Magnetically actuated functional gradient nanocomposites for strong and durable bioinspired interfaces/surfaces

Biological systems have evolved various functional gradients within interfacial and surface regions to fulfil unusual mechanically-challenging demands [1-3]. Exploring these design principles of nature materials into practice remains difficult, however, due to the lack of proper processing technique for analogous gradients within narrow regions. Here we report a facile and cost-effective technique enabling the construction of a variety of bioinspired gradient interfaces/surfaces that are not accessible using state-of-the-art technologies. This technique utilizes magnetic actuation to control spatial distribution of nano-sized reinforcements inside polymer matrices, being able to generate functional gradient nanocomposites (FGNCs) with controllable stiff-to-soft or soft-to-stiff transition within regions as narrow as 10 microns (Fig. 1). We demonstrate the robustness and universality of this technique by implementing the FGNCs into three mechanically-challenging applications: 1) functional gradient interlayer for strong, intact, and ultra-durable jointing between dissimilar materials; 2) functional gradient coating for hard, wear-resistant, and long-lasting surface protections; and 3) functional gradient pillars for flexible, structurally stable, and reusable biomimetic adhesives. The presented study opens a new route for designing and developing materials/structures with optimized performances by simply modifying the spatial distributions of material composition. This route can potentially be integrated into advanced manufacturing techniques [4, 5] and applied to numerous surface/interface fields to achieve unparalleled combinations among various critical properties.