Solution Processing of Long Carbon Nanotubes: from Fundamentals to Applications

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Wang, Peng
Wang, YuHuang
Single-walled carbon nanotubes (SWCNTs) are one of the most intensively studied nanomaterials due to their extraordinary mechanical, electrical, and optical properties. Attaining aqueous solutions of individual SWCNTs is the critical first step for harnessing their outstanding properties and applying them in many applications and further processing, such as sorting, imaging, and sensing. However, the current ultrasonication-then-ultracentrifugation approach inevitably introduces defects to SWCNTs and cuts the nanotubes into smaller pieces, compromising the electrical and mechanical properties of this otherwise remarkable material. In this dissertation, we introduce an unexpectedly simple approach that completely eliminates the need for ultrasonication, and nondestructively disperses SWCNTs in aqueous solution, so that the synthetic lengths of SWCNTs can be preserved. The dispersion is achieved by using surfactants to wrap and stabilize the protonated SWCNTs by simple acid-base neutralization reactions. The result is that the protons on SWCNTs are replaced by surfactants, and thus, we name this method “superacid-surfactant exchange (S2E).” In chapters 2-4, we demonstrate the length of dissolved SWCNTs by S2E can be 4-10 times longer than the sonicated controls, thereby significantly improving the optical, electrical and electromechanical properties. We further find that by tuning the concentrations of SWCNTs in this S2E process, short nanotubes can be selectively extracted out, allowing separation of the long carbon nanotubes (>10 µm). In chapter 5, we show that long SWCNTs can behave like mechanical reinforcing structures that enhance the mechanical strength of graphene through π-π interactions without sacrificing much of the outstanding transparency of graphene. This fact has enabled the fabrication of the mechanically strong yet ultrathin graphene/SWCNTs hybrid structure (G+T) for operando probing of the electrical double layer at the electrode-electrolyte interface by X-ray photoelectron. Finally, as a ramification result from the S2E process, chapter 6 describes the scalable synthesis of organic-color-center tailored SWCNTs.