Poly(vinylidene fluoride) (PVDF) displays ferroelectric, piezoelectric and pyroelectric behavior and it is widely used in high-tech applications including sensors, transducers, energy harvesting devices and actuators. The crystallization of this polymer into highly polar  phase is desirable but is hard to achieve without applying specific thermo-mechanical treatments. Indeed, fabrication processes directly affect PVDF molecular chain conformation, inducing distinct polymorphs. In this paper, we present the fabrication of PVDF/BaTiO3 composite foams by thermally induced phase separation method (TIPS). Different compositions are tested and characterized. The crystallinity, and in particular the development of electroactive  crystal phase is monitored by FTIR, DSC and XRD measurements. Dielectric properties are also evaluated. It turns out that TIPS is a straightforward method that clearly promotes the spontaneous growth of the  phase in PVDF and its composite foams, without the need to apply additional treatments, and also significantly improves the degree of crystallinity. BaTiO3 content gives additional value to the development of  phase and total crystallinity of the systems. The low permittivity values (between 2 and 3), combined with the cellular morphology makes these materials suitable as lightweight components of microelectronic circuits.

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This paper deals with the optimization of the piezoelectric performances of nanofibrous membranes. Both ceramic and polymeric piezoelectric nanofibers are manufactured via electrospinning and polarized in order to align the ferroelectric domains and enhance the piezoelectric response of the mats. By investigating the electrical properties of the embedding mediums where the nanofibers were immerged during the polarization, it is possible to identify a proper configuration that maximize the dipoles alignment. The measured piezoelectric responses of the produced nanofibrous mats result comparable with commercial stiff piezoelectric samples ones.

Cross-linking of poly(vinyl alcohol) (PVA) creates a three-dimensional network by bonding adjacent polymer chains. The cross-linked structure, upon immersion in water, turns into a hydrogel, which exhibits unique absorption properties due to the presence of hydrophilic groups within the PVA polymer chains and, simultaneously, ceases to be soluble in water. The properties of PVA can be adjusted by chemical modification or blending with other substances, such as polymers, e.g., conductive poly[3-(potassium-5-butanoate)thiophene-2,5-diyl] (P3KBT). In this work, PVA-based conductive semi-interpenetrating polymer networks (semi-IPNs) are successfully fabricated. The systems are obtained as a result of electrospinning of PVA/P3KBT precursor solutions with different polymer concentrations and then cross-linking using “green”, environmentally safe methods. One approach consists of thermal treatment (H), while the second approach combines stabilization with ethanol and heating (E). The comprehensive characterization allows to evaluate the correlation between the cross-linking methods and properties of nanofibrous hydrogels. While both methods are successful, the cross-linking density is higher in the thermally cross-linked samples, resulting in lower conductivity and swelling ratio compared to the E-treated samples. Moreover, the H-cross-linked systems have better mechanical propertieslower stiffness and greater tensile strength. All the tested systems are biocompatible, and interestingly, due to the presence of P3KBT, they show photoresponsivity to solar radiation generated by the simulator. The results indicate that both methods of PVA cross-linking are highly effective and can be applied to a specific system depending on the target, e.g., biomedical or electronic applications.

Piezoelectric (PE) materials play an important role in the emerging field of micro and wearable electronics. Achieving high PE response is a key feature for their use in energy harvesting and sensing systems. In this study, highly porous lightweight composite foams composed of PVDF‐TrFE (70/30 and 80/20 mol%) and different BaTiO3 content (5, 10, and 20 wt%) are prepared by thermally induced phase separation method. The PE foams were structurally and thermally examined by using Fourier‐transform infrared spectroscopy, x‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis analyses. All composite foams were characterized by high β‐phase content, while the addition of ceramic particles resulted in higher crystallinity and thermal stability of the investigated foams. Two distinct poling methods were employed due to the different molar compositions of the copolymers. The PE response was measured by the PE strain coefficient (d33) and the output current (Ip). The composite foams based on PVDF‐TrFE 70/30 mol% copolymer, having two well‐separated Curie temperatures for the organic and inorganic phases, can be polarized to achieve the contribution of both components to the PE performance, reaching the highest value of −28.3 pC N−1 and 130 nA at 10 Hz for the composite with 20 wt% BaTiO3.