Significantly Enhanced Energy Density of Polyvinylidene Fluoride/Polyimide-Based Nanocomposites by Core-Shell BaTiO3@SiO2.

Improving the limited energy storage capacity of dielectric materials has long been an attractive challenge. In this work, a four-phase hybridized nanocomposite was designed. The linear polymer polyimide (PI) was added to the ferroelectric polymer polyvinylidene fluoride (PVDF) and compounded with a nanoceramic BT@SiO2 with a core-shell structure. The results show that PVDF-PI/BT@SiO2 nanocomposites prepared by a straightforward spin-coating method have a significantly increased discharge energy density. The polymer blends obtain a tightly extended conformation in the amorphous region. Also, this provides an excellent matrix environment for the homogeneous dispersion of fillers. The core-shell structure, as a physical barrier, not only hinders the expansion of the breakdown path but also extends multiple polarization surfaces with gradient variations at the microscopic level. Therefore, the synergistic effect generated by polymer blending and core-shell structure effectively enhances the dielectric and stored energy characteristics of nanocomposites. The dielectric constant is stable at 11.39-18.7, and the dielectric loss is always lower than 0.136. The discharge energy density is 2.5 J/cm3, almost 110% higher than that of the BOPP films (about 1.2 J/cm3). These experimental results suggest that the composite system using core-shell structure and polymer blending is a new way to improve the energy density of dielectric materials.

Electrochemical Performance of Free-Standing and Flexible Graphene and TiO2 Composites with Different Conductive Polymers as Electrodes for Supercapacitors.

The advantage of using composite electrode materials for energy storage is, to a large extent, the synergistic role of their components. Our work focuses on the investigation of the interactions of each phase, exploring the patterns found with the change of materials to provide theoretical or experimental foundations for future study. Here, conductive polymers (CPs), including polyaniline (PANi), polypyrrole (PPy), and polythiophene (PTh), as well as reduced graphene oxide (rGO), and TiO2 with the different crystalline phases of anatase and rutile were applied to form a series of free-standing and flexible binary or ternary composite electrodes. The electrochemical behaviors of these composite electrodes are presented. The results indicate that the synergistic improvement in electrochemical performance is due to the incorporation of the different components. CPs significantly increase the current density of these composite films and contribute their pseudocapacitance to improve the specific capacitance, but lead to a decline in cycle stability. After introducing TiO2 , both the specific capacitance and the cycle-stability of rGO-TiO2 -CP were synergistically improved. A CP can magnify the pseudocapacitance behavior of any of the TiO2 crystalline phases, and interactions vary with the specific CP and the specific TiO2 crystalline phase employed. The synergistic effects of the as-prepared composites were theoretically predicted and explored.

Fabrication of anti-scaling HDPE/fluorinated acrylate polymer/nano-silica composite for landfill leachate piping system.

Clogging generally happens to the leachate piping system, which poses a risk to the environment. A low surface energy nanocomposite is prepared to mitigate the cloggings, by adding the fluorinated acrylate polymer and hydrophobically modified nano-silica into high-density polyethylene (HDPE) substrate. The best addition of the fluorinated acrylate polymer and the nano-silica is given as 15% and 5%, to produce the composite with a low surface energy of 29.4 mJ/m2. Through the characterization of contact angle (CA), electrochemical corrosion, scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), atomic force microscope (AFM) and thermogravimetry (TG), the composite shows low wettability, good corrosion resistance and thermal stability. The surface hydrophobic property of the composite remains unchanged after being immersed in an acidic (pH = 2) and an alkaline (pH = 12) solution, indicating that the prepared composite has strong adaptability to the extreme environments. In addition, the composite shows better anti-scaling performance than that of the commercial high-density polyethylene (HDPE) and polyvinyl chloride (PVC) pipe materials by application of a dispensing leachate immersion test. The results provide insights into engineering practice for the design and manufacture of pipe materials for leachate collection and transport.

Material selection for landfill leachate piping by using a grey target decision-making approach.

Landfill leachate, due to its quantity and inherent risk, is generally collected and transported by piping system for advanced treatment. During the piping, the pipe materials may react with leachate, resulting in corrosion and scaling. In order to reduce possible failures and mitigate the associated consequences, this study provides an indicator system for material selection to aid the pipe system design. The material functional, economic, and environmental attributes are incorporated into the indicator system, to perform a precise selection of commercial drainage pipe materials, thus improving empirically oriented selection. Four common drainage pipe materials including high-density polyethylene (HDPE), polyvinyl chloride (PVC), galvanized steel, and seamless steel are taken as the material alternatives for the selection. Based upon their experimental data, a grey target decision-making framework is employed to perform the priority ranking of the materials. The results indicate that HDPE has the best performance, followed by PVC, galvanized steel, and seamless steel. This study discusses the validity of the selection results and the applicability of the proposed method, to provide insight into  leachate piping system design.

