144 research outputs found
Cyclomatrix polyphosphazenes frameworks (Cyclo-POPs) and the related nanomaterials : synthesis, assembly and functionalisation
Get PDFPoly (organophosphazene) (POP) is one of the most important inorganic polymers along with polysiloxane. The versatile phosphazene chemistry enables a wealth of functional inorganic-organic hybrid polymers with −P = N structures ranging from covalently crosslinked cyclomatrix phosphazene to linear POP copolymers. Cyclomatrix phosphazene framework materials (Cyclo-POPs) represent a novel type of molecular composites, and can be facilely formed via a rapid one-step polycondenzation and simultaneous self-assembly process under ambient conditions, and the stereoscopic morphologies are tuneable from zero-dimension (0D) to 3D depending on the compositions and reaction conditions. The novel cyclo-POPs have shown distinctive advantages over boron-containing covalent organic framework (COFs) materials in terms of the facile and rapid synthesis and integrated functionalities. Moreover, the highly crosslinked −P = N- backbone structures are readily to be transformed into porous carbon nanomaterials with intrinsically doped heteroatoms (P, N, S, O, B, depending on the framework skeletons), which are desirable for catalysis, sensors and energy storage applications. In this article, we critically overview the rational design, synthesis and functionalisation of the cyclo-POPs materials, and their emerging applications in optoelectronics, catalysis and energy storage devices, along with the technical challenges and development perspectives
Structure and dielectric properties of electroactive tetraaniline grafted non-polar elastomers
Get PDFIntrinsic modification of polybutadiene and block copolymer styrene–butadiene–styrene with the electrically conducting emeraldine salt of tetraaniline (TANI) via a three-step grafting method, is reported in this work. Whilst the TANI oligomer grafted at a similar rate to both polybutadiene and styrene–butadiene–styrene under the same conditions, the resulting elastomers exhibited vastly different properties. 1 mol% TANI-PB exhibited an increased relative permittivity of 5.9, and a high strain at break of 156%, whilst 25 mol% TANI-SBS demonstrated a relative permittivity of 6.2 and a strain at break of 186%. The difference in the behaviour of the two polymers was due to the compatibilisation of TANI by styrene in SBS through π-π stacking, which prevented the formation of a conducting TANI network in SBS at. Without the styrene group, TANI-PB formed a phase separated structure with high levels of TANI grafting. Overall, it was concluded that the polymer chain structure, the morphology of the modified elastomers, and the degree of grafting of TANI, had the greatest effect on the mechanical and dielectric properties of the resultant elastomers. This work paves the way for an alternative approach to the extrinsic incorporation of conducting groups into unsaturated elastomers, and demonstrates dielectric elastomers with enhanced electrical properties for use in actuation devices and energy harvesting applications
Fused deposition modelling (FDM) of composites of graphene nanoplatelets and polymers for high thermal conductivity : a mini-review
Get PDFComposites of polymers and the graphene family of 2D materials continue to attract great interest due their potential to dissipate heat, thus extending the in-service life of electronic and other devices. Such composites can be 3D printed using Fused Deposition Modelling into complex bespoke structures having enhanced properties, including thermal conductivity in different directions. While there are controversial opinions on the limitations of FDM for large-scale and high volume production (e.g. long production times, and expensive printers required), FDM is an innovative solution to the manufacture of small objects where effective thermal management is required and it is a valid alternative for the manufacture of (micro)-electronic components. There are few papers published on the FDM of functional composite materials based on graphene(s). In this mini-review, we describe the many technical challenges that remain to successful printing of these composites by FDM, including orientation effects, void formation, printing and feeding rates, nozzle and printing bed temperatures and the role each has in determining the thermal conductivity of any composite product made by FDM. We also compare these initial reports with those on FDM of other and related carbonaceous fillers, such as multi-walled carbon nanotubes and carbon fibre
