Enhancing the Polarization and Breakdown Performance of Three-Layer Linear Polymer Films through Modulating the Dielectric Properties of the Inner Layer for Improved Energy Density.

Fabrication, performance and curcumin-controlled release of electrospun sarcoplasmic protein nanofiber films via layer-by-layer self-assembly

Because no known pure biopolymer exhibits all the desired physicochemical properties required for every conceivable packaging application, multilayer films are here proposed as an alternative to improve the performance of protein-based films. In this work, three-layer films based on plasticized wheat gluten films have been developed by applying a more hydrophobic electrospun polyhydroxyalkanoate layers on both sides of the protein film. A commercial polyhydroxybutyrate (PHB) and a polyhydroxybutyrate-co-valerate copolymer with 3 % valerate content (PHBV3) have been used. The morphology, oxygen and water vapour barriers, the optical properties as well as the mechanical performance have been characterized. The effect of film processing temperature (145 and 160 °C) and the amount of electrospun material constituting the outer layers played an important role on the final physicochemical properties of these films. The results showed that water vapour barrier properties were mainly governed, on the one hand, by the deposited amount of the electrospun PHB layer and, on the other hand, by the temperature used for PHBV3-WG-PHBV3 assembly. However, oxygen permeability was greatly influenced by the type and amount of the polyhydroxyalkanoates (PHAs) instead of the temperature used. The lowest water vapour permeability (WVP) and oxygen permeability (OP) values were obtained for three-layer films prepared with 1 mg PHBV3·cm−2 and processed at 160 °C, reaching values of 3.14 ± 0.2 e−11 kg·m·Pa−1·s−1·m−2 and 4.36 ± 0.05 e−15 m3·m·m−2·s−1·Pa−1, respectively. The addition of PHB or PHBV3 outer layers improved the mechanical properties (especially Young’s modulus, which increased up to ~40 % for the three-layer films containing thicker layers) of plasticized wheat gluten films. However, the transparency of the three-layer films was slightly affected by the processing temperature and by the thickness of the outer layer.

Nonstationary dynamics of domain walls in thin multilayer magnetic films with nanosized layers has been investigated using numerical solution of the nonlinear Landau-Lifshitz equation with exact consideration of all major interactions: exchange, magnetoanisotropic, and dipole-dipole (in continuum approximation). Scenarios have been established of nonlinear dynamic transformation of internal wall structure in three-layer films with layers with different saturation magnetization. It has been demonstrated that any velocities of nonstationary motion of the walls (average over the period, maximum over the period, preset at fixed fields) in layered films with the magnetizations of middle layers lower than the magnetization of outer layers are always higher than the velocities of one-layer films of the same thickness with the same average saturation magnetization as in multilayer films.

Multifunctional composites can be achieved by adding two different fillers with complementary properties to a polymer matrix. In this work, novel tri-composite multifunctional materials based on the incorporation of dielectric BaTiO3 (BT) and magnetic CoFe2O4 (CFO) nanoparticles into poly(vinylidene fluoride) (PVDF) have been developed with enhanced dielectric and magnetic responses for applications in areas such as energy harvesting, sensors and actuators. The microstructure, polymer phases as well as the thermal stability of the samples were investigated, showing the independence of the polymer crystallization phases, degree of crystallinity and melting temperature on filler type and contents. Further, independent of the type of the filler, its content improves the degradation temperature of the tri-composites. The magnetic properties and electrical conductivity of the tri-composites are correlated with the increase in the content of the CFO filler, while the dielectric response is mainly determined by the interfacial polarization. A high dielectric constant of 26 at 1 kHz and a magnetization of 5.7 emu * g−1 are obtained for a sample of 10 wt% CFO–10 wt% BT/PVDF, which was used for the demonstration of the suitability of the materials for magnetic deformation sensing. This work provides pathways for the development of tri-composites based on PVDF with high dielectric constant and magnetic properties for application in areas such as sensors and actuators.

High energy storage properties for dielectric composite by asymmetric three-layer films design

The dielectric and thermal properties of three-layer structured films were studied. The two outer layers were about 1 μm and the thickness of the middle layer was varied. We measured the thickness dependence of the dielectric constant of the three-layer structured films. The dielectric results were evaluated with a simple serial three-capacitance model. Local thermal property of these polymer films were also measured using a micro-tip local thermal analysis method. Local glass transition of the film was compared with the one expected from bulk data.

Chemically synthesized gold (Au)-silica nanorods with shell thickness of 0 nm–10 nm were incorporated into the bulk heterojunction of a small-molecule organic solar cell. At optimal (1 wt. %) concentration, Au-silica nanorods with 5 nm shell thickness resulted in the highest power conversion efficiency of 8.29% with 27% relative enhancement. Finite-difference time-domain simulation shows that the localized electric field intensity at the silica shell-organic layer interface decreases with the increase of shell thickness for both 520 nm and 680 nm resonance peaks. The enhanced haze factor for transmission/reflection of the organic layer is not strongly dependent on the shell thickness. Bare Au nanorods yielded the lowest efficiency of 5.4%. Light intensity dependence measurement of the short-circuit current density shows that the silica shell reduces bimolecular recombination at the Au surface. As a result, both localized field intensity and light scattering are involved in efficiency enhancement for an optimized shell thickness of 5 nm.

