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    Dynamic polymer network conductive Nanocomposites: Low percolation threshold and Joule-heating-induced network plasticity

    Year: 2022

    Journal: Chem. Eng. J., Volume 443, SEP 1

    Authors: Sang, Zhen; Zhou, Qing; Rajagopalan, Kartik Kumar; Thomas, Edwin L.; Gardea, Frank; Sukhishvili, Svetlana A.

    Organizations: Hagler Institute for Advanced Study at Texas AM University; U.S. Combat Capabilities Devel-opment Command Army Research Laboratory [W911NF-19-2-0264, W911NF-18-2-0232]

    Keywords: Dynamic covalent polymer networks; Electrical conductivity; 3D printing; Permanent shape reconfiguration; CNT nanocomposites

    Diels-Alder-based polymer (DAP) dynamic networks have demonstrated the unique ability to undergo fast temperature-triggered solid-liquid transitions and exhibit solid-state network plasticity, making them exceptional materials for printing, self-healing, and shape morphing. However, the advantages of DAP materials as a matrix for novel nanocomposites have not yet been demonstrated. Herein, we report highly electrically conductive nanocomposites made of a DAP network loaded with branched multi-walled carbon nanotubes (bCNTs, average aspect ratio of 5000). The nanocomposites have an extremely low percolation threshold of 0.04 wt % and are capable of controlled network plasticity via Joule-heating-induced bond exchange. The unprecedented filler dispersion is achieved due to the capability of DAPs to deconstruct upon heating to low-viscosity components that can effectively wet and infiltrate b-CNTs. The dispersed fillers are additionally stabilized by covalent bonds between the DAP matrix and b-CNTs. Upon cooling, the solid-state click DA reaction rapidly reestablishes a crosslinked network, locking the well-dispersed b-CNTs. The nanocomposites can be easily 3D printed within multi-material, self-adhering hybrid constructs, exhibiting tunable mechanical and electrical properties. Dynamic bond exchange can be triggered selectively at different locations in these hybrid constructs, enabling spatiotemporal control of Joule-heating-induced reconfiguration of the material's permanent shape governed by network plasticity.
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