Using “3D-spacer” technology, we have knitted 80% β-phase PVDF with Ag/PA66 fibres to demonstrate all fibre piezoelectric power generators. The 3D structure provides a power density of 1.10–5.10 μW cm−2 at applied impacts of 0.02–0.10 MPa.
Keywords: PVDF, piezoelectric effect, self-alignment, β-phase, Piezo Force Microscopy Poly(vinylidene fluoride), (PVDF), is one of the most attractive polymers owing to its remarkable pyro-, piezo-and ferro-electroactive properties. [1][2][3][4] These properties stem from its unique polymorphism which also gives rise to its extraordinary mechanical properties, high chemical resistance, good thermal stability and biocompatibility. [5] PVDF shows four significant crystalline phases α, β, δ and γ; [2,6] with the electroactive β-phase being utilized most frequently for the development of sensors, actuators [7,8] and microgenerators. [4,9,10] Owing to its importance, the formation of electroactive β crystalline phase has been intensively investigated through various routes, including melt casting, [15] solution deposition, [11] spin coating [12] and phase inversion. [13,14] While, the films or membranes formed by 2 melting/crystallisation are dominated by α-phase, [15] those obtained by spin-coating and further dried at temperature between 30-60 ºC are largely dominated by β-phase crystals. [12] For the phase inversion technique, PVDF films are formed by quenching the casting films into a nonsolvent bath to induce a series of liquid-solid and liquid-liquid phase separation events. [5,13,14] The microstructure and crystalline phase of the polymer films in phase-inversion can be controlled by adjusting paramteres like composition, [5,12] type of solvent, [16,17] quenching temperature etc. [18,19] Although PVDF films formed by this technique can have high β-phase contents, they are mostly porous and not suitable for electroactive applications. Moreover, the β-phase crystals are randomly oriented in these PVDF films and show no specific directional preference. Polarization under high electric field, [6,20] by Corona poling, [12] or by mechanical stretching [3,6,15] is subsequently carried out to obtain electroactive PVDF films. These operations need to be done at elevated temperatures (>80 o C), requiring high voltage equipment and films with dense structure and high β-phase content. Spontaneous formation of electroactive -phase in PVDF nanofibers formed by drawing was reported to have piezoelectric coefficient up to d33=58.5 pm/V. [25] Similarly, PVDF mesoscale rod arrays, without any poling process, too were also reported to possess good piezoelectric properties due to their high β content. [24] In both these cases, mechanical stretching and stress during the template guiding are believed to be responsible for the piezoelectric effect. Self-polarization of oriented β-phase crystals has also been observed in ultrathin (~20 nm) PVDF copolymer films by spin-coating or by Langmuir-Blodgett (LB) method, and is attributed to the built-in electric field, in-film stress and the strong interaction of PVDF molecules with polar water. [21,22,23] Generally speaking, PVDF films or membrane formed by melt casting, solution deposition, spin coating and phase inversion etc. do not exhibit aligned β-phase crystals without additional t...
Piezoelectric materials have been in use for many years; however, with an increasing concern about global warming, piezoelectricity has gained significant importance in research and development for extracting energy from the environment. In this work the voltage responses of ceramic based piezoelectric fibre composite structures (PFCs) and polymer based piezoelectric strips, PVDF (polyvinylidene fluoride), were evaluated when subjected to various wind speeds and water droplets in order to investigate the possibility of energy generation from these two natural renewable energy sources for utilization in low power electronic devices. The effects of material dimensions, drop mass, releasing height of the drops and wind speed on the voltage output were studied and the power was calculated. This work showed that piezoelectric polymer materials can generate higher voltage/power than ceramic based piezoelectric materials and it was proved that producing energy from renewable sources such as rain drops and wind is possible by using piezoelectric polymer materials.
