Composites of functionalized multi-walled carbon nanotube and sodium alginate for tactile sensing applications

Flexible tactile sensors are foreseen to be extensively used soon in wearable devices. Various materials in flexible sensor fabrication offer sensing properties with multiple capabilities. The materials, including nanocomposites, have a crucial research area for flexible tactile sensors. While the nanocomposites' electrical properties mainly depend on the nanofillers, the mechanical properties are determined by the polymer component. Carbon nanotubes are one of the most promising materials among nanofillers due to their high electrical conductivity, thermal stability, and durability. However, carbon nanotubes should be processed to increase the binding capacity with the polymer structure. In this study, the nanocomposite used for the sensor manufacturing consists of acid-functionalized carbon nanotubes and sodium alginate as the nanofiller and the polymer material, respectively. The sensors were cross-linked using calcium chloride, and glycerin was involved in the sensor fabrication to check the effect on the sensing and flexibility. Also, it is critical to note that sodium alginate and glycerin are biocompatible and biodegradable substances. On the scope of the study, the impedance changes of the fabricated tactile sensors were examined in the 100 Hz – 10 MHz frequency range and the equivalent circuits of the sensors were created. Besides, the impedance changes were obtained when the alternating forces were applied to the sensors. The results show that the frequency responses of the sensors differ from each other in different frequency ranges. Also, each sensor has different sensing mechanisms in specific frequency ranges, and the sensor, including glycerin, has higher flexibility, but less sensitivity.