High energy density and efficiency of laminated polymeric blend-based composites via introducing ultra-low content micrometer sheets

Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications.

Enhancing dielectric property and multi-interface polarization of poly(vinylidene fluoride)/Ni-embedded CaCu3Ti4O12 fibers composites tailored by magnetic field

Dielectric capacitors with an ultrahigh power density have received extensive attention due to their potential applications in advanced electronic devices. However, their inherent low energy density restricts their application for miniaturization and integration of advanced dielectric capacitors. Herein, a novel composite entirely incorporated with two-dimensional (2D) nanosheets with a topological trilayered construction is prepared by a solution casting and hot-pressing method. The 2D boron nitride nanosheets (BNNS) with a wide band gap that are oriented in a poly(vinylidene fluoride) (PVDF) matrix to form the upper and bottom outer layers would efficiently suppress the leakage current in composites, thus significantly improving the overall breakdown strength. Meanwhile, the 2D anatase-type TiO2 nanosheets (TONS) uniformly distributed in the middle layer can enhance their interfacial compatibility and polarization with the PVDF matrix, leading to a synergistic improvement in both the breakdown strength and dielectric constant of the composite. In particular, a significantly improved dielectric constant of ∼11.42, a reduced dielectric loss of 0.03 at 100 Hz, and a maximum discharge energy density (Udis) of 10.17 J cm-3 at an electric field of 370.1 MV m-1 can be obtained from the trilayered composite containing 3 wt % 2D TONS in the middle layer and 2 wt % 2D BNNS on the outer layer. The finding of this research offers an effective strategy for the preparation of advanced polymer-based composites with an outstanding discharge energy density performance.

Flexible pressure sensor based on multi-layer with gradient structure P(VDF-HFP)/MXene/BaTiO3 composite film for human motion monitoring

Understanding the relationship between the fabrication process and the dielectric behavior of thermo‐responsive dielectric materials and accordingly optimizing the dielectric response behavior through simple regulation is critical to advancing their practical applications. For this purpose, we systematically analyze and demonstrate the effects of blow‐spinning process parameters, the feed rate and airflow pressure, on the orientation of poly(vinylidene fluoride) (PVDF) chains, the individual phase fractions of PVDF, the structure of the core‐sheath nanofibers, the mechanical properties, and the dielectric pulsing properties in polyethylene glycol (PEG)‐PVDF core‐sheath fiber films, and achieve the goal of effectively regulating the thermo‐responsive dielectric behavior. In particular, by increasing the airflow pressure, the polar phase fraction of the PVDF can be effectively increased, thus strengthening the dielectric pulsing effect. The significant influence of the processing parameters on the nanofiber structure also allows us to tailor the strength and toughness of the nanofiber films over a wide range by adjusting the feed rate and airflow pressure. Our work shows that the regulation of feed rate and airflow pressure can be used as an effective strategy to optimize the dielectric pulsing and mechanical properties of PEG‐PVDF films, enabling a simple and low‐cost performance optimization of thermo‐responsive dielectric materials.Highlights Effective regulation of thermal dielectric behavior by tuning process parameters. Simple tuning of mechanical properties of nanofiber films over a wide range. High ratio of β‐ and γ‐phases of PVDF by solution blow spinning. Major polar phases contribute to improved mechanical and dielectric properties.

As a functional polymer material, poly(vinylidene fluoride) has attracted broad attention due to its outstanding electroactive properties. The electroactive properties of poly(vinylidene fluoride) depend greatly on its crystalline structure, which in turn depends on the processing conditions. In our recent study, poly(vinylidene fluoride) films were prepared by a solution crystallization method, and the effect of evaporation temperatures on the crystalline phase, crystallinity, and morphology of poly(vinylidene fluoride) was investigated. The results reveal that evaporation temperature is the key factor when studying crystalline structure of poly(vinylidene fluoride). Low temperatures can facilitate the nucleation of β-phase; however, they are disadvantageous for the crystal nucleation and crystal growth. It was also found that the dielectric and ferroelectric properties are closely related to the crystallinity of β-phase of poly(vinylidene fluoride) films. Moreover, the porous structure formed in low evaporation temperatures can lead to a decline in dielectric property and breakdown strength. The films fabricated at 80 °C owned the highest crystallinity of β-phase (49%) and presented the maximum εr (12.5, 103 Hz) and Pr (7 µC/cm2), suggesting that the optimum temperature to prepare poly(vinylidene fluoride) films with excellent electroactive properties is 80 °C.

ABSTRACTBlend of polymers is an effective way to tailor the ferroelectric responses and improve the energy storage properties of polymers. In this work, the microstructure and dielectric responses of the blends of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) [P(VDF‐TrFE‐CFE)] have been studied. It is found that the addition of PVDF disturbs the crystallization process of P(VDF‐TrFE‐CFE), leading to lower crystallinity and smaller crystalline size. The aforementioned microstructure changes result in tailored ferroelectric responses. Dielectric responses show that the blend with 10 wt % PVDF achieves larger polarization response under high electric field (above 300 MV/m) due to the interfacial polarization. Because of the tailoring effect and the interfacial polarization, the blend with 10 wt % PVDF exhibits higher energy density and efficiency. Moreover, the breakdown strength (Eb) is also improved by adding a small amount of PVDF into the terpolymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40994.