White-Light-Emitting Polymer Composite Film Based on Carbon Dots and Lanthanide Complexes

A white-light-emitting polymer composite film was designed and synthesized by using carbon dots (CDs) and lanthanide complexes as primary light emitters and skillfully embedding them into a poly­(methyl methacrylate) (PMMA) matrix. The hydrophilic CDs used as blue light source were prepared and functionalized by copolymerizing with methacrylate to prevent their aggregate in the hydrophobic matrix. The lanthanide complexes Eu­(DBM)₃ and Tb­(DBM)₃ (DBM: dibenzoylmethide), in which the rare earth ions have not been fully coordinated, were fabricated and used as red and green emitters. The coordinatively unsaturated lanthanide ions could further coordinate with the oxygen atoms in the PMMA chains, which makes the complexes homogeneously dispersed in matrix as well as benefits to the energy transfer process. By adjusting the ratio of CDs, Eu­(DBM)₃ and Tb­(DBM)₃ in the matrix, the high transparent film with improved thermal stability, which prepared by a simple solution cast method, could emit pure white light (CIE coordinate located at (0.31, 0.32)) under 400 nm laser with a quantum efficiency of 16.6%. The energy transfer mechanism in the white-light-emitting material was also discussed

Self-Assembled Three-Dimensional Hierarchical Graphene/Polypyrrole Nanotube Hybrid Aerogel and Its Application for Supercapacitors

A three-dimensional hierarchical graphene/polypyrrole aerogel (GPA) has been fabricated using graphene oxide (GO) and already synthesized one-dimensional hollow polypyrrole nanotubes (PNTs) as the feedstock. The amphiphilic GO is helpful in effectively promoting the dispersion of well-defined PNTs to result in a stable, homogeneous GO/PNT complex solution, while the PNTs not only provide a large accessible surface area for fast transport of hydrate ions but also act as spacers to prevent the restacking of graphene sheets. By a simple one-step reduction self-assembly process, hierarchically structured, low-density, highly compressible GPAs are easily obtained, which favorably combine the advantages of graphene and PNTs. The supercapacitor electrodes based on such materials exhibit excellent electrochemical performance, including a high specific capacitance up to 253 F g^–1, good rate performance, and outstanding cycle stability. Moreover, this method may be feasible to prepare other graphene-based hybrid aerogels with structure-controllable nanostructures in large scale, thereby holding enormous potential in many application fields

Study on β‑Nucleated Controlled-Rheological Polypropylene Random Copolymer: Crystallization Behavior and a Possible Degradation Mechanism

Controlled-rheological polypropylene random copolymer (CRPPR) and β-nucleated CRPPR were prepared through peroxide-initiated reactive extrusion and their crystallization behaviors were comparatively investigated. Rheological experiments indicated that all degraded samples acquired better flow properties than undegraded samples and the addition of β-nucleating agent has little effect on the flowability. Unlike conventional controlled-rheological polypropylene homopolymer of which the shortened molecular chains are unfavorable for β-nucleation, the structure characterizations in this work demonstrated an unexpected increase in the β-phase content of degraded β-nucleated CRPPRs with elevated peroxide concentration. Successive self-nucleation and annealing thermal analysis revealed the generation of thicker lamellar in highly degraded samples, which implied that the stereo regularity improved when the molecular chain reacted with peroxide. Based on the experimental results, a possible degradation mechanism was proposed that free radicals preferentially attack the tertiary carbon atoms adjacent to ethylene co-units during the degradation reaction, which resulted in a reduction of stereo errors, and, consequently, improvement of the β-crystallization ability

Highly Thermally Conductive Composite Films Based on Nanofibrillated Cellulose in Situ Coated with a Small Amount of Silver Nanoparticles

