36 results found
Wang J, Anthony DB, Fuentes CA, et al., 2022, Wettability of carbon nanotube-grafted carbon fibers and their interfacial properties in polypropylene thermoplastic composite, Composites Part A: Applied Science and Manufacturing, Vol: 159, Pages: 1-10, ISSN: 1359-835X
The interfacial properties of carbon fiber (CF) reinforced thermoplastic composites depend strongly on the wettability and surface characteristics of the reinforcing fibers, and their compatibility with a chosen matrix. The interface between conventional fibers and thermoplastic matrices is generally weak, due to a lack of specific chemical interaction, especially in the case of polyolefins. Carbon nanotube-grafted-carbon fibers (CNT-g-CF) are considered to be potential reinforcements as they provide additional mechanical interlocking. Commercial CFs were successfully grafted with nanotubes using a continuous, and hence scalable, CVD method. X-ray photoelectron spectroscopy, Wilhelmy wetting measurements, and scanning electron microscopy confirmed the successful grafting and resulting hydrophobic surface chemistry, dominated by van der Waals interactions. The grafted CNTs, with diameters and lengths around 10 nm and 140 nm respectively, were well suited to improve the overall wettability and interfacial shear strength (+53.4 %) of the CNT-g-CF in a polypropylene matrix when compared to as-received unsized CFs.
Valkova M, Anthony DB, Kucernak ARJ, et al., 2022, Predicting the mechanical behaviour of structural supercapacitor composites, Composites Part A: Applied Science and Manufacturing, Vol: 156, ISSN: 1359-835X
Multifunctional structural power composites may transform transport electrification, and other applications, but require performance and reliability improvements. Computational modelling has the potential to accelerate their development and deployment. This work addresses the lack of predictive models for the mechanical behaviour of structural supercapacitor composites exploiting carbon aerogel-modified carbon fabric electrodes. The elastic behaviour was investigated using finite element analysis of quasi-meso-scale periodic unit cell models, considering the effects of constituent properties, defects, stacking geometry, and boundary conditions. Nanoindentation was used to evaluate the Young’s modulus of carbon aerogel. Parametric modelling demonstrated a strong influence of the ply offset and matrix materials on the composite elastic properties. The initial numerical results overpredicted the actual performance measured from tensile and in-plane shear experiments in the literature. Optical, scanning electron and micro X-ray imaging revealed extensive pre-cracking and voidage in the physical laminates. Additional computational investigations showed that the pre-cracks were associated with a degradation of shear stiffness. The remaining performance gap was attributed to voidage. The present study highlights that challenges for mechanical performance and its prediction stem from the presence of processing defects and a lack of in-situ material data. Nevertheless, the models identify the potential of hierarchical laminates containing aerogels to generate sizable performance improvements, both in multifunctional and purely structural contexts.
Pernice MF, Qi G, Senokos E, et al., 2022, Mechanical, electrochemical and multifunctional performance of a CFRP/carbon aerogel structural supercapacitor and its corresponding monofunctional equivalents, Multifunctional Material, Vol: 5
Qi G, Nguyen S, Anthony DB, et al., 2021, The influence of fabrication parameters on the electrochemical performance of multifunctional structural supercapacitors, Multifunctional Materials, Vol: 4, ISSN: 2399-7532
Multifunctional structural supercapacitors based on carbon fibre electrodes (CF) and structural electrolytes (SEs) can realise multifunctionality by simultaneously bearing load and providing electrochemical energy storage. Structural supercapacitor constituents (i.e. electrodes and electrolytes) have undergone significant development to enhance their electrochemical and mechanical properties. However, the fabrication of fully functional devices presents a number of practical challenges to achieve optimal multifunctional properties, particularly those associated with assembly and lamination. This work investigated the effect of separator selection and processing parameters on the electrochemical performance of structural supercapacitors, as well as evaluating the repeatability of the SE filming process. Two layers of glass fibre fabrics were the most effective separator for preventing short-circuiting of the structural supercapacitors. The weight fraction of the SE matrix had a significant effect on the capacitance, energy and power of the structural supercapacitors. By addressing such fabrication challenges, high performance structural supercapacitors can be manufactured with greater reproducibility and at larger scales such that they are suitable for integration in industrial applications.
