Deploy and Destroy: Self-Immolative Sidechains for Revealing Highly Conductive Carbon Nanotube Electronics

Abstract

Single-walled carbon nanotubes (SWNTs) are promising materials for high-performance electronic devices, but their practical applications are limited by poor purity and solubility. Commercially available SWNTs typically consist of a mixture of semiconducting (sc-) and metallic (m-) nanotubes and are insoluble in most common solvents. Conjugated polymers can selectively disperse either sc- or m-SWNTs and enhance their solubility; however, the electrical conductivity of polymer-wrapped SWNTs is often hindered by the insulating nature of the polymer sidechains. This thesis presents a novel poly(fluorene-co-phenylene) conjugated polymer incorporating self-immolative linkers within its sidechains. These linkers are protected by tert-butyldimethylsilyl (TBS) ether groups and undergo a 1,6-elimination reaction upon treatment with tetra-n-butylammonium fluoride (TBAF), effectively cleaving the sidechains. Sonication of this polymer with SWNTs in tetrahydrofuran (THF) yields concentrated dispersions, which are used to fabricate thin films. Upon TBAF treatment, the sidechains are eliminated as carbon dioxide and diol byproducts, which can be easily removed by solvent washing. The electrical conductance of the resulting SWNT films increased by approximately 60-fold after sidechain removal, demonstrating a simple and effective strategy for generating highly conductive SWNT materials. This method enables the straightforward fabrication of transparent conductive films with significantly reduced sheet resistance while maintaining high optical transmittance, particularly when applied to flexible Mylar substrates. Furthermore, integration with polydimethylsiloxane (PDMS) enabled the creation of skin-like, ultra-wrinkled conductive surfaces using a simple, cost-effective, and reproducible approach. The resulting pressure sensors exhibited excellent performance, with a sensitivity of 1,655 kPa⁻¹ across a wide pressure range (0.003–70.1 kPa, R² = 0.9931), rapid response times, and long-term stability. Beyond substrate-based films, composite materials were also developed by blending the polymer-SWNT complex with cellulose-based matrices. Mixing the complex with microcrystalline cellulose (MCC) in the presence of TBAF yielded flexible, conductive buckypapers with an optimal balance of mechanical strength (tensile modulus: 161 ± 10 MPa; yield strain: 11 ± 2%) and conductivity (107 ± 4 S/m). Additionally, aerogels were fabricated by combining cellulose nanocrystals (CNCs) with the polymer-SWNT complex via solvent exchange and freeze-drying. These aerogels demonstrated enhanced elasticity, conductivity, and mechanical integrity, making them strong candidates for piezoresistive pressure sensing applications.