Processing of PVDF-based electroactive/ferroelectric films: importance of PMMA and cooling rate from the melt state on the crystallization of PVDF beta-crystals

Abstract

Poly(vinylidene difluoride) (PVDF) displays attractive ferroelectric/piezoelectric properties and its polar β-crystals are specifically targeted for achieving electroactive applications. However, their direct crystallization from the melt state represents a challenging task that has never been addressed using melt-state processes. The use of poly(methyl methacrylate) (PMMA) is herein investigated to promote the PVDF polar β-phase using melt-blending and extrusion-calendering technologies. The presence of the β-phase is here confirmed by ATR-FTIR and WAXS experiments with blends at a PMMA content as low as 5 wt%. The key role of PMMA for the β-phase crystallization from the melt state was unambiguously highlighted with the help of Flash DSC experiments in non-isothermal cooling mode from the melt state. PMMA is able to efficiently shift the α-to-β crystal transition to lower cooling rates (>100-200 °C s-1), making the achievement of the PVDF polar β-phase for these blends compatible with conventional processing tools. A crystal phase diagram is proposed for the PVDF/PMMA blends to highlight the dual effects of both PMMA and cooling rate on the PVDF crystallization during melt-processing. Ferroelectric properties were even observed for the blends containing PMMA up to 10 wt% with the highest remanent polarization obtained at 5 wt% PMMA. After 10 wt% PMMA, a progressive transition from ferroelectric to pseudo-linear dielectric behavior is observed more likely due to the presence of PMMA in the interlamellar amorphous phase of the polar PVDF spherulites as shown by SAXS experiments. In this work, we successfully demonstrated that PMMA plays a key role in the crystallization of PVDF polar crystals from the melt state, enabling large-scale and continuous extrusion processing of PVDF-based materials with attractive dielectric properties for sensing and harvesting applications.

Crystallization kinetics, polymorphism fine tuning, and rigid amorphous fraction of poly(vinylidene fluoride) blends

“…The position of this peak shifts to about 35°C for the 80:20 blend, as seen by Figure 2C. Previous work indicates that these match the melt crystallization of β‐phase 8,32 . As T MC increases, this exothermic peak diminishes and cannot be seen above a certain critical holding time, t MC,C .…”

Ice-templated poly(vinylidene fluoride) ferroelectrets

“…g 33 = 19.9 V m N À1 for the 0.4/10 porous PVDF at 1 kHz compared with g 33 = 0.067 V m N À1 for a ferroelectric porous lead zirconate titanate (PZT) ceramic. 60 In addition, the figures-ofmerit, d 33 2 /e s 33 , for evaluating the performance as an energy harvester were 50 to 4 Â 10 4 (pC N À1 ) 2 , compared with B53 (pC N À1 ) 2 for ferroelectric PVDF 5 and B99 (pC N À1 ) 2 in ferroelectric PZT, 9 leading to interest in ferroelectrets for piezoelectric energy harvesting applications. 1,12,19,20,33,45,51,55 Future avenues can include further optimisation of pore geometry or exploitation of the technique on low dielectric loss porous polymer systems with high permittivity, longer charge and thermal stability, along with energy generation and sensor performance for practical flexible transducer applications.…”

“…4 As a result of a poling process, a dipole-like structure is formed where the dipole moment is changed by the application of a mechanical stress, thereby leading to a piezoelectric response. The piezoelectric d 33 charge coefficient, a measure of the charge generated per unit force, can be an order of magnitude greater than those found in conventional ferroelectric polymers, such as polyvinylidene fluoride (PVDF) and can be comparable or even greater than ferroelectric ceramics [5][6][7] while maintaining a high compliance due to their polymeric nature. For example, for sensor applications a ferroelectret polymer exhibited a sensing figure of merit of d 33 /e s 33 that was 10-150 times higher than a ferroelectric PVDF polymer and over a thousand times higher than a lead zirconate titanate ceramic (PZT), due to its high d 33 values and low permittivity; for example d 33 B 25-700 pC N À1 and e s 33 B 1.12-1.23 for a porous polypropylene based ferroelectret polymer.…”

Improved Design via Simulation of Micro-Modified PVDF and Its Copolymer Energy Harvester with High Electrical Outputs

“…The small-scale feature makes it difficult for such devices to charge the inside battery, therefore self-powering material, which can utilize mechanical energy, such as piezoelectric material, has been given much attention. Taking advantage of the mechanical energy to support small scale devices is possible [ 1 , 2 , 3 , 4 , 5 ]. A great amount of mechanical energy in nature has been wasted, such as airflow, human mechanical motion, and tire scrolling [ 6 , 7 , 8 ].…”