Vertical contact-separation mode triboelectric generator (TEG) based on lead-free perovskite, zinc stannate (ZnSnO 3 )-polyvinylidene fluoride (PVDF) composite and polyamide-6 (PA6) membrane is demonstrated. For the 5wt% PVDF-ZnSnO 3 nanocomposites, the facile phaseinversion method provides a simple route to achieve high crystallinity and β-phase with a piezoelectric coefficient d 33 of -65 pmV -1 , as compared to -44 pmV -1 for pristine PVDF membranes. Consequently, at a cyclic excitation impact of 490 N/3 Hz, the PVDF-ZnSnO 3 /PA6 based TEGs provide a significantly higher voltage of 520 V and a current © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 density of 2.7 mAm -2 (corresponding charge density of 62.0 µCm -2 ), as compared to the pristine PVDF-PA6 TEG which provides up to 300 V with a current density of 0.91 mAm -2(corresponding to a charge density of 55.0 µCm -2 ). This increase in the electrical output can be attributed to not only the enhanced polarisation of PVDF by ZnSnO 3 leading to an increase in the β-phase content, but also to the surface charge density increase by stress induced polarisation of ZnSnO 3 , leading to the generation of stronger piezoelectric potential.The work thus introduces a novel method of enhancing the surface charge density via the addition of suitable high polarization piezoelectric materials thus eliminating the need for prior charge injection for fluoropolymer membranes.
Rapid technological advances in nanotechnology, microelectronic sensors and systems are becoming increasingly miniaturized to the point where embedded wearable applications are beginning to emerge. A restriction to the widespread application of these microsystems is the power supply of relatively sizable dimensions, weight, and limited lifespan. Emerging micropower sources exploit self-powered generators utilizing the intrinsic energy conversion characteristics of smart materials. 'Energy harvesting' describes the process by which energy is extracted from the environment, converted and stored. Piezoelectric materials have been used to convert mechanical into electrical energy through their inherent piezoelectric effect. This paper focuses on the development of a micropower generator using microcomposite based piezoelectric materials for energy reclamation in glove structures. Devices consist of piezoelectric fibres, 90-250 μm in diameter, aligned in a unidirectional manner and incorporated into a composite structure. The fibres are laid within a single laminate structure with copper interdigitated electrodes assembled on both sides, forming a thin film device. Performances of devices with different fibre diameters and material thicknesses are investigated. Experiments are outlined that detail the performance characteristics of such piezoelectric fibre laminates. Results presented show voltage outputs up to 6 V which is considered enough for potential applications in powering wearable microsystems.
Polymers have been widely used as piezoelectric materials in the form of films and bulk materials but there are limited publications on piezoelectric fibre structures. In this paper the process of preparing piezoelectric polyvinylidene fluoride (PVDF) fibres from granules by continuous melt extrusion and in-line poling is reported for the first time. The poling of PVDF fibres was carried out at an extension ratio of 4:1, a temperature of 80 •C and a high voltage of the order of 13 000 V on a 0.5 mm diameter fibre in a melt extruder. The entire process of making PVDF fibres from granules and poling them to make piezoelectric fibres was carried out in a continuous process using a customized melt extruder. The prepared piezoelectric fibres were then tested using an impact test rig to show the generation of voltage upon application of an impact load. PVDF granules, unpoled fibres and poled fibres were examined by Fourier transform infrared spectroscopy (FTIR) which showed the presence of β phase in the poled fibres. The ultimate tensile stress and strain, Young's modulus and microstructures of poled and unpoled fibres were investigated using a scanning electron microscope (SEM). Abstract. Polymers have been widely used as piezoelectric materials in the form of films and bulk materials but there are limited publications on piezoelectric fibre structures. In this paper the process of preparing piezoelectric Polyvinylidene Fluoride (PVDF) fibres from granules by continuous melt extrusion and in-line poling is reported for the first time. The poling of PVDF fibres was carried at an extension ratio of 4:1, temperature of 80 °C and high voltage of the order of 13000 V on a 0.5mm diameter fibre in a melt extruder. The entire process of making PVDF fibres from granules and poling them to make piezoelectric fibres was carried out in a continuous process using a customised melt extruder. The prepared piezoelectric fibres were then tested using an impact test rig to show the generation of voltage upon application of an impact load. PVDF granules, unpoled fibres and poled fibres were examined by Fourier Transform Infrared Spectroscopy (FTIR) which shows the presence of β phase in the poled fibres. The ultimate tensile stress and strain, Young's modulus and microstructures of poled and unpoled fibres were investigated using a scanning electron microscope (SEM).
The preparation of nitrogenated carbon nanotubes (N-CNT) using pyridine as a carbon precursor resulted in an eight-times increase in gravimetric capacitance.
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