De Luca H, Anthony D, Greenhalgh E, et al., 2020, Piezoresistive structural composites reinforced by carbon nanotube-grafted quartz fibres, Composites Science and Technology, Vol: 198, Pages: 1-12, ISSN: 0266-3538
Nano-engineered fibre/matrix interfaces can improve state-of-the-art fibre-reinforced composites. Grafting carbon nanotubes (CNTs) to high temperature quartz glass fibres produces “hairy” or “fuzzy” fibres, which combine reinforcements at micrometre and nanometre length scales. Fuzzy quartz fibres were produced continuously, reel-to-reel, on whole tows, in an open chemical vapour deposition reactor. The resulting uniform coverage of 200 nm long CNTs increased the interfacial shear strength with epoxy (90.3 ± 2.1 MPa) by 12% compared to the commercially-sized counterpart, as measured by single fibre pull-out tests. The improved interfacial properties were confirmed at the macroscale using unidirectional hierarchical bundle composites, which exhibited a delayed onset of fibre/matrix debonding. Although the quartz fibres are electrically insulating, the grafted CNT create a conductive path, predominantly parallel to the fibres. To explore the applicability for structural health monitoring, the resistivity was recorded in situ during mechanical testing, and correlated with simultaneous acoustic emission data. The baseline resistivity parallel to the fibres (ρ0 = 3.9 ± 0.4 × 10−1 Ω m) displayed a linear piezoresistive response (K = 3.64) until failure at ca. 2.1% strain, also referred to as "gauge factor”, a two-fold improvement over traditional resistance strain gauges (e.g. constantan). Hierarchical, fuzzy quartz fibres, therefore, simultaneously enhance both structural and sensing performance, offering multifunctional opportunities in large composite parts.
Senokos E, Anthony D, Nguyen S, et al., 2020, Manganese dioxide decorated carbon aerogel/carbon fibre composite as a promising electrode for structural supercapacitors, 22nd International Conference on Composite Materials 2019 (ICCM22), Publisher: Engineers Australia, Pages: 1-8
Manganese dioxide electrochemically deposited onto carbon aerogel/carbon fibres (CAG/CF) shows a great potential as an electrode material in multifunctional structural supercapacitors. MnO₂ nanowires grown by a pulse potentiometric method provide a large enhancement in capacitive performance of the carbon electrodes and symmetric supercapacitor devices based on the hybrid material.
Valkova M, Anthony DB, Kucernak ARJ, et al., 2020, Predicting the compaction of hybrid multilayer woven composite reinforcement stacks, Composites Part A: Applied Science and Manufacturing, Vol: 133, ISSN: 1359-835X
A meso-scale finite element modelling strategy was developed to investigate the effect of hybridisation on the compaction response of multilayer stacks combining glass and carbon dry woven fabrics. It is expected that the electrochemical-mechanical properties of emerging multifunctional hybrid composites are strongly dictated by the morphology of the compacted reinforcements, yet no investigations into their compressibility have been reported. Model predictions were evaluated against compressibility measurements for monolithic and hybrid fabric stacks. The ply offset had a major influence on the predicted internal morphologies and fibre content, contributing to experimental variability thereof. Optical microscopy and micro X-ray computed tomography imaging indicated greater likelihood of intermediate ply offsets in physical specimens, over limit case model idealisations. Compressibility was slightly reduced in the hybrid multilayer stacks studied in this work. The model outputs presented are being used to analyse the electrochemical-mechanical response of hybrid woven structural power composites.
Lee WJ, Paineau E, Anthony DB, et al., 2020, Inorganic nanotube mesophases enable strong self-healing fibers, ACS Nano, Vol: 14, Pages: 5570-5580, ISSN: 1936-0851
The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. Double walled aluminogermanate imogolite nanotubes are geo-inspired analogs of carbon nanotubes, synthesized at low temperature, with complementary properties. Here, continuous imogolite based fibers are wet spun within a polyvinyl alcohol matrix. The lyotropic liquid crystallinity of the system produces highly aligned fibers with tensile stiffness and strength up to 24.1 GPa (14.1 N tex⁻¹) and 0.8 GPa (0.46 N tex⁻¹), respectively. Significant enhancements over the pure polymer control are quantitatively attributed to both matrix refinement and direct nanoscale reinforcement, by fitting an analytical model. Most intriguingly, imogolite-based fibers show a high degree of healability via evaporation induced self assembly, recovering up to 44%, and 19% of the original fiber tensile stiffness and strength, respectively. This recovery at high absolute strength highlights a general strategy for the development of high-performance healable fibers relevant to composite structures and other applications.
