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

Abstract

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 (b-CNTs, 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 re-establishes 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.