Flexible and stretchable stress and strain sensing materials have gained a lot of research interest recently as the development of wearable sensors for health monitoring, motion capturing and soft robotics. In these applications where dynamic stress and strain are common, piezoelectricity becomes a suitable sensing mechanism due to its fast response and high sensitivity. Existing research on flexible piezoelectric materials includes nanocomposites and sandwich composites made of piezoelectric fillers and elastomers. However, the giant modulus mismatch between the two distinct phases makes nanocomposites or sandwich materials prone to inaccurate sensing under large strains due to the weak stress transfer efficiency. In this research, polyvinylidene fluoride (PVDF) and unvulcanized nitrile rubber (NBR) are both dissolved in N,N-dimethylformamide (DMF) and then precipitation printed into a water bath to produce PVDF/NBR polymer blends. The blends are further vulcanized via hot pressing. The resulting blends exhibit polar phases of PVDF, highly uniform blend morphology, as well as excellent stretchability. As a stretchable sensor, the PVDF/NBR (2:8) shows consistent open circuit voltage-strain and open circuit voltage-stress relationships, as well as a high operating strain range up to 70%. Therefore, the PVDF/NBR blend can be used as a promising dynamic stress/strain sensing material for wearable sensors or soft robotic sensors.

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Ruowen Tu and Henry A. Sodano, "Stretchable piezoelectric polymer blend for dynamic stress and strain sensing," Proc. SPIE 12485, Nano-, Bio-, Info-Tech Sensors, and Wearable Systems 2023, 1248502 (Presented at SPIE Smart Structures + Nondestructive Evaluation: March 13, 2023; Published: 18 April 2023); https://doi.org/10.1117/12.2656945.