The interface, as the weakest point of a polymer composite, determines the comprehensive performance, especially in a polarity/nonpolarity system featuring poor interfacial adhesion. Here, we report an interfacial manipulation strategy to trigger the preferential adsorption of amide-based self-assembling compounds (NAs) from polypropylene (PP) melts onto the surface of natural fiber (NF) as a result of hydrogen bonding and then promote the epitaxial growth, into root-like NF fiber with interfacial interlocking effects. The unique interface constructed by the grown NA fibers rendered the PP/NF composite with strong interfacial adhesion. The substantial increases of 64.4%, 77.9%, and 94.4% in interfacial shear strength, interfacial friction, and debonding energy are achieved, respectively, in comparison to conventional NF/PP composite. Finally, the working principle of the laterally grown NA fibers on the interfacial enhancement was established based on the fracture morphology after the microbond test. This study can effectively solve the interfacial problems of a polymer composite featuring limited interfacial adhesion, via simple one-step physical blending, without any preliminary surface treatment or "soft" compatibilizers.

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Stretchable conductors are essential assembly units of next-generation flexible electronics, requiring excellent conductivity and stretchability simultaneously. However, poor interfacial adhesion between conductive fillers and polymer matrixes often triggers the relative slippage and dislocation of the conductive network, deteriorating the final conductivity. Herein, we constructed interlocking interfaces in a polyurethane (PU) conductive composite by introducing brush-like carbon fibers (CFs) with laterally grown zinc oxide nanowires (ZnO NWs). The ZnO NW-enabled construction of the functional interfaces integrated the CFs tightly with the polymer matrix to greatly improve the interfacial adhesion and suppress the sliding displacement of conductive fillers upon external load, contributing to excellent mechanical strength and conductive stability. Specifically, the combination of high mechanical strength (7.19 MPa) and stable conductivity (26.3 S/m under 100% strain, approaching 30 S/m of the initial conductivity) was demonstrated for the brushlike CF/PU film. Finally, the application potential of the novel stretchable conductor as a thermal therapy unit and connecting wire in a flexible circuit was explored successfully under complex dynamic deformations. Accordingly, this inspiring result creatively combines the interface geometry with conductive stability, and offers a facile and effective route to prepare excellent stretchable conductors, which can be easily applied to other conductive composites.

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