Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d
| < 30 pC/N. We prepare a highly piezoelectric polymer (d
= -62 pC/N) ...based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals are achieved, which show a high spontaneous polarization (P
) of 140 mC/m
. Given the theoretical limit of P
= 188 mC/m
for the neat β crystal, the high P
cannot be explained by the crystalline-amorphous two-phase model (i.e., P
= 270 mC/m
). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d
for the poled BOPVDF. The plausibility of this conclusion is supported by molecular dynamics simulations.
•This review introduces the molding method of multi-dimensional cellulose materials.•The current scenario of the preparation method of cellulose/carbon composites is summarized.•Applications of ...cellulose/carbon composites in environmental protection are described.•The progress and future potential of composites in water treatment are discussed.
Cellulose, as the most abundant natural polymer material on the earth, has attracted worldwide attention due to its characteristics of reproducibility, universality, low cost, biocompatibility and biodegradability. Cellulose-based materials have potential value in supercapacitors, environment and biomedicine. The combination of cellulose and carbon materials can further adjust the microstructure of the composite such as porosity (76–98.8%) and specific surface area (5.07–47.3 m2/g), and enhance the properties of the composite such as the adsorption rate (47–100%) and the degradation rate of pollutants (60–100%), the Young's modulus (1.14–16.6 GPa) and the tensile strength (23.1–277.5 MPa). Besides, composites have the advantages of high electronic transmission efficiency and good reusability, which broaden their applications in water treatment. This review summarizes the molding methods of multi-dimensional cellulose materials, as well as the development status, preparation and modification methods of composites formed by carbon materials such as graphene, carbon nanotubes, activated carbon and nanodiamonds with cellulose, analyzes the research progress and existing problems of the composites in water treatment fields such as adsorption, catalysis, membrane separation and microbial fuel cells, and finally, we make some perspectives for the future researches and applications.
Superhydrophobic electromagnetic interference (EMI) shielding textile (EMIST) is of great significance to the safety and long-term service of all-weather outdoor equipment. However, it is still ...challenging to achieve long-term durability and stability under external mechanical deformations or other harsh service conditions. Herein, by designing and implementing silver nanowire (AgNW) networks and a superhydrophobic coating onto a commercial textile, we demonstrate a highly robust superhydrophobic EMIST. The resultant EMIST shows a synergy of high water contact angle (160.8°), low sliding angle (2.9°), and superior EMI shielding effectiveness (51.5 dB). Remarkably, the EMIST still maintains its superhydrophobic feature and high EMI shielding level (42.6 dB) even after 5000 stretching-releasing cycles. Moreover, the EMIST exhibits strong resistance to ultrasonic treatment up to 60 min, peeling test up to 100 cycles, strong acidic/alkaline solutions, and different organic solvents, indicating its outstanding mechanical robustness and chemical durability. These attractive features of the EMIST are mainly a result of the joint action of AgNWs, carbon nanotubes, polytetrafluoroethylene nanoparticles, and fluoroacrylic polymer. This work offers a promising approach for the design of future durable, superhydrophobic EMISTs, which are capable of remaining fully functional against long-time exposure to extreme conditions, for example, wet and corrosive environments.
Polylactide (PLA) films with an excellent balance of toughness and stiffness were realized by extensional stress efficiently. For the relatively low extensional stress, gauche–gauche conformers that ...originated from the oriented amorphous chains lead to super-toughening behavior. Among higher extensional stress, strain-induced orientation and crystallization act as the driving force of reinforcement. This mechanism is evidenced by the pronounced enhancement in the elongation at break from 16.9 up to 294.9% accompanying the variation yield strength from 45.3 up to 135.5 MPa. The highest elongation at break results from the early stretching stages, whereas the highest yield strength is obtained from a high draw ratio. More impressively, PLA films show temperature-invariant super-ductility and reinforcement at low temperatures (0 and −20 °C). This work provides a preferable and scalable method to fabricate competitive PLA materials, expanding the practical application of sustainable polymers served at a wide temperature range or in harsh environments.
Polymer processing is an essential step in achieving the desired shape and properties of polymer parts that are being broadly used in areas from packaging to aerospace. However, the design of the ...processing for new products is a matter of trial and error in practice. This is partly due to a limited understanding of polymer crystallization under realistic processing conditions, where strong shear flow and elevated pressure are coupled in an inhomogeneous manner. Unlike the well-established research topics that focus on polymer crystallization under the sole effect of pressure or shear flow, the subject of this Perspective is crystallization under processing conditions which include both, i.e., flow-induced crystallization under pressure (FICP). Here we focus particularly on recent advances in this field. Starting with a brief introduction of the special experimental devices for studying FICP, we discuss the remarkable interplay between flow and pressure and its effect on crystallization kinetics, crystal structure, and morphology. Accelerated crystallization, multiphase diagrams, and newfound crystalline morphologies may enrich the theory of polymer crystallization and require its further development. We then summarize the in situ studies of polymer crystallization under realistic processing conditions based on state-of-the-art characterization systems. This is followed by an overview of “structuring” polymer processing methods based on the theoretical understanding of FICP. The paper concludes with an assessment of the prospective future research directions.
Highlights
A multi-scale conductive network was constructed in flexible PDMS/Ag@PLASF/CNT composite with micro-size Ag@PLASF and nano-size CNT.
The PDMS/Ag@PLASF/CNT composite showed outstanding ...electrical conductivity of 440 S m
-1
and superior electromagnetic interference shielding effectiveness of up to 113 dB.
The PDMS/Ag@PLASF/CNT composites owned good retention (> 90%) of electromagnetic interference shielding performance even after subjected to a simulated aging strategy or 10,000 bending-releasing cycles.
