Interface Wetting Driven by Laplace Pressure on Multiscale Topographies and Its Application to Performance Enhancement of Metal-Composite Hybrid Structure.

Surface topography reconstruction is extensively used to address the issue of weak bonding at the polymer-metal interface of metal-composite hybrid structure, while enhancement from this approach is seriously impaired by insufficient interface wetting. In this study, the wetting behavior of polymer on aluminum surfaces with multiscale topographies was theoretically and experimentally investigated to realize stable and complete wetting. Geometric dimensions of multiscale surface topographies have a notable impact on interfacial forces at the three-phase contact line of polymer/air/aluminum, and a competition exists between Laplace pressure and bubble pressure in dominating the wetting behavior. Laplace pressure facilitates the degassing of trapped air bubbles in grooves, bringing more robust interfacial wettability to grooves than dimples and grids. Conversely, dimples with excessive dimensions generate interfacial pores, and this intrinsic mechanism is theoretically unraveled. Moreover, different degrees of interface wetting cause variations in bonding strength of polymer-aluminum interface, which changes from ∼18% improvement to ∼17% reduction compared to original strength. Finally, groove topography perfectly achieved complete wetting between polymer and aluminum and consequently improved flexure performance by over 11% for the aluminum-carbon fiber hybrid side impact bar, which verifies the importance of complete wetting at a part scale. This study deepens the understanding of wetting behavior and clarifies the intrinsic correlation between interfacial bonding performance and surface topography.