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.

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