Bin Chen,Ming Yuan,Ruixue Ma,Xiaohui Wang,Wei Cao,Chuntai Liu,Changyu Shen,Zhen Wang
Flexible, transparent and lightweight polymer piezoelectric films are promising for emerging sensor applications, including wearable electronics and human–machine interfaces. However, it remains a great challenge for large-scale fabrication of high-quality polymer piezoelectric films by a cost-effective melt processing approach, mainly due to the difficulty of acquiring well-defined electroactive phases. Herein, a readily implementable and scalable strategy is reported to achieve poly(vinylidene fluoride) (PVDF) film with ultrahigh content of electroactive β-phase (∼96%) via melt stretching of slightly crosslinked PVDF. Upon controlled temperature and stretch ratio, the β-phase adopts an oriented nanofibril (diameter, 21.6 nm) morphology, while nanofibrils are further densely and parallelly aligned to fill the film space. The hierarchical nanoscale phase morphology endows the slightly crosslinked film with high optical transmittance (∼90%), good flexibility and also superior mechanical properties. Moreover, flexible piezoelectric device constructed on the film is demonstrated to have excellent electrical output with sensitive and repeatable responses in sensing dynamic pressure (0–250 kPa), temperature variation (3.3 mV o C -1 ), human motions and subtle physiological activities. This study therefore paves the way towards scalable manufacturing of high-performance piezoelectric polymer film through simple melt stretching.
Yian Hu,Shunyao Huang,Yujia Gao,Jaeyeon Lee,Zhangsiyuan Jin,Geon-Hyoung An,Yuljae Cho
Wearable or patchable biosensors have attracted tremendous attention due to their continuous health-monitoring capabilities. In particular, self-powered passive biosensors based on a piezoelectric nanogenerator (PENG) have demonstrated measurements of physiological signals from which cardiovascular information can be analyzed such as heart rate and blood pressure. However, challenges still remain with regard to both material and device aspects. For the effective and accurate measurement of extremely weak physiological signals, various methods have been introduced, including employment of inorganic lead-based piezoelectric materials and design of a complex material or device structure. In spite of their effectiveness in enhancing the piezoelectric output response, the introduced methods brought concomitant issues, such as toxicity and complexity. We present unique methods to produce a transparent standalone piezoelectric polymer film which can be directly transferred to any surface such as the human skin. Through a room temperature solvent vapor annealing process, we further enhance the crystallinity and a portion of the ferroelectric β-phase of the transparent standalone polymer film, resulting in an improved piezoelectric output response. Based on these two new methods introduced, we demonstrate a simple sandwich-structured, transparent, and patchable biosensor based on PENG for radial artery detection with significantly reduced complex manufacturing processes, providing great practical value.
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