Shell thickness and defect engineering for eximious thermal, electromagnetic, hydrophobic, and mechanical capabilities in Cu@ammonium gluconate core–shell nanofibers

•A one-step hydrothermal reduction route is developed for the preparation of high-quality Cu@ammonium core–shell nanofibers.•The Cu@AG CSNFs exhibit strong wideband absorption (RLmin = -44.8 dB, d = 1.8 mm, and ABW = 6.24 GHz; 8 wt% load) and efficient wideband RCS Reduction (up to 26.33 dB·m2).•The Cu@AG CSNFs possess a high thermal conductivity (23.07 W/(m·K)) at a low load of 8 wt%, a fast thermal response, terrific working stability, and tunable saturation temperature under low voltage.•The Cu@AG CSNFs exhibit high strength, excellent elasticity, and effective waterproofing.•Mechanism analysis was conducted by theoretical calculations of DOS, PDOS, and E-field distribution. [Display omitted] Cu nanofibers have appeared as promising nanomaterials for application in thermal dissipation and microwave absorption/shielding. However, their practical application is limited by high conductivity, poor impedance matching, and low chemical stability. To mitigate these drawbacks, multifunctional Cu@ammonium gluconate core–shell nanofibers (Cu@AG CSNFs) are prepared via a simple one-step hydrothermal reduction, in which AG shell thickness and defects are adjusted by a competitive growth between AG shell and Cu core at various temperatures. Benefiting from the electron/phonon co-transmission and continuous 3D crosslinked framework, the Cu@AG CSNFs/TPU films exhibit a large thermal conductivity (23.07 W/(m⋅K); 8 wt%), high strength, excellent elasticity, and effective waterproofing. Meanwhile, the film of Cu@AG CSNFs can function as a Joule heater thanks to its fast thermal response, terrific working stability, and excellent repeatability. Besides, the Cu@AG CSNFs possess prominent microwave absorption capability (ABW = 6.24 GHz; 8 wt% load) and stealth performance, resulting from the synergic effect of heterointerfaces, tunable defects, and 1D structure. These properties exceed those of other Cu-based composites. Our work provides both theoretical and experimental evidence for developing high-performance multifunctional polymer-based films, which are expected to be used in challenging environmental conditions, such as heavy rainfall, high humidity, and extreme cold.