Our sensor could provide fast and stable attainment of sensitivity and long-term stability as an optimal humidity sensor. The CNT@CPM sensors were immobilized on a flexible sensor that could provide good contact with the skin or wearable devices. However, the development of wearable electronics requires long-term and mechanical stability characteristics that require sensor reliability and durability under harsh conditions. The long-term stability results of CNT@CPM-3 showed few resistance changes for each relative humidity over a period of over 1 month (Fig. 5a), indicating that it remains a stable sensor over a long duration at 50, 70, and 90%RH. Different proportions of sensors (CNT@CPM) showed the same long-term stability results and unchanged morphologies (Additional file 1: Fig. S18, S19). The mechanical properties of the flexible sensor were evaluated by monitoring their responses under different bending angles (Fig. 5b). The resistance of the device did not change even after bending at 180. Additionally, there was no change in resistance after 15,000 bending cycles, demonstrating the superior flexibility and durability of the sensor (Fig. 5c, Additional file 1: Fig. S19, S20). The RH response to humidity changes was evaluated over 15,000 bending cycles as well. These results demonstrated that the response was nearly unchanged even when the device was bent up to 180 over 15,000 bending cycles, which indicates the excellent mechanical durability, stability, and robustness of the CNT@CPM based humidity sensor. When bending was performed about 18,000 times, CNT@CPM was detached, which is a result of bending in a harsher condition than the actual condition. Therefore, the sensor can be effectively applied to practical applications such as skin-attachable or wearable devices. It is clear that the humidity detection performance of the flexible sensors remained almost constant within experimental errors at different bending numbers and angles, demonstrating their potential as a promising flexible wearable sensing device [39]. More interestingly, the sensor can also respond to other volatile polar organic molecules (chloroform, acetone, ethanol, methanol, dichloromethane, tetrahydrofuran, acetic acid, and ammonia) through resistance changes in a different manner, indicating its great potential for application in organic molecule sensing (Fig. 5d).
Resistance Flexibility 1.0: Becoming Flexible In All Ways... Download Pdfl
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