Heterogeneous Wettability-Based Construction of Two-Phase Interfaces for Underwater Reversible Adhesion.

Underwater smart adhesives with switchable adhesion have attracted significant attention for applications in marine engineering and biomedical fields. However, achieving both robust adhesion and rapid on-demand detachment in aquatic environments remains a critical challenge. Inspired by the diving bell spider, we propose a design strategy based on heterogeneous wettability surfaces to achieve switchable adhesion between two surfaces. The heterogeneous wettability surface design confines the oil phase within air cavities formed in superhydrophobic (lipophilic) regions, thereby creating annular oil rings, which establish stable oil/water interfaces that spatially isolate the internal water bridge from the external aquatic environment. The Laplace pressure difference generated at the oil/water interfaces induces robust adhesion between surfaces. In addition, the adhesion strength can be linearly enhanced by constructing multiple, uniformly arranged oil/water interfaces. Rapid on-demand separation can also be achieved through controlled electrolysis of the internal water bridge by applying voltage between the surfaces. Finally, we demonstrate the practical applicability of this adhesive by integrating it into an unmanned underwater vehicle (UUV) for efficient underwater anchoring and ship-hull hitchhiking, highlighting its broad application potential in underwater engineering scenarios.