A Mechanochromic Polymer Based on a PDMS-Incorporated Polydiacetylene-Polyurethane System for Structural Health Monitoring

Mechanochromic sensors have become an attractive method for Structural Health Monitoring (SHM) due to their self-reporting and naked-eye visualization nature, making them ideal for stress-induced crack sensing and damage detection. A mechanochromic polymer film, Poly(MDI–PDA-PDMS-1), with a chromogenic polydiacetylene (PDA) component, was synthesized through a two-step process: copolymerization followed by UV irradiation to cross-link diacetylene templates to produce blue-purple Poly(MDI–PDA-PDMS-1). The Poly(MDI–PDA-PDMS-1) film displayed mechanochromic behavior with a visible color transition from blue-purple at 0% strain to red-orange at 200% strain. The strain-at-break was recorded at 204% with a corresponding stress value of 11.5 MPa. The Poly(MDI–PDA-PDMS-1) sensor was found to be stable under harsh conditions in highly acidic (pH 1.0) and basic (pH 14.0) solutions for 24 h. Importantly, the film was evaluated for crack monitoring in cement–concrete composites under flexural loading, where deformations in the PDA structure triggered a visible color change. Hence, Poly(MDI–PDA-PDMS-1) presents promising potential for self-reporting structural crack monitoring in the SHM process.