In this paper, a freestanding flexible nanofibrillated cellulose (NFC)/silver (Ag) composite film with high thermal conductivity (TC) was prepared using the NFC that was in situ coated with a small amount of Ag nanoparticles through mussel-inspired chemistry of dopamine. The results demonstrated that Ag nanoparticles were homogeneously coated on the surface of NFC nanofibers and their incorporation had little influence on the film-forming ability of NFC. The NFC decorated with Ag nanoparticles could easily form thermally conductive pathways in the composite films, and the resultant films containing only 2.0 vol % of Ag showed a high in-plane TC value of 6.0 W/(m·K), which was 4 times that of pure NFC film. Moreover, the composite films exhibited relatively high strength and flexibility. The highly thermally conductive NFC/Ag composite films possess potential applications as lateral heat spreaders in flexible electronic equipment

Highly in-Plane Thermally Conductive Composite Films from Hexagonal Boron Nitride Microplatelets Assembled with Graphene Oxide

With the development of portable and flexible devices, demands for high-performance thermal management materials with high in-plane thermal conductivity (TC), mechanical flexibility, and electrical insulation are growing. Hexagonal boron nitride (BN) is a promising thermally conductive filler due to its high in-plane TC and electrical insulation. In this work, taking full advantage of good film-forming feature of graphene oxide (GO) suspension and its ability to stably disperse BN microplatelets (BNMPs) in the aqueous medium, the GO/BNMPs composite films with high in-plane TCs were prepared by a simple cast-drying method. The structure characterization demonstrated that GO can induce BNMPs to preferably arrange in-plane orientation in the composite films. The resultant composite films possessed a maximum in-plane TC value of 10.3 W/m·K at 50 wt % BNMPs. Moreover, the films exhibited excellent mechanical flexibility and satisfactory electrical insulation. The proposed method of fabricating BNMPs-based composite films in this work is facile handling, eco-friendly, and suitable for large-scale production, and it therefore enables potential applications in flexible electronics

Polydopamine As an Efficient and Robust Platform to Functionalize Carbon Fiber for High-Performance Polymer Composites

Carbon fibers (CFs), which exhibit excellent physical performances and low density, suffer from their low surface activity in some application. Herein, based on dopamine chemistry, we proposed an efficient method to functionalize them: through a simple dip-coating procedure, the CFs were inverted from amphiphobic to hydrophilic with deposition of polydopamine film. Furthermore, using polydopamine as a bridge, the hydrophilic functionalized CFs were transformed to be oleophilic after following octadecylamine grafting. To illustrate applications of this functionalization strategy, we added 15 wt % functionalized CFs into polar epoxy and nonpolar poly­(ethylene-co-octene), and as a consequence, their tensile strength respectively increase by 70 and 60%, which show greater reinforcing effect than the unmodified ones (35 and 35%). The results of dynamic mechanical analysis and scanning electron microscope observations indicate that this polydopamine-based functionalization route brought about satisfactory improvements in interfacial adhesion between fillers and matrix. Considering that this simple approach is facile and robust enough to allow further specific functionalization to adjust surface properties, these findings may lead to the development of new efficient strategies for surface functionalization of CFs that are of great interest to the industrial field

Deposition of Three-Dimensional Graphene Aerogel on Nickel Foam as a Binder-Free Supercapacitor Electrode

We reported a new type of graphene aerogel–nickel foam (GA@NF) hybrid material prepared through a facile two-step approach and explored its energy storage application as a binder-free supercapacitor electrode. By simple freeze-drying and the subsequent thermal annealing of graphene oxide hydrogel–NF hybrid precursor, three-dimensional graphene aerogels with high mass, hierarchical porosity, and high conductivity were deposited on a NF framework. The resulting binder-free GA@NF electrode exhibited satisfactory double-layer capacitive behavior with high rate capability, good electrochemical cyclic stability, and a high specific capacitance of 366 F g^–1 at a current density of 2 A g^–1. The versatility of this approach was further verified by the successful preparation of 3D graphene/carbon nanotube hybrid aerogel–NF as a supercapacitor electrode, also with improved electrochemical performance. With advantageous features, such a facile and versatile fabrication technique shows great promise in the preparation of various types of carbon–metal hybrid electrodes