Self-Poled Poly(vinylidene fluoride)/MXene Piezoelectric Energy Harvester with Boosted Power Generation Ability and the Roles of Crystalline Orientation and Polarized Interfaces.

Micropiezoelectric devices have become one of the most competitive candidates for use in self-powered flexible and portable electronic products because of their instant response and mechanic-electric conversion ability. However, achievement of high output performance of micropiezoelectric devices is still a significant and challenging task. In this study, a poly(vinylidene fluoride) (PVDF)/MXene piezoelectric microdevice was fabricated through a microinjection molding process. The synergistic effect of both an intense shear rate (>104 s-1) as well as numerous polar C-F functional groups in MXene flakes promoted the formation of ß-form crystals of PVDF in which the crystallinity of ß-form could reach as high as 59.9%. Moreover, the shear-induced shish-kebab crystal structure with a high orientation degree (fh = ∼0.9) and the stacked MXene acted as the driving force for the dipoles to regularly arrange and produce a self-polarizing effect. Without further polarization, the fabricated piezoelectric microdevices exhibited an open-circuit voltage of 15.2 V and a short-circuit current of 497.3 nA, under optimal conditions (400 mm s-1 and 1 wt % MXene). Impressively, such piezoelectric microdevices can be used for energy storage and for sensing body motion to monitor exercise, and this may have a positive impact on next-generation smart sports equipment.

Scale Deposition Inhibiting Composites by HDPE/Silicified Acrylate Polymer/Nano-Silica for Landfill Leachate Piping.

Scaling commonly occurs at pipe wall during landfill leachate collection and transportation, which may give rise to pipe rupture, thus posing harm to public health and environment. To prevent scaling, this study prepared a low surface energy nanocomposite by incorporating silicone-acrylate polymer and hydrophobically modified nano-SiO2 into the high-density polyethylene (HDPE) substrate. Through the characterization of contact angle, scanning electron microscopy and thermogravimetry, the results showed that the prepared composite has low wettability and surface free energy, excellent thermal stability and acid-base resistance. In addition, the prepared composite was compared with the commercial HDPE pipe material regarding their performance on anti-scaling by using an immersion test that places their samples into a simulated landfill leachate. It was apparent that the prepared composite shows better scaling resistance. The study further expects to provide insight into pipe materials design and manufacture, thus to improve landfill leachate collection and transportation.

Strain sensitivity of band structure and electron mobility in perovskite BaSnO3: first-principles calculation.

A first-principles electronic structure calculation is utilized to contrastively investigate the crystal structure, band structure, electron effective mass and mobility of perovskite BaSnO3 under hydrostatic and biaxial strain. Strain-induced changes in relative properties are remarkable and more sensitive to hydrostatic strain than biaxial strain. The structure of BaSnO3 remains cubic under hydrostatic strain, while it becomes tetragonal under biaxial strain. Originating from the strain sensitivity of the Sn 5s orbitals in the conduction band minimum, the band gaps of BaSnO3 decrease for both types of strain from -3% to 3%. BaSnO3 under tensile hydrostatic strain exhibits higher electron mobility than it does under tensile biaxial strain because of the smaller electron effective mass in the corresponding strain. In contrast, the opposite phenomenon exists in compressive strain. Our results demonstrate that strain could be an alternative way to modify the band gap and electron mobility of BaSnO3.

Improving the Thermoelectric Properties of the Half-Heusler Compound VCoSb by Vanadium Vacancy.

The effects of V vacancy on the thermoelectric performance of the half-Heusler compound VCoSb have been investigated in this study. A certain amount of CoSb secondary phase is generated in the VCoSb matrix when the content of V vacancy is more than 0.1 at%. According to the results, a ZT value of 0.6, together with a power factor of 29 µW cm-1 K-2 at 873 K, were achieved for the nonstoichiometric sample V0.9CoSb. This proved that moderate V vacancy could improve the thermoelectric (TE) properties of VCoSb. The noticeable improvements are mainly owing to the incremental Seebeck coefficient, which may benefit from the optimized carrier concentration. However, too much V vacancy will result in more CoSb impurity and deteriorate the TE performances of VCoSb owing to the increased thermal conductivity.

Preparation and characterization of self-emulsified waterborne nitrocellulose.

Waterborne nitrocellulose (WNC) dispersion was successfully synthesized by self emulsification and reaction among isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA) and nitrocellulose (NC). The WNC was characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and thermal gravimetric analysis (TGA), etc. The WNC dispersion has Z-average particle size of 133 nm approximately and distribution index of 0.152. It is indicated by TEM that the cured WNC particles show a core-shell structure, in which hydrophobic component is encapsulated by the hydrophilic carboxyl. FTIR confirms that the reactions (i.e. IPDI and NC, IPDI and DMPA) have occurred, the - NCO group of IPDI has been consumed totally and the backbone of NC is retained. TGA reveals that the cross-linked WNC film has better thermal resistance, and the water resistance measurement confirms that it has weaker water-sensitivity.