Highly conductive polymer composites (CPCs) with excellent mechanical flexibility are ideal materials for designing excellent electromagnetic interference (EMI) shielding materials, which can be used for the electromagnetic interference protection of flexible electronic devices. It is extremely urgent to fabricate ultra-strong EMI shielding CPCs with efficient conductive networks. In this paper, a novel silver-plated polylactide short fiber (Ag@PLASF, AAF) was fabricated and was integrated with carbon nanotubes (CNT) to construct a multi-scale conductive network in polydimethylsiloxane (PDMS) matrix. The multi-scale conductive network endowed the flexible PDMS/AAF/CNT composite with excellent electrical conductivity of 440 S m
−1
and ultra-strong EMI shielding effectiveness (EMI SE) of up to 113 dB, containing only 5.0 vol% of AAF and 3.0 vol% of CNT (11.1wt% conductive filler content). Due to its excellent flexibility, the composite still showed 94% and 90% retention rates of EMI SE even after subjected to a simulated aging strategy (60 °C for 7 days) and 10,000 bending-releasing cycles. This strategy provides an important guidance for designing excellent EMI shielding materials to protect the workspace, environment and sensitive circuits against radiation for flexible electronic devices.
Currently, many catalysts are inconvenient to separate from water, and the solvents used in the preparation process are not environmentally friendly, resulting in low recovery efficiency and ...secondary pollution. In this study, the magnetic and porous regenerated cellulose/carbon nanotubes/Fe3O4 nanoparticles (RC/CNTs/Fe3O4 NPs) composites were synthesized for activation of peroxydisulfate (PDS) in a green alkaline-urea system. The RC/CNTs/Fe3O4 NPs-PDS system achieved 100% removal of bisphenol A compared with CNTs (~64.6%), RC (~0%) or Fe3O4 NPs (~0%), which was closely related to the introduction of defects and functional groups, nitrogen doping and conductive networks. Interestingly, the strong interaction between CNTs and the sheath-like protective layer formed by urea on the cellulose surface promotes the introduction of nitrogen into the composites at the preparation temperature of 70 °C. Moreover, the mechanism of the system was found to be a typical non-radical pathway. Fortunately, there is no leaching of iron ions in the system, and the effects of the actual waterbody, initial pH, and different anions are negligible. The recycling and separation experiments revealed the practicality and superiority of the composite. This work provides a feasible and sustainable strategy for the application of natural cellulose-supported catalysts.
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•Porous RC/CNTs/Fe3O4 NPs were prepared using natural cellulose as a support.•The catalyst exhibited excellent performance for activating PDS.•The enhanced activity stems from the synergistic effect of cellulose and CNTs.•A way of doping nitrogen with a temperature of 70 °C was discovered.•The non-radical mechanism of RC/CNTs/Fe3O4 NPs-PDS system was proposed.
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•A dual neural network architecture is proposed to predict different types of stress–strain curves.•This model is featured by the state-of-the-art simplicity of 300 neurons in ...total.•Such simplicity allows the model to utilize a very small dataset of 27 samplings from a 4D space.•This model is easily interpreted to gain physics insights into the mechanical behaviors.
Predicting stress–strain curves is key to facilitate the design of polymer materials and their products with tailored mechanical response. However, due to their structural complexity, polymeric solids generally feature complex stress–strain curves, which renders it challenging to model their stress–strain behaviors. Here, using the categorized knowledge of stress–strain curves, a “Classification-Embedded Dual Neural Network (CDNN)” framework is introduced to accurately predict the mechanical evolution of polymeric solids, by taking the example of injection-molded isotactic polypropylene. Upon built, the dual model is a parallel coupling of a “curve type classifier” and a “curve feature predictor” that predict, respectively, the stress–strain curve categories and their feature points that dictate the extent of similarity between two arbitrary curves in the same category, regardless of the curve complexity. Importantly, with the aid of curve-categorized knowledge, the CDNN strategy offers an update-to-date best balance in model accuracy (20% curve error in maximum) and simplicity (300 neurons in total), which greatly enhances the model’s extrapolability and interpretability and, in turn, mitigates the demanding data requirement (27 samplings from a 4D space, that is, a material design space consisting of 4 design dimensions to tune the structure). Overall, this work establishes a simple, robust methodology in predicting polymeric solids’ stress–strain curves and is potentially generic to a variety of materials.
Imparting polylactide (PLA) films with great heat resistance, transparency, and balanced mechanical performance simultaneous is a big challenge in academia and industry due to mutual exclusiveness of ...properties. In this work, a newfound strategy that combines elongational stress field and thermal field is proposed to reorganize the crystalline and amorphous structure of PLA films. It is discovered that the oriented PLA films with high draw ratios form a unique structure of the oriented amorphous phase restricted by the oriented nanosized crystal during thermal treatment at an appropriate temperature. Superb stiffness–toughness balance of the film is achieved as the elongation at break increases from 16 to 91.9% after the thermal treatment at 150 °C, while the yield strength increases from 50.0 to 76.0 MPa. It is worth noting that the PLA film also has excellent transparency, i.e., a transmittance as high as 86.6% (550 nm), owing to crystallites formed on the nanometer scale. Excellent heat resistance is also obtained, with the onset decline temperature increasing from 63.7 (for the unstructured casting film) to 77.1 °C due to increased crystallinity. Furthermore, a new understanding of the orientation of the amorphous phase promoted by the confinement effect to the toughening of PLA is obtained, and a phenomenal model for the thermal-treatment-induced toughening effect is proposed. This work could provide a significant guidance for the facile preparation of a PLA film with promising comprehensive properties of toughness–stiffness balance, high transparency, and good heat resistance.
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