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The pressure establishment in the solid conveying section of a vane extruder was theoretically and experimentally studied in the present article. Based on the structural and conveying characteristics of the vane extruder, a four‐plate model was developed. The effects of the device geometry (eccentricity ε and discharge port β), the polymer properties (different materials), and the operating conditions (temperature and rotating speed) on the pressure were also studied using a visual experimental device. The results showed that the experimental data were highly consistent with the theoretical data, which indicated that the theoretical model was sensible. Considering the optimization design of the device and its processing parameters, the eccentricity ε and the discharge port β of the discharge baffle should be appropriately selected, and the setting temperature of the feeding section should be set to a low value. The rotating speed of the rotor had no significant influence on the pressure establishment. In addition, the thermo‐mechanical history of the vane extruder was shorter than that of the conventional screw extruder. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

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Triboelectric polymer with high charge density is the foundation to promote the wide range of applications of triboelectric nanogenerators. This work develops a method to produce triboelectric polymer based on repeated rheological forging. The fluorinated ethylene propylene film fabricated by repeated forging method not only has excellent mechanical properties and good transmittance, but also can maintain an ultrahigh tribo-charge density. Based on the film with a thickness of 30 μm, the output charge density from contact-separation nanogenerator reaches 352 μC·m−2. Then, the same film is applied for the nanogenerator with air-breakdown mode and a charge density of 510 μC·m−2 is further achieved. The repeated forging method can effectively regulate the composition of surface functional groups, the crystallinity, and the dielectric constants of the fluorinated ethylene propylene, leading to the superior capability of triboelectrification. Finally, we summarize the key parameters for elevating the electrification performance on the basis of molecular structure and related fabrication crafts, which can guide the further development of triboelectric polymers.

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Although electrostriction is ubiquitous for dielectric polymers, giant electrostriction has not been observed until relaxor ferroelectric (RFE) poly­(vinylidene fluoride) (PVDF)-based polymers are achieved. However, the exact origin for giant electrostriction in these polymers has not been fully understood. By studying the electrostriction in the uniaxially stretched films of a ferroelectric poly­(VDF-co-trifluoroethylene) [P­(VDF-TrFE)] random copolymer and an RFE poly­(VDF-co-TrFE-co-chlorotrifluoroethylene) [P­(VDF-TrFE-CTFE)] random terpolymer in this work, we confirmed that ferroelectric switching with large hysteresis, such as in the case of P­(VDF-TrFE), was not genuine electrostriction. By decreasing large ferroelectric domains to the nanometer scale (i.e., 2–3 nm), such as in the case of the P­(VDF-TrFE-CTFE) terpolymer, electrostriction with low hysteresis could be achieved. Two origins of the large electrostriction in these polymers were identified. The first was the mechano-electrostriction due to the poling field-induced conformation transformation of oriented polymer chains. The second was the electric repulsion of electrically aligned nanodomains. These effects could occur in both crystals and the oriented amorphous fraction, which links between the nanocrystals and the isotropic amorphous fraction. When the poling field was relatively low (e.g., <40 MV/m), the mechano-electrostriction was the major contribution and the electric repulsion effect was a minor contribution to electrostriction. Meanwhile, a strong temperature dependence of the low-field electrostriction coefficient was observed. Finally, we found an empirical inverse relationship between the electrostriction coefficient and the product of Young’s modulus and dielectric constant. The knowledge obtained from this study provides an insightful understanding of the electrostriction mechanism in PVDF-based electroactive polymers, which will find potential applications in sensors and actuators for wearable electronics and soft robotics.

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