Molecular engineering of waterborne polyurethane via ionic liquid intercalation for pressure-insensitive flexible film and fiber temperature sensors

Ionic liquids regulate the hydrogen-bonding structure of WPU hard segments. • The fabricated film and fiber temperature sensors exhibit −2.25%/°C and −2.21%/°C. • Ion-migration conduction makes the sensor pressure-insensitive. • The sensors are practical for breath monitoring, thermal-tactile, and body temperature. Flexible temperature sensors with high sensitivity and good mechanical stability are of great significance in wearable medical and human-computer interaction fields. However, traditional thermistors are usually limited by the strong cross-sensitivity between temperature and mechanical strain. To solve this problem, this paper proposes a molecular engineering strategy based on ionic liquid-modified water-based polyurethane (WPU). By introducing ionic liquids as a structural regulator between the WPU chain segments, this strategy purposefully inhibits the excessive aggregation of the hard segments. The resulting material not only exhibits a resistance temperature coefficient (TCR) as high as −2.25% °C −1 , corresponding to a temperature resolution of 0.2 °C, while also possessing excellent anti-mechanical load pressure sensitivity due to the ionic migration−based conductive mechanism. Moreover, by directly coating the thermosensitive layer onto natural silk fibers, a fiber temperature sensor was successfully constructed, with a TCR remaining stable at −2.21% °C −1 , significantly enhancing the wearable and system integration capabilities. This temperature-sensitive material demonstrates outstanding practical value in various application scenarios such as respiratory monitoring, thermal stimulus recognition, touch-based human-computer interaction, and body temperature monitoring. This schematic systematically illustrates the molecular design, device fabrication, and temperature-sensing application logic of ionic-liquid-modified waterborne polyurethane ionogels. The enlarged left panel shows the polymer network with abundant hydrogen-bonding interactions. Based on this material, flexible film sensors can be fabricated, and they can be further extended to fiber sensors via a coating process. The resistance-temperature response curves in the upper right part demonstrate that both types of devices exhibit excellent negative temperature coefficient (NTC) characteristics. The film and fiber sensors achieve TCR values of −2.25% °C −1 and −2.21% °C −1 , respectively. The inset simultaneously verifies their high temperature resolution and robust resistance to pressure interference. The lower right part illustrates that the flexible film/fiber temperature sensors can conformally attach to human skin for real-time body temperature monitoring, highlighting their promising potential in wearable thermosensing applications. Download: Download high-res image (268KB) Download: Download full-size image