Bio-Inspired Hierarchical Carbon Nanotube Yarn with Ester Bond Cross-Linkages towards High Conductivity for Multifunctional Applications.

The cross-linked hierarchical structure in biological systems provides insight into the development of innovative material structures. Specifically, the sarcoplasmic reticulum muscle is able to transmit electrical impulses in skeletal muscle due to its cross-linked hierarchical tubular cell structure. Inspired by the cross-linked tubular cell structure, we designed and built chemical cross-links between the carbon nanotubes within the carbon nanotube yarn (CNT yarn) structure by an esterification reaction. Consequently, compared with the pristine CNT yarn, its electrical conductivity dramatically enhanced 348%, from 557 S/cm to 1950 S/cm. Furthermore, when applied with three voltages, the electro-thermal temperature of esterified CNT yarn reached 261 °C, much higher than that of pristine CNT yarn (175 °C). In addition, the esterified CNT yarn exhibits a linear and stable piezo-resistive response, with a 158% enhanced gauge factor (the ratio of electrical resistance changing to strain change ~1.9). The superconductivity, flexibility, and stable sensitivity of the esterified flexible CNT yarn demonstrate its great potential in the applications of intelligent devices, smart clothing, or other advanced composites.