Low-Density, Mechanical Compressible, Water-Induced Self-Recoverable Graphene Aerogels for Water Treatment

Graphene aerogels (GAs) have demonstrated great promise in water treatment, acting as separation and sorbent materials, because of their high porosity, large surface area, and high hydrophobicity. In this work, we have fabricated a new series of compressible, lightweight (3.3 mg cm^–3) GAs through simple cross-linking of graphene oxide (GO) and poly­(vinyl alcohol) (PVA) with glutaraldehyde. It is found that the cross-linked GAs (xGAs) show an interesting water-induced self-recovery ability, which can recover to their original volume even under extremely high compression strain or after vacuum-/air drying. Importantly, the amphiphilicity of xGAs can be adjusted facilely by changing the feeding ratio of GO and PVA and it exhibits affinity from polar water to nonpolar organic liquids depended on its amphiphilicity. The hydrophobic xGAs with low feeding ratio of PVA and GO can be used as adsorbent for organic liquid, while the hydrophilic xGAs with high feeding ratio of PVA and GO can be used as the filter material to remove some water-soluble dye in the wastewater. Because of the convenience of our approach in adjusting the amphiphilicity by simply changing the PVA/GO ratio and excellent properties of the resulting xGAs, such as low density, compressive, and water-induced self-recovery, this work suggests a promising technique to prepare GAs-based materials for the water treatment in different environment with high recyclability and long life

Regulation of Physical Networks and Mechanical Properties of Triblock Thermoplastic Elastomer through Introduction of Midblock Similar Crystalline Polymer with Multiblock Architecture

The physical network structure and mechanical properties of styrene-<i>b</i>-(ethylene-<i>co</i>-butylene)-<i>b</i>-styrene (SEBS) were regulated through rational introduction of crystalline olefin multiblock copolymer (OBC). This copolymer comprised alternated crystallizable and amorphous blocks, both of which had similar composition with ethylene-<i>co</i>-butylene (EB) blocks of SEBS. Polarized optical microscope and atom force microscope observations revealed that OBC exhibited distinct crystalline morphologies in blends. On one hand, major OBC chains were macrophase separated with SEBS, generating bulk crystals. On the other hand, small OBC particle crystals with diameter around 10 nm could be distinguished in the SEBS matrix as well. Considering the unique multiblock architecture of OBC, particle crystals could be regarded as additional physical netpoints to SEBS networks as the corresponding amorphous blocks entangled with continuous EB blocks. Because of the interesting crystalline behaviors of OBC in the SEBS matrix, the blend exhibited dramatically elevated elongation at break at both room temperature and relatively high temperature without sacrifice of intrinsic elasticity. We believe this work sheds light on comprehending the interaction between triblock elastomers and blended polymers, and it also demonstrates the feasibility of regulating the apparent properties of triblock copolymers by the blending approach

Exploring the Application of Sustainable Poly(propylene carbonate) Copolymer in Toughening Epoxy Thermosets

Herein, poly­(propylene carbonate) (PPC) was used as initiator for ε-caprolactone polymerization to produce the poly­(ε-caprolactone)-<i>block</i>-poly­(propylene carbonate)-<i>block</i>-poly­(ε-caprolactone) (PCL-PPC-PCL) triblock copolymer, enabling innovative application of PPC as a toughening agent of epoxy thermosets. The interfacial interaction between PPC modifiers and epoxy was enhanced significantly because PCL blocks were miscible with epoxy matrix. The size of separated PPC modifiers decreased dramatically as the amphiphilic block copolymer formed nanophases in epoxy host. Consequently, with the incorporation of 30 wt % PCL-PPC-PCL modifier into the thermoset, the tensile elongation and the area under the stress–strain curves increased by more than 320% and 180%, respectively, compared with neat epoxy, indicating that an excellent toughening effect was achieved using this strategy. Considering that PPC possessed an ocean of attractive properties but suffered from its low glass transition temperature in implementation as mass products, this work may open up opportunities to extend the applications of PPC