Drying-controlled internal structure for enhanced post-treatment efficiency in high-strength carbon nanotube fibers

초록

Mechanical failure in carbon nanotube fibers (CNTFs) is primarily governed by inter-bundle slippage due to weak van der Waals interactions; thus, placing covalent crosslinks at bundle-bundle interfaces is critical for reinforcement. However, conventional functionalization approaches offer limited spatial control over crosslinking within the hierarchical fiber structure. Here, we demonstrate a wet-state engineering strategy that exploits the drying process during CNTF fabrication to regulate crosslinking-reagent infiltration and thereby target specific crosslinking sites. Electrochemically active surface area (ECSA) measurements confirmed that reagent-accessible CNT surface area decreases with increasing drying degree, demonstrating that internal reagent accessibility is governed by drying state. In wet CNTFs, extensive reagent penetration yields broadly distributed functionalization rather than targeted interfacial reinforcement. In fully dried fibers, severe densification and hydrophobic recovery restrict reagent access to the outer region. Partially dried fibers, however, allow reagents to reach interbundle regions, promoting covalent bridging precisely where load transfer is most limited. Consequently, crosslinked partially dried CNTFs (c-pd-CNTF) showed the highest reinforcement, with specific tensile strength and stiffness reaching 146% and 160% of pristine CNTFs (p-CNTF), respectively. In situ Raman analysis revealed the highest G ' peak shift rate of 25.2 cm- 1/% for c-pd-CNTF, confirming superior load transfer efficiency. Furthermore, c-pd-CNTF retained mechanical performance under water and isopropyl alcohol (IPA) exposure and exhibited superior knot strength and dynamic work recovery. These findings establish drying-state control as a critical structural design parameter governing CNTF microstructure, reagent accessibility, and post-treatment efficiency.

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