Abstract
Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm–2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.
Highlights
The need for sustainable energy sources capable of meeting the ever-increasing energy demands of our world has spurred the development of energy-harvesting technologies such as piezoelectrics and triboelectrics.[1]
Piezoelectricity of electrospun polyvinylidene fluoride (PVDF) fibers was often correlated with a high degree of crystallinity, dimensional reduction of fibers, incorporation of additives, nonlinear extrinsic responses, poling, size, and chain orientation parallel to the surface;[28,36,37] we propose that piezoelectricity can be modified with the two often missed parameters in electrospinning: voltage polarity and humidity
We proposed a single-step method to enhance surface chemistry and the piezoelectric performance of electrospun PVDF fibers that can be controlled via voltage polarity and relative humidity during electrospinning
Summary
The need for sustainable energy sources capable of meeting the ever-increasing energy demands of our world has spurred the development of energy-harvesting technologies such as piezoelectrics and triboelectrics.[1]. PVDF combines high piezoelectric, pyroelectric, and ferroelectric properties with high mechanical strength, high thermal stability, and biocompatibility.[7,8] With its unique properties, PVDF has found use in a broad spectrum of applications ranging from biomedical to energy-harvesting systems It was successfully used as a membrane in protein detection systems, an electrolyte in rechargeable cells, part of rewritable memory, a substrate for crystalline ice growth, and cell scaffolds with controlled surface charge.[9−12] PVDF can crystallize in at least four known phases which are related to different chain conformations and these are as follows: trans and gauche (TG+TG−) for α and δ, all-trans (TTTT) for β, and (T3G+T3G−) for γ.7,13,14. Numerous experimental techniques for obtaining high concentrations of the β-phase in PVDF have been investigated including mechanical stretching of polymer films, annealing, exposing to a strong
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