Clancy AJ, Anthony DB, De Luca F, 2020, Metal mimics: lightweight, strong, and tough (nano)composites and nanomaterial assemblies, ACS Applied Materials & Interfaces, Vol: 12, Pages: 15955-15975, ISSN: 1944-8244
The ideal structural material would be high strength and stiffness, with a tough ductile failure, all with a low density. Historically, no such material exists, and materials engineers have had to sacrifice a desired property during materials selection, with metals (high density), fibre composites (brittle failure), and polymers (low stiffness) having fundamental limitations on at least one front. The ongoing revolution of nanomaterials provides a potential route to build on the potential of fibre-reinforced composites, matching their strength while integrating toughening behaviours akin to metal deformations all while using low weight constituents. Here, the challenges, approaches, and recent developments of nanomaterials for structural applications are discussed, with an emphasis on improving toughening mechanisms – often the neglected factor in a field which chases strength and stiffness.
Nguyen S, Anthony DB, Qian H, et al., 2019, Mechanical and physical performance of carbon aerogel reinforced carbon fibre hierarchical composites, Composites Science and Technology, Vol: 182, ISSN: 0266-3538
Carbon aerogel (CAG) is a potential hierarchical reinforcement to improve the matrix-dominated mechanical properties of continuous carbon fibre reinforced polymer (CFRP) composites in both multifunctional and purely structural applications. When using CAG to reinforce a polyethylene glycol diglycidyl ether (PEGDGE) matrix, the interlaminar shear strength, compressive modulus and strength increased approximately four-fold, whilst the out-of-plane electrical conductivity increased by 118%. These mechanical and electrical performance enhancements significantly improve the multifunctional efficiency of composite structural supercapacitors, which can offer weight savings in transport and other applications. However, CAG also has the potential to reinforce conventional continuous CF composites in purely structural contexts. Here, CAG reinforcement of structural epoxy resin composites marginally increased compressive (1.4%) and tensile (2.7%) moduli respectively, but considerably reduced compressive, tensile and interlaminar shear strengths. Fractographic analysis shows that the reduced performance can be attributed to poor interfacial adhesion; in the future, alternative processing routes may resolve these issues to achieve advances in both moduli and strengths over conventional structural CFRPs.
Anthony D, Nguyen S, Senokos E, et al., 2019, Hierarchical carbon aerogel modified carbon fiber composites for structural power applications, 22nd International Conference on Composite Materials 2019 (ICCM22), Publisher: Engineers Australia, Pages: 1-7
The desire to reduce overall weight in devices is a key driver for perpetual material development; the ability to combine composites with energy storage functions/capabilities which simultaneously provide structural integrity has the potential to supersede monofunctional components. To achieve this ambition, the multifunctional structure must perform both mechanical and energy storage functions sufficiently, but often there is a trade off in performance which is a significant challenge to overcome. Carbon aerogels have been shown to contribute positively to (electro-chemical double layer) capacitive performance due to an increased surface area in multifunctional carbon fiber based composite electrodes, but have also been shown to reduce mechanical properties; the addition of nanoscale reinforcers, such as carbon nanotubes, graphene or alike, with their superlative electrical and mechanical properties are proposed to address these concerns and create a truly hierarchical structure suitable for structural power applications.
Lee WJ, Clancy AJ, Fernandez-Toribio JC, et al., 2019, Interfacially-grafted single-walled carbon nanotube / poly (vinyl alcohol) composite fibers, CARBON, Vol: 146, Pages: 162-171, ISSN: 0008-6223
Clancy A, Sirisinudomkit P, Anthony D, et al., 2019, Real-time mechanistic study of carbon nanotube anion functionalisation through open circuit voltammetry, Chemical Science, Vol: 10, Pages: 3300-3306, ISSN: 2041-6520
The mechanism of the functionalisation of reduced single walled carbon nanotubes with organobromides was monitored byopen circuit voltammetry throughout the reaction and further elucidated through a series of comparative reactions. Thedegree of functionalisation was mapped against the reagent reduction potential, degree of electron donation of substituents(Hammett parameter), and energies calculated, ab initio, for dissociation and heterolytic cleavage of the C-Br bond. Incontrast to the previously assumed reduction/homolytic cleavage mechanism, the reaction was shown to consist of a rapidassociation of carbon-halide bond to the reduced nanotube as a complex, displacing surface-condensed countercations,leading to an initial increase in the net nanotube surface negative charge. The complex subsequently slowly degradesthrough charge transfer from the reduced single-walled carbon nanotube to the organobromide, utilizing charge, and thecarbon-halide bond breaks heterolytically. Electron density on the C-Br bond in the initial reagent is the best predictor fordegree of functionalisation, with more electron donating substituents increasing the degree of functionalisation. Both themechanism and the new application of OCV to study such reactions are potentially relevant to wide range of related systems.
