Engineering Ionic Liquid-Modified Silicon Carbide Elastomer Composites for Enhanced Thermochromic Responsiveness in Smart Flexible Sensors

Flexible thermochromic sensors emerge as next-generation smart materials for adaptive temperature sensing, thermal management, and multifunctional device applications. In this study, nitrile butadiene rubber (NBR) composites incorporating a thermochromic pigment, silicon carbide (SiC), and two distinct ionic liquids (ILs) were systematically investigated. Rheometric analysis at 160 °C revealed that SiC promotes network formation by reducing scorch and vulcanization times (t0.5, t90) and increasing torque increment (ΔM), which correlates with enhanced cross-link density. The introduction of ILs provided a tunable effect on both cure kinetics and network architecture: bmimBF4 acted as a catalytic accelerator, shortening curing times and increasing ΔM, while PMIMTFSI exhibited a plasticizing effect, resulting in lower cross-link density. Stress–strain analysis confirmed these trends, with SiC- and bmimBF4-containing composites displaying higher tensile strength and modulus, whereas C3mimTFSI reduced stiffness but increased extensibility. Thermo-oxidative aging studies over 1, 2, and 3 weeks demonstrated superior aging factors (AF) for SiC- and bmimBF4-based systems, underscoring their resilience against oxidative degradation. Importantly, it was observed that the choice of ionic liquid allows direct control over the thermochromic response: bmimBF4 enabled effective and reversible color transitions at elevated temperatures, while C3mimTFSI suppressed pigment activity within the elastomeric matrix. These results highlight the critical role of ionic liquid chemistry in tailoring both functional and structural properties of thermochromic elastomer sensors.