Chitosan-Doped PVDF Film with Enhanced Electroactive β Phase for Piezoelectric Sensing

Polymer-based piezoelectric composites have shown a large potential in various fields of wearable electronics, man–machine interaction, transducers, etc., due to their integrated advantages of high piezoelectric properties, benign flexibility, and pressure sensitivity. As the representative polymer matrix in piezoelectric composites, polyvinylidene fluoride (PVDF) is characterized by its intrinsic piezoelectric response induced via the existence of ferroelectric β and γ phases. However, the most stable phase at ambient temperature and pressure is the nonpolar and paraelectric α phase, which serves as a long-standing issue. Herein, chitosan was introduced into the PVDF matrix to promote the transition from α phase to β phase via the interaction between the –OH and –NH2 groups in chitosan and the H and F atoms in PVDF. As evidenced, the portion of the β phase increased from 47.9 to 63.7%. An electrospinning technique was adopted to prepare PVDF/chitosan composites with a chitosan content ranging from 1 to 4 wt %, and the correlation between structural characteristics and piezoelectric properties is illustrated in detail. Then, a flexible pressure sensor based on PVDF/chitosan composite was prepared, which presents a low detection limit of ∼220 Pa in a wide range of 220 Pa–81 kPa. The pressure sensor presents a good capability for detecting pulse signals and speech recognition accurately. As well demonstrated in this work, the treatment of PVDF with low-cost chitosan may boost its practical application in future flexible electronics.