Abstract
The technological development of piezoelectric materials is crucial for developing wearable and flexible electromechanical devices. There are many inorganic materials with piezoelectric effects, such as piezoelectric ceramics, aluminum nitride and zinc oxide. They all have very high piezoelectric coefficients and large piezoelectric response ranges. The characteristics of high hardness and low tenacity make inorganic piezoelectric materials unsuitable for flexible devices that require frequent bending. Polyvinylidene fluoride (PVDF) and its derivatives are the most popular materials used in flexible electromechanical devices in recent years and have high flexibility, high sensitivity, high ductility and a certain piezoelectric coefficient. Owing to increasing the piezoelectric coefficient of PVDF, researchers are committed to optimizing PVDF materials and enhancing their polarity by a series of means to further improve their mechanical–electrical conversion efficiency. This paper reviews the latest PVDF-related optimization-based materials, related processing and polarization methods and the applications of these materials in, e.g., wearable functional devices, chemical sensors, biosensors and flexible actuator devices for flexible micro-electromechanical devices. We also discuss the challenges of wearable devices based on flexible piezoelectric polymer, considering where further practical applications could be.
Highlights
Piezoelectric materials have been in development for 140 years [1]
Typical piezoelectric-crystal materials include aluminum nitride (AlN) and zinc oxide (ZnO) [17,18], which have a variety of advantages, such as very high strength, large piezoelectric coefficients and good applicability to micro devices [19,20]
Hosseini et al [92] studied the potential synergistic effect of Cloisite 30B (OMMT) nanoclay and multi-walled carbon nanotube (MWCNT) nanofillers on Polyvinylidene fluoride (PVDF) crystal structure and piezoelectric device performance. They evaluated PVDF fiber mats’ sound-absorbing and piezoelectric properties, and the results show that, compared with OMMT, the MWCNT could decrease PVDF impedance and increase the dielectric constant
Summary
Piezoelectric materials have been in development for 140 years [1]. These materials are widely used in electromechanical devices because they can convert mechanical energy to electrical energy under pressure or generate mechanical motion by electricity [2,3]. Polymer piezoelectric materials have a carbon chain as the backbone, and their flexibility is higher than those of single crystals and ceramics [21,22,23]. This high flexibility allows them to withstand a greater amount of strain, making them more suitable for application scenarios with large bending and twisting requirements. The improvement in the performance of flexible piezoelectric materials has overcome the limitations of wearable electromechanical devices. The applications of these materials in electromechanical devices are discussed in detail. The development trend of flexible electromechanical devices based on PVDF is prospected in the future, such as using the help of piezoelectric properties of biocrystals, improving the biocompatibility for the development of bionic devices
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