Single-Walled Carbon Nanotube Aerogels: Synthesis, Characterization, Application

This thesis contributes to the field of developing a new class of multifunctional porous materials for various applications by creating networks of single-walled carbon nanotubes (SWCNTs) in quasi-2D and 3D. Synthesis and characterizations of various SWCNT-based aerogels, and their applications as heat sinks and transparent electrodes in organic photovoltaics (OPVs) are described.;Flexibility was also added to the fragile SWCNT aerogels by coating graphene nanoplates on a surface of SWCNT struts and nodes between SWCNTs. Graphene-coated (Gr-coated) SWCNT aeorgels showed superelasticity with a complete recovery from large strain > 80% and fatigue resistance while maintaining high porosity ≥ 99%. Strikingly, the graphene-coated SWCNT aerogel had temperature-invariant mechanical properties in the temperature range from -100 °C to 500 °C within the linear viscoelastic regime and the temperature range from -100 °C to 300 °C at larger strains (> 80%). The origins of the temperature-invariant mechanical properties within the linear viscoelastic regime and in the larger strain range were due to the inherent strength of carbon nanotube springs based on stable carbon-carbon bonds in graphitic walls of carbon nanotubes above 1500 °C along with van der Waals interactions between SWCNTs and graphene coating, respectively. In addition, we have fabricated a series of near-ideal open-cell Gr-coated SWCNT aerogels with varying density by controlling bundling of SWCNT struts in the aerogels with PAN polymers during compaction and by converting PAN into graphene. Gr-coated SWCNT aerogels scaled well with density with a power-law exponent of ≈ 2 over a wide density range from 16 to 400 mg mL-1. An efficient load transfer between ligaments and load-bearing purely by bending of SWCNT struts composing cell walls ensures a scaling characteristic with n ≈ 2, which demonstrates a highly efficient open-cell structure of a Gr-coated SWCNT network.;SWCNT aerogels were backfilled with polydimethylsiloxane (PDMS) to create transparent and non-transparent composites, which were stretchable and bendable. The highest transparency achieved was ≈ 93% with the SWCNT aerogel with thickness of ≈ 3 µm. The transparent and non-transparent elastic conductors showed excellent electrical stability with minimal degradation in electrical conductivity by ≈ 16% under tensile strain up to 100%. The composite have potential applications in the field of OPVs as stretchable transparent electrodes.;Low density SWCNT aerogels were created by critical point drying aqueous SWCNT hydrogels, and they were 3 dimensional (3D) macroscopic network structure. High density SWCNT aerogel thin films (quasi-2D) were fabricated by concentrating the hydrogel thin films via directed evaporation of solvent from the hydrogels. SWCNT aerogels could be made into virtually any shapes and sizes. The highest electrical conductivity was achieved with the high density SWCNT aerogel thin films, and the conductivity value reached 167 S cm-1. The aerogels had an open porous network structure, which was confirmed by the power-law dependence of the aerogel with the exponent of ≈ 2. The thermal management characteristic of the SWCNT aerogels was determined, and it was found that the aerogels enhanced heat transfer in a forced convective process by ≈ 85% compared to the case without the aerogels presumably due to their large porosity and large surface area-to-volume ratio. In addition, the aerogel thin films with thickness of ≤ 25 µm were transparent enough to be used for optoelectrical devices. An application of the high density SWCNT aerogel thin films as transparent anodes for OPVs was successful with power conversion efficiency of 1%, which could be further improved by process optimization.