how shear flows affect the rearrangement of CNT bundles in macroscopic assemblies. We propose that buckling behavior of CNT bundles in a shear flow causes the poor alignment of CNT bundles and a low packing density of CNT assemblies; the flow pattern and the magnitude of shear stress induced by the flow are key factors to regulate this buckling behavior. To obtain CNT assemblies with a high packing density, the CNTs should undergo a laminar flow that has a sufficiently low shear stress. Understanding the effect of shear flow on the structure of CNT bundles may guide improvement of fabrication strategies.
Highlights
Carbon nanotubes (CNTs) can form macroscopic assemblies like CNT bers or lms, which typically have hierarchical structures (Fig. 1a).[1,2,3,4] Individual CNTs form compact CNT bundles, in which adjacent CNTs strongly attract each other by strong van der Waals forces due to their closeness;[1,2,5,6,7] these compact bundles seem to have a highly densi ed structure.[1]
We propose that buckling behavior of CNT bundles causes the poor alignment of CNT bundles and the low packing density of CNT assemblies, and that this behavior is dependent on both the ow pattern and the shear stress
Had a at and dense structure with few big aggregated bundles (Fig. 5c). These results show that TC ow can effectively disentangle huge CNT aggregates; this conclusion is consistent with optical microscope (OM) images
Summary
Carbon nanotubes (CNTs) can form macroscopic assemblies like CNT bers or lms, which typically have hierarchical structures (Fig. 1a).[1,2,3,4] Individual CNTs form compact CNT bundles, in which adjacent CNTs strongly attract each other by strong van der Waals (vdW) forces due to their closeness;[1,2,5,6,7] these compact bundles seem to have a highly densi ed structure.[1]. Without introducing damage or using additional materials.[32] We tried to disentangle and align loosely entangled CNT bundles by using shear ow. In order to effectively control the structure of CNT assemblies, it is necessary to clearly understand the effect of shear ow on the disentangling and aligning of bundles. When laminar ow has sufficiently high shear stress, the obtained CNT bundles were highly entangled, which was counterintuitive. Our results can help to increase understanding of the mechanisms of change in the microstructure of CNT materials and may guide development of methods to fabricate CNT materials that have desired structures
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