Designing Gradient Cross-Linking Shape Memory Rubber Composites via Aging Strategy for Temperature Sensors

The design of gradient shape memory polymers (GSMPs) is important for their sensor or actuator applications, yet challenging. Herein, we design and prepare GSMP via a gradient aging methodology on nitrile butadiene rubber composites with sulfur covalent and Zn²⁺-CN coordination bonding networks. The gradient characteristics of the GSMP are adequately evaluated by spatially separating them into equal sections. The aging temperature gradient spatially changes chemical components of covalent networks, which is verified by FTIR and UV–vis spectra. SEM and EDS observations show that temperature driven ion diffusion yields gradient distributions of Zn²⁺ ions, achieving a gradient metal–ligand network owing to its high dependence on metal ions. As a result, GSMPs with gradient covalent and coordination cross-linking networks are formed. Importantly, a distinct distribution of glassy temperatures is achieved on this GSMP, leading to its continuous shape recovery response at different positions during the shape memory cycle. The finger-shaped temperature sensors are invented to stably respond over a wide range (9.6–27.0 °C) of thermal triggers using this GSMP. The possible strategies to improve temperature sensing properties of the GSMP composites are further proposed. In addition, our GSMP possesses a timed directional transfer capability. These findings might be meaningful in providing simple methods of preparing GSMPs and showing their great potential in temperature sensors and timed transfer applications.