Abstract:

Objective In order to promote the development of multi-functional flexible wearable sensors, it is of great significance to develop a sensor which could sense both strain and temperature. PEDOT:PSS is a conductive polymer with excellent thermoelectric properties, and can be employed as an ideal base material for stretchable strain sensor and temperature sensor. In this research, a composite conductive fiber was prepared by wet spinning method to achieve strain and temperature sensing.

Method The composite conductive fibers with different PU content were prepared by the wet spinning method. The conductivity, Seebeck coefficient, power factor and mechanical property of the composite conductive fiber were measured and analyzed. To verify the ability of this fiber as a strain sensor for motion detection, it was fixed on the index finger and wrist respectively, and the resistance response at different bending angles was measured. Furthermore, the fiber was sewn into a glove, and the temperature-sensing performance was studied.

Results With the increase of PU content, the conductive network was destructed by the non-conductive component, resulting in a decrease in conductivity, but the Seebeck coefficient of the composite remained stable because the thermoelectric material was unchanged. The stress and strain of composite fiber were both increased with the increase of PU content. This fiber showed wide work strain range (0%-90%), high sensitivity and good stability. The finger and wrist were bent for 5 times, the maximum resistance changes were basically the same, indicating that the elastic composite wire fiber sensor has good stability. The tensile deformation caused by wrist bending was larger than that caused by finger bending, the corresponding resistance change rate was also much larger than that caused by finger bending. When it is used as a temperature sensor, the voltage is generated by the temperature difference formed at the two ends of the fiber. With the temperature difference increasing, the voltage was increasing too. To detect the water temperature, the fiber was sewn into the glove. Once the hand touches the beaker filled with warm/cold water, a temperature difference was created between the inside and outside of the glove, then a voltage signal was generated. When holding a beaker containing warm water of about 37 ℃, a positive voltage of about 35 μV was generated. After release, the voltage dropped back gradually. When clenched again, the voltage rises at almost the same height. When holding a beaker with ice water at about 0 ℃, a negative voltage of about 50 μV was generated. After release, the voltage returns to 0. When clenched again, a negative voltage of about 45 μV was generated. The result demonstrated that this fiber has great promise for temperature sensing.

Conclusion The conductive PEDOT:PSS/AgNWs/PU fiber was prepared by wet spinning method. The AgNWs were added to improve the conductivity of the composite fiber. The mechanical properties of PEDOT:PSS could be increased by adjusting the ratio of PU. The PEDOT:PSS/AgNWs/PU composite fiber has good mechanical properties, elongation at break can reach 800%, able to detect 0%-90% strain range, and still maintain good stability under 100 cycles of stretching/recovery. In addition, it can also be used as a temperature sensor to quickly detect human body and environmental temperature, showing great potential in health monitoring.

Key words: poly (3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, elastic conductive composite fiber, wet spinning, strain sensor, temperature sensor, smart wearable