Cooling rate controlled microstructure evolution through flash DSC and enhanced energy density in P(VDF-CTFE) for capacitor application

High-performance sono-piezoelectric nanocomposites enhanced by interfacial coupling effects for implantable nanogenerators and actuators

Transcutaneous energy-harvesting technology based on ultrasound-driven piezoelectric nanogenerators is the most promising technology in medical and industrial applications. Based on ultrasonic coupling effects at the interfaces, the interfacial architecture is a critical parameter to attain desirable electromechanical properties of nanocomposites. Herein, we successfully synthesized core-conductive shell-structured BaTiO3@Carbon [BT@Carbon] nanoparticles [NPs] as nanofillers to design implantable poly(vinylidenefluoride-co-chlorotrifluoroethylene)/BT@Carbon [P(VDF-CTFE)/BT@Carbon] piezoelectric nanogenerators (PENGs) and actuators for harvesting ultrasound (US) underneath the skin. For US-driven PENGs, the electrons and holes are generated not only from the interfaces between the BT@Carbon NPs and the matrix, but also from the dipoles vibrating in the smaller lamellae of ferroelectric β-phase crystals in poled nanocomposites. Remarkably, P(VDF-CTFE)/BT@Carbon piezoelectric nanogenerators could attain an extraordinary output power of 521 μW cm-2 under ultrasound stimulation, which is far greater than that of force-induced PVDF-based nanogenerators and other ultrasound-driven triboelectric generators. Furthermore, the US-PENG actuator system, which is composed of an amplifier and a microcontroller, could efficiently convert ultrasonic energy into electricity or instructions to switch on/off small electronics in the tissues and organs of mice. Finally, the nanocomposite-based US-driven PENGs have a good biocompatibility, with no cytotoxicity or immune response in vivo, indicating their potential for developing wireless power generators and actuators for medical implant devices.

Progress on Polymer Dielectrics for Electrostatic Capacitors Application

Polymer dielectrics are attracting increasing attention for electrical energy storage owing to their advantages of mechanical flexibility, corrosion resistance, facile processability, light weight, great reliability, and high operating voltages. However, the dielectric constants of most dielectric polymers are less than 10, which results in low energy densities and limits their applications in electrostatic capacitors for advanced electronics and electrical power systems. Therefore, intensive efforts have been placed on the development of high-energy-density polymer dielectrics. In this perspective, the most recent results on the all-organic polymer dielectrics are summarized, including molecular structure design, polymer blends, and layered structured polymers. The challenges in the field and suggestions for future research on high-energy-density polymer dielectrics are also presented.

Characteristics of the Non-Isothermal and Isothermal Crystallization for the β Polymorph in PVDF by Fast Scanning Calorimetry

Structuring at very high rates has become one of the current and important topics of interest in polymer science, because this is a common protocol in the processing of films or fibers with industrial applicability. This work presents the study by fast scanning calorimetry, FSC, of poly(vinylidene fluoride), paying special attention to the conditions for obtaining the β phase of this polymer, because it is the one technologically more interesting. The results indicate that this β phase of poly(vinylidene fluoride) is obtained when the sample is isothermally crystallized at temperatures below 60 °C. Under non-isothermal conditions, the β polymorph begins to be observed at rates above 400 °C/s, although a coexistence with the α modification is observed, so that exclusively the β phase is obtained only at rates higher than 3000 °C/s.

Effect of Dielectric Barrier Discharge (DBD) Treatment on the Dielectric Properties of Poly(vinylidene fluoride)(PVDF)-Based Copolymer

Understanding the mechanism of dielectric breakdown is important for improving the breakdown field of a polymer. In this work, dielectric barrier discharge (DBD) treatment was applied to one surface of P(VDF-CTFE) (vinylidene fluoride-chlorotrifluoroethylene) film, and the dielectric properties of the film were studied. When the treated surface was connected to the high potential side of the power source for the breakdown test, the breakdown field of the treated film was significantly reduced compared to that of the pristine film. Based on the characterization results for the surface chemistry and morphology, it was proposed that the phenomenon was caused by the combined effects of hole injection from the metal electrode and the damage of polymer chains near the surface of the polymer film after the DBD treatment process.

In-depth understanding of interfacial crystallization via Flash DSC and enhanced energy storage density in ferroelectric P(VDF-CTFE)/Au NRs nanocomposites for capacitor application

High-capacity or high-power-density capacitors are being actively investigated for portable electronics, electric vehicles, and electric power systems. We describe the filler system in dielectric nanocomposites with a small loading of Au nanorods [NRs] to elucidate the mechanism of interfacial crystallization behavior including the crystallization kinetics, and crystalline morphology and structure, and to investigate the intrinsic causes for concurrent great improvements in the dielectric constant and energy density in the nanocomposite system. Remarkly, at high crystallization temperature, the addition of Au NRs, which are used as heterogeneous nucleators, can reduce the nucleation barrier, resulting in accelerating the crystallization rate. However, the crystallization rate slows down at low temperatures because the addition of Au NRs limited the mobility of poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] chains, and thus enhanced the diffusion barrier. Furthermore, the addition of NRs has a huge impact on the crystalline morphology and structure which changes from large paraelectric α-phase spherulites with TGTG' conformations into minor ferroelectric γ-phase spherulites with T3GT3G' conformations, and also produces more exogenous interfaces between the lamellar crystals and amorphous regions, resulting in a higher dielectric constant and higher electric energy density in P(VDF-CTFE)/Au NRs nanocomposites. Our approach provides a facile and straightforward way to design or understand PVDF-based polymers for their practical applications in high-energy-density capacitors.