Clancy A, Anthony DB, Shaffer M, 2019, Reactive coagulation of single-walled carbon nanotubes for tougher composites – solution processing and assembly, Polymer Processing Society Europe Africa Conference 2017 (PPS 2017) with 7th International Conference on Carbon NanoParticle Based Composites (CNPComp2017), Publisher: AIP Publishing, Pages: 090005-090005, ISSN: 1551-7616
The injection of reduced single-walled carbon nanotubes into a coagulation bath of polyvinyl chloride (PVC) solution leads to the formation of nanocomposite fibres with polymer covalently bound to the nanotubes. The influence of PVC concentration and molecular weight, and the extrusion diameter on the nanocomposite fibre tensile properties and composition have been examined. The nanocomposite fibres produced have strengths as high as 480 MPa and modulus of 15 GPa, making them the strongest and stiffest PVC composites recorded to date.
Liu B, Liu C, De Luca H, et al., 2019, Synthesis of epoxidized poly(ester carbonate)-b-polyimide-b-poly(ester carbonate): reactive single-walled carbon nanotube dispersants enable synergistic reinforcement around multi-walled nanotube-grafted carbon fibers, Polymer Chemistry, Vol: 10, Pages: 1324-1334, ISSN: 1759-9954
Polyimides (PI) generally have a high affinity for single-walled carbon nanotubes (SWNTs), but they suffer from poor solubility in most low boiling point organic solvents and low compatibility with common resins (such as epoxy) used in composites, limiting their suitability as dispersants. PI block copolymer systems containing reactive poly(ester carbonate)s have not yet been reported and are expected to act as effective reactive dispersing agents of SWNTs. Herein, PI-derived block copolymers are synthesized via ring-opening copolymerization of lactide (LA) (a control monomer) and allyl-bearing 2-methyl-2-(allyloxycarbonyl)-propylene carbonate (MAC) from the OH-terminal ends of the PI block to produce PLA-PI-PLA (TB1, a control) and PMAC-PI-PMAC (TB2). The allyl pendant group of TB2 allows further facile functionalization to form a third series of epoxidized (EP) derivatives, i.e. PMACEP-block-PI-block-PMACEP (TB3). TB3 copolymer when mixed with a conventional structural epoxy resin forms blends that do not show inferior tensile properties compared with the epoxy, which is unusual. Furthermore, the mixing solvent tetrahydrofuran (THF) can be readily evaporated off after forming the blends. TB3-dispersed (2 wt%) SWNTs added to epoxy increased the tensile strength, modulus, and elongation at break of the resulting nanocomposite films by 40%, 34%, and 26% respectively, compared to the baseline epoxy resin. Furthermore, when TB3b triblock-dispersed SWNTs in epoxy were combined with fuzzy carbon fibers, i.e. carbon nanotube-grafted-carbon fibers (CNT-g-CF), a synergistic interfacial strength reinforcement was observed, together with shifting of the failure mode from the matrix interphase to the carbon fiber-grafted nanotube interface. The ultimate interfacial shear strength between the TB3-dispersed SWNT-epoxy matrix and the fuzzy carbon fibers (i.e., fibers having carbon nanotubes grown on them) measured via single fiber pull-out tests was 100 MPa, which was ca. 11% imp
Anthony DB, Sui X, Kellersztein I, et al., 2018, Continuous carbon nanotube synthesis on charged carbon fibers, Composites Part A: Applied Science and Manufacturing, Vol: 112, Pages: 525-538, ISSN: 1359-835X
Carbon nanotube grafted carbon fibers (CNT-g-CFs) were prepared continuously, spool to spool, via thermal CVD. The application of an in-situ potential difference (300 V), between the fibers and a cylindrical graphite foil counter electrode, enhanced the growth, producing a uniform coverage of carbon nanotubes with diameter ca. 10 nm and length ca. 125 nm. Single fiber tensile tests show that this approach avoids the significant reduction of the underlying carbon fiber strengths, which is usually associated with CVD grafting processes. Single fiber fragmentation tests in epoxy, with in-situ video fragment detection, demonstrated that the CNT-g-CFs have the highest interfacial shear strength reported for such systems (101 ± 5 MPa), comparable to state–of–the–art sizing controls (103 ± 8 MPa). Single fiber pull-