Liquid-free covalent reinforcement of carbon nanotube dry-spun yarns and free-standing sheets

High-Resolution X-ray Spectromicroscopy Reveals Process-Structure Correlations in sub-5-μm Diameter Carbon Nanotube-Polymer Composite Dry-Spun Yarns

“…This provides critical information for understanding the quantity of void space within the yarn available for infiltrating with a reinforcing matrix material. A majority of the porosity values lie between 0.86 and 0.38 (Figure b), which approaches the theoretical lower limit of 0.26 for close-packed hollow cylinders (for a 10 nm diameter, which is a similar value for the CNTs used in this study according to TEM observations). Again, the inset shows the 600 μm track width data set scales fairly along the −2 exponential model curve over the expanded diameter range.…”

“…These peripheral bundles appear thicker as they get coated during the vapor-phase polymer deposition, while SEM shows that the surface texture of the main body of the yarn becomes smoother as the polymer fills gaps between CNTs. STXM shows that the internal structure may still have heterogeneities and small voids that are not entirely coated (as previously reported by SEM cross-section analysis), but these are greatly reduced upon thermal cross-linking. In this final cross-linked state, both the SEM and STXM images reveal a smooth, homogeneous structure, which explains the recently reported enhanced mechanical properties of our cross-linked CNT yarns .…”

“…To mechanically reinforce the dry-spun CNT yarns (which are held together by van der Waals forces and mechanical entanglement), we introduced a vapor-phase polymerization of poly glycidyl methacrylate (PGMA) to fill the voids between CNTs and then thermally cross-linked the polymer to hinder CNT movement and load-induced bundle reorganization (Figure S4). The yarns exhibit clear increases in mass density at each step of the polymer reinforcement treatment.…”

“…Details of the polymer synthesis chamber and conditions were reported in our previous work . CNT yarns were coated with poly glycidyl methacrylate (PGMA) by iCVD (GVD Co. iLab coating system) at 200 mTorr using glycidyl methacrylate (GMA, Sigma-Aldrich, 97%) as monomer, tert- butyl peroxide (TBPO, Sigma-Aldrich, 98%) as initiator, a hot filament held at approximately 155 °C, and the CNT sample close to room temperature.…”

“…As the yarn twist density was increased (from 15,000 to 150,000 turns per meter) for a given forest track width, the yarn diameter decreased (4.4–1.4 μm) and density increased (0.55–1.26 g·cm –3 ) ubiquitously scaling with diameter d according to ρ ∼ d –2 . In composite yarns, the spectro-microscopy capabilities of STXM enabled analysis of the spatial distribution (averaged along either the yarn length or width) of the oxygen-containing polymer (∼30% weight fraction), demonstrating nearly perfect filling of the voids between CNTs with our vapor-phase polymer coating and cross-linking process . These quantitative correlations highlight the intimate connections between processing conditions and yarn structure, representing data sets for CNT yarns, especially in this ultrafine diameter regime of single-digit micrometers which are of interest for several high-end engineering applications, including target fabrication at the National Ignition Facility (NIF).…”