In Situ Decoding of Vitrimer Topological Evolution: A Non-Invasive, External Stress-Free Approach via Hierarchical...

Vitrimers are covalent adaptable networks (CANs) that undergo thermally activated topological rearrangement via dynamic bond exchange, enabling reprocessability and intrinsic self-healing. However, precise, real-time identification of the topological transition temperature (T_v) remains challenging, as conventional methods are inherently stress- and protocol-dependent. Here, we present a hierarchically structured piezoresistive sensing strategy based on dual-scale CNT-integrated conductive networks. A mesoscale CNT-decorated glass fibrous web (G-CNT) and a nanoscale CNT/EPON percolation network are synergistically integrated to enable in situ, external-stress-free electrical tracking of disulfide-containing epoxy vitrimer network formation and topological transitions. These multiscale conductive architectures exhibit distinct resistance signatures throughout vitrimer evolution, with pronounced inflection features at T_v arising from bond-exchange-driven rearrangements of conductive pathways. Comparative analysis reveals that interfacial G-CNT meso-networks fabricated via ultrasonic atomization exhibit substantially higher sensitivity, manifested by pronounced resistance decreases at T_v (ΔR_v = -10.9% to -20.0%), enabling instant detection of local topological rearrangements. In contrast, bulk CNT/EPON networks display attenuated resistance responses (ΔR_v = -4.3% to -9.4%) associated with matrix-level percolation restructuring. These electrical signatures are corroborated by differential scanning calorimetry, dynamic mechanical analysis, rheology, and dielectric analysis, establishing a direct structure-dynamics-signal correlation. This stress-free, multiscale sensing paradigm provides a scalable route for intrinsic T_v identification and process-aware diagnostics in recyclable and adaptive vitrimer-based composites.