Core-shell structured carbon nanoparticles derived from light pyrolysis of waste tires
Get PDFCarbon black nanoparticles (CBlp) were derived from waste tire rubbers via a melt-extrusion pyrolysis process at 300 °C. A polymeric shell was observed on the surface of CBlp, which was formed by bound rubber. The chemical structure and content of the bound rubber shell were characterized and quantified, and compared with the commercial carbon black N330 and pyrolytic carbon black (CBp). The average particle size of CBlp is about 22 nm, with a rubber shell thickness of 7–12 nm. Functional carboxylic group and ZnO were detected on the surface of CBlp by FTIR and XRD, respectively, which are absent from N330 and CBp. The core-shell structure of CBlp facilitate the dispersion and interfacial interaction in natural rubber, and lead to a higher reinforcement effect as compared those of N330 and CBp. The light pyrolysis process provides a facile and clean approach to generate useful carbon nanoparticles out of waste tire rubbers
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Effects of an ionic liquid and processing conditions on the ß-polymorph crystal formation in poly(vinylidene fluoride)
Get PDFThe piezoelectric properties of poly(vinylidene fluoride) (PVDF) are determined by the prevalence and orientation of its polar β-crystal phase, which can be tuned by processing conditions, additives, mechanical stretching or post-treatment. Here, the effects of three types of processing conditions on the crystalline structure evolution of PVDF were investigated; electrospinning, solution-casting and melt-compression. An ionic liquid (1-allyl-3-methylimidazolium chloride (AMIM)) used as an additive in aiding the electrospinning process, also affected the crystalline structure of the electrospun PVDF nanofibers. The total crystallinity, crystalline phase content and dielectric properties of the PVDF samples prepared by the different conditions were evaluated. The FTIR and DSC analyses show that the melt-compressed PVDF contains a high proportion of the paraelectric α-phase with a low total crystallinity, whereas the solution-cast PVDF contains a high proportion of polar γ-phase and a higher total crystallinity. In the case of the electrospun PVDF nanofibres, the addition of AMIM improved the morphology, uniformity and promoted the formation of the polar β and γ crystalline phases. X-Ray scattering analysis refined the crystal phase contents derived from FTIR, and also determined the ordered lamellar macromorphology formed by the three processing techniques. Furthermore, AMIM enhanced the a.c. conductivity and relative permittivity of the electrospun PVDF nanofibres by an order of magnitude, showing the effectiveness of using the ionic liquid AMIM, to improve the morphology and properties of electrospun PVDF nanofibers
Separation of core-shell structured carbon black nanoparticles from waste tires by light pyrolysis
Get PDFThe separation of core-shell structured carbon black (CBlp) nanoparticles from waste tires was investigated by applying a reactive extrusion process. The polymeric shell consisting primarily of crosslinked rubber and loosely bound rubber could be selectively separated by varying the extrusion temperature to 260, 280 and 300 °C. The structure, chemical composition and structure of the separated CBlp were characterized using thermo-gravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and dynamic light scattering. The crosslinked structure was persevered in the rubber shell of CBlp after extruding at 260 °C. A layer of loosely bound rubber was observed only in the rubber shell when extruded at 280 °C and 300 °C. The composition of the bound rubber layer is also dependent on the processing temperature
Heteroatom–doped hollow carbon microspheres based on amphiphilic supramolecular vesicles and highly crosslinked polyphosphazene for high performance supercapacitor electrode materials
Get PDFHybrid hollow polymeric microspheres (HPMSs) are synthesized by encapsulating the supramolecular vesicles with polyphosphazene through a rapid one-step polycondensation reaction. Subsequent carbonization treatments of the HPMSs lead to corresponding hollow carbon microspheres (HCMSs) with well-preserved geometry. The sizes of HPMSs and HCMSs are controlled by the vesicles, which is directly determined by the feeding ratio of the assembly units. Electrodes based on HCMSs showed a specific capacitance of 314.6 F/g at a current density of 0.2 A/g in 6 M KOH electrolyte, 180.0 F/g at a current density of 30 A/g, and high stability of 98.2% of capacity retention after 2000 cycles. Both the high surface area and high heteroatoms level of HCMSs contribute to the excellent capacitive performance. Meanwhile, the hollow carbon structure ensured the satisfactory capacitive performance by increasing utilization efficiency of the surface area as well as achieving short diffusion paths for electrolyte ions
Multiscale-structuring of polyvinylidene fluoride for energy harvesting:the impact of molecular-, micro- and macro-structure
Get PDFEnergy harvesting exploits ambient sources of energy such as mechanical loads, vibrations, human motion, waste heat, light or chemical sources and converts them into useful electrical energy. The applications for energy harvesting include low power electronics or wireless sensing at relatively lower power levels (nW to mW) with an aim to reduce a reliance on batteries or electrical power via cables and realise fully autonomous and self-powered systems. This review focuses on flexible energy harvesting system based on polyvinylidene fluoride based polymers, with an emphasis on manipulating and optimising the properties and performance of the polymeric materials and related nanocomposites through structuring the material at multiple scales. Ferroelectric properties are described and the potential of using the polarisation of the materials for vibration and thermal harvesting using piezo- and pyro-electric effects are explained. Approaches to tailor the ferroelectric, piezoelectric and pyroelectric properties of polymer materials are explored in detail; these include the influence of polymer processing conditions, heat treatment, nanoconfinement, blending, forming nanocomposites and electrospinning. Finally, examples of flexible harvesting devices that utilise the optimised ferroelectric polymer or nanocomposite systems are described and potential applications and future directions of research explored
Functionalization of BaTiO3 nanoparticles with electron insulating and conducting organophosphazene-based hybrid materials
Get PDFNovel core–shell structured organophosphazene (OPZ) coated BaTiO3 nanoparticles (OPZ@BaTiO3) were produced via a facile and rapid one-step nucleophilic substitution reaction in ambient conditions. The morphology, structure and textural properties of the core–shell nanoparticles were analysed via electron microscopy, spectroscopy, thermogravimetry and porosimetry, and the dielectric properties were evaluated by impedance spectroscopy. The thickness of the cross-linked OPZ shell was readily tailored by varying the weight ratio of the OPZ monomers to BaTiO3, which in turn affected the relative permittivity and the frequency dependence of the OPZ/BaTiO3 particles. A subsequent carbonisation treatment of the OPZ@BaTiO3 at 700 °C transformed the polymeric OPZ shell to a microporous carbonaceous shell, which dramatically increased the electrical conductivity of the particles. Organophosphazene chemistry offers a facile route to functionalise BaTiO3 nanoparticles without any pre-treatment, and generate a range of core–shell BaTiO3 nanoparticles with tailored dielectric and electrically conductive properties that can be used as active fillers for polymer based nanocomposites and energy storage applications. The effectiveness and advantages of OPZ chemistry over other reported methods in forming core–shell particles are demonstrated
2D boron nitride nanosheets (BNNS) prepared by high-pressure homogenisation : structure and morphology
Get PDF2D Boron Nitride Nano-sheets (BNNS) were prepared using a high-pressure homogenisation process to exfoliate bulk hexagonal boron nitride (h-BN). The effectiveness of this process was studied by characterising bulk h-BN and BNNS post-processing using numerous techniques. The BNNS produced was composed of a mixture of sheets having lengths on the nanometre (nm) scale, but lateral thicknesses on the micron (μm) length scale. The product was a macro-porous material containing slit-like pores with a surface area of 170 m2 g−1. It had a polycrystalline structure with d002 = 0.335 nm and L002 = 2 nm. From the sharp E2g peak in the Raman spectrum at 1360 cm−1 (FWHM = 12.5 cm−1), the sheets had a low defect density and were highly exfoliated. X-Ray photoelectron spectroscopy (XPS) studies detected B–OH and N–H groups on the BNNS surface and the presence of residual surfactant. Contact angle measurements (60° ± 3° (0 s); 40° ± 2° (10 s)) confirmed a hydrophilic surface. The BNNS was thermally stable under oxidative conditions up to 323 °C
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