A flexible nanofibrous PVDF-BaTiO3 composite material is prepared for impact sensing and biomechanical energy harvesting applications. Dielectric polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3)-PVDF nanofibrous composites were made using the electrospinning process based on a design of experiments approach. The ultrasonication process was optimized using a 2k factorial DoE approach to disperse BaTiO3 particles in PVDF solution in DMF. Scanning electron microscopy was used to characterize the microstructure of the fabricated mesh. The FT-IR and Raman analysis were carried out to investigate the crystal structure of the prepared mesh. Surface morphology contribution to the adhesive property of the composite was explained through contact angle measurements. The capacitance of the prepared PVDF- BaTiO3 nanofibrous mesh was a more than 40% increase over the pure PVDF nanofibers. A comparative study of dielectric relaxation, thermodynamics properties and impact analysis of electrospun polyvinylidene fluoride (PVDF) and 3% BaTiO3-PVDF nanofibrous composite are presented. The frequency dependent dielectric properties revealed micro structural features of the composite material. The dielectric relaxation behavior is further supported by complex impedance analysis and Nyquist plots. The temperature dependence of electric modulus shows Arrhenius type behavior. The observed non-Debye dielectric relaxation in electric loss modulus follows a thermally activated process which can be attributed to a small polaron hopping effect. The particle induced crystallization is supported with thermodynamic properties from differential scanning calorimetric (DSC) measurements. The observed increase in piezoelectric response by impact analysis was attributed to the interfacial interaction between PVDF and BaTiO3. The interfacial polarization between PVDF and BaTiO3 was studied using density functional theory calculations and atomic charge density analysis. The results obtained indicates that electrospinning offers a potential way to produce nanofibers with desired crystalline nature which was not observed in molded samples. In addition, BaTiO3 can be used to increase the capacitance, desired surface characteristics of the PVDF nanofibers which can find potential application as flexible piezoelectric sensor mimicking biological skin for use in impact sensing and energy harvesting applications.

<p dir="ltr">Piezoelectric polymers and ceramics have applications throughout many fields, including their use as pressure sensors and transducers. Of the polymers, poly(vinylidene fluoride – trifluoroethylene) (P(VDF-TrFE)), has been the go-to for its high piezoelectric performance. With the addition of aluminum nanopowders (nAl), P(VDF-TrFE) acts as a binder and oxidizer, creating an energetic composite, a so-called piezoenergetic. However, this typically results in lower d₃₃ coefficients and can have lower reactivity since ideal mixtures may short when poled. Here, we develop and demonstrate single-layer and multilayer polymer composite films with high piezoelectric and energetic content. We prepared single-layer thin film piezoelectric energetic composites of nAl and P(VDF-TrFE) and a combination of thermal annealing and poling at elevated temperatures enabled full poling of 9 wt.% nAl/P(VDF-TrFE) films with d₃₃ of 22.7 pC/N that is comparable to P(VDF-TrFE) films. We also investigated the addition of barium titanate (BaTiO₃) particles as a piezoelectric ceramic to enhance the d₃₃ coefficient. In the neat polymer, BaTiO₃ had differing effects depending on the particle size, with 200 nm particles improving the d₃₃ coefficient more than the 1 μm particles. However, neither size of BaTiO₃ particle had a substantial effect on the piezoelectricity in the 9 wt.% nAl/P(VDF-TrFE) films. We also prepared hot-pressed, three-layer “sandwich” P(VDF-TrFE) – 30 wt.% nAl/P(VDF-TrFE) – P(VDF-TrFE) composites, which had marginally lower d₃₃ coefficients than the single-layer 9 wt.% nAl/P(VDF-TrFE) films. However, the 30 wt.% nAl/P(VDF-TrFE) sandwich films were far more energetic than the 9 wt.% nAl/P(VDF-TrFE) films, as confirmed by simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and deflagration studies. The single films will often fail to fully sustain a deflagration, while the sandwich films burn completely. In addition, we can ignite the sandwich samples with an electrical discharge making these films also useful in ignition applications. To demonstrate the use of piezoenergetic films, 9 wt.% nAl/P(VDF-TrFE) single layer and 30 wt.% nAl/P(VDF-TrFE) sandwich films were calibrated as pressure gauges using a mini drop weight setup, and then demonstrated as a pressure gage. The improvements in the piezoelectric coefficient of the 9 wt.% nAl/P(VDF-TrFE) single layer films, as well as the energetic performance in the form of the 30 wt.% nAl/P(VDF-TrFE) sandwich films strongly amplify the existing potential of these multifunctional composites in energetic and pressure sensing applications.</p>

Zur Messung pyrelektrischer Koeffzienten wurde ein Messplatz nach einem erweiterten SHARP-GARN-Verfahren entwickelt und zur Untersuchung von Phasenumwandlungen in Pyroelektrika eingesetzt. Einerseits konnten pyroelektrische Messungen im elektrischen Feld die Pyroelektrizität einer neuen durch elektrisch angetriebene Defektmigration erzeugten Phase in Strontiumtitanat nachweisen. Andererseits gelang es, Ferroelektrizität in der Hochtemperaturphase von Poly(Vinylidenfluorid-Trifluorethylen), mittels phasenreiner Präparation der Hochtemperaturphase unterhalb der CURIEtemperatur und anschließender Polarisierung, nachzuweisen. Ferner ließen sich mittels thermisch angeregter Pyroelektrika Redoxprozesse antreiben, was durch Desinfektion von Escherichia coli Bakterien in wässriger Lösung mittels Lithiumniobat und -tantalat gezeigt wurde. Die Hypothese der Desinfektion durch reaktive Sauerstoffspezies konnte durch spektroskopisch nachgewiesene OH-Radikale - erzeugt mittels thermisch angeregter Bariumtitanatnanopartikel - belegt werden.