Underwater Structurally‐Colored Adhesives for Visualized Adhesion Monitoring in Aqueous Media

Abstract Assessment of the local strain/stress changes of adhesives is highly desirable for their service to avoid premature failure. However, monitoring local strain/stress variations in adhesives in practical settings remains challenging, especially in aqueous media. Here, an underwater structurally‐colored adhesive for visualized local strain/stress monitoring in aqueous media is reported. The structurally‐colored adhesive is obtained by shearing composites of poly(butyl acrylate‐ co ‐acrylic acid) copolymer and carboxylated polystyrene colloidal particles. The resultant structurally‐colored adhesive exhibits underwater adhesive strength (i.e., 238 kPa for stainless steel substrates) to various substrates (e.g., metals and plastics) thanks to hydrophobic segments and carboxyl groups. Notably, they can shift color in response to external force, enabling real‐time visual monitoring of localized strain/stress changes. As a proof of concept, the structurally‐colored adhesive can be used to seal a leaking hole on a bottle or tube, and it can precisely visualize the localized pressure distribution, providing critical information on the adhesion performance and the local pressure. These distinctive properties make the structurally‐colored adhesive suitable for application in wet environments as a real‐time visual pressure tracking device.