A highly conductive polymer composite with enhanced stretchability and long-term stability for wearable electronic applications

In this study, we investigate the impact of incorporating poly(acrylic acid) (PAA) as a soft polymer on the longterm stability and flexibility (or stretchability) of a highly conductive composite consisting of hydroquinone (HQ)-modified Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (HQ-PEDOT:PSS). Our findings demonstrate that PAA can effectively act as a steric hindrance barrier between conductive-PEDOT and insulativePSS, thus improving the stability of the composite over time. Furthermore, the PAA mixture minimizes the conductivity decrease compared to other representative hydrophilic soft polymers, such as poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP). With the addition of 2 wt% PAA to HQ-PEDOT:PSS, the composite exhibits significantly higher conductivity (290 S/cm) compared to PVA (42 S/cm) and PVP (10-3 S/cm). The HQPEDOT:PSS/PAA composite also displays excellent stretchability, with a sharp strain response followed by a drastically enhanced gauge factor over a wide strain range (10%-50%). As a result, the composite shows great potential as a strain sensor, with high sensitivity for detecting diverse body motions. Moreover, due to its high conductivity, the composite exhibits high sensitivity for detecting human electrocardiogram (ECG) signals, with negligible degradation of signal intensity even one month after fabrication. Overall, our results suggest that the HQ-PEDOT:PSS/PAA conductive composite has significant potential for wearable smart textile applications, enabling diverse body motion and vital sign sensing.