UC San Diego

Single-walled carbon nanotubes (SWCNTs) are promising bottom-up building materials due to their superior properties. However, the lack of an effective method to arrange large quantities of SWCNTs poses an obstacle toward their applications. Existing studies to functionalize, disperse, position, and assemble SWCNTs provide a broad understandings regarding SWCNTs behavior, especially in aqueous electrolyte solution. Inspired by ionic polymer metal composite (IPMC) materials, this dissertation envisions fabrication of orderly SWCNTs network structure via their ionic clustering-mediated self -assembly. SWCNTs tend to bundle together due to inter- nanotube VDW attractions, which increase with nanotube length. The author seeks short SWCNTs with long chain molecules bearing ionic termini to facilitate debundling and self-assembly in aqueous electrolyte solution through end-clustering. First, a simple model was applied based on essential physical factors. The results indicated that SWCNTs must be shorter than 1̃00 nm to achieve stable network structures. Experiments were then carried out based upon the results. Short SWCNTs (50-100 nm) were end- functionalized with hexaethylene glycol (HEG) linkers bearing terminal carboxylate anions. Both 2D and 3D network structures were observed after placing the functionalized SWCNTs in aqueous electrolyte (sodium ion). The network structures were characterized by microscopic and spectroscopic methods. A novel approach was applied via electron tomography to study the 3D structures of SWCNTs structure in aqueous electrolyte. Free energy analysis of the SWCNTs network structure was implemented with the assistance of both analytical tools and molecular simulations. The results indicate that, when a cluster is formed by three functionalized SWCNTs ends, the resulting network structure is most stable. Indeed, 72% of the clusters/joints were formed by three nanotubes, as observed in experiments. Finally, Monte Carlo simulations of coarse-grained SWCNTs were implemented to understand the behavior of SWCNTs. SWCNTs clusters were observed as a result of this simulation