Chemically Surface Functionalized Carbon Black for Flexible Electrothermal Heating

ABSTRACT Carbon black (CB) is attractive for electrothermal films owing to its low cost and facile processability, but agglomeration and weak filler‐matrix interactions often undermine conductivity, adhesion, and heating uniformity. Here, we regulate the CB‐polyurethane (PU) interface using 3‐Glycidyloxypropyltrimethoxysilane (GPTMS) and elucidate how the silane dosage governs CB dispersion, percolation behavior, and the Joule‐heating performance of CB/PU films. GPTMS grafts onto CB via hydrolysis to form Si‐O‐C/Si‐O‐Si interfacial linkages, while the epoxy group undergoes ring‐opening reactions with PU, thereby enhancing CB‐PU coupling. Moderate GPTMS loadings (GPTMS:CB = 1:1–3:1) yield well‐dispersed, continuous conductive networks in PU, producing low resistivity, strong adhesion, and substantially improved thermal uniformity. In contrast, excessive GPTMS (≥ 4:1) promotes siloxane self‐condensation, reinstates CB aggregation, and introduces insulating interlayers that disrupt electron pathways. Interestingly, the CB volume fraction‐dependent conductivity shows that silane modification increases the percolation threshold by thickening interfacial layers (tunneling barrier) yet steepens the post‐threshold conductivity rise due to more effective cluster growth. Printed films (with PU:CB = 5:1, GPTMS:CB = 3:1) demonstrate application‐level performance that under 5 V, they rapidly reach ~55°C within 15 s with uniform temperature fields and retain both heating and adhesion after repeated bending. This study establishes a mechanistic framework linking silane‐mediated interfacial chemistry to network topology and device metrics and provides a practical processing window (GPTMS:CB ≈ 2–3:1) for scalable, durable CB‐based electrothermal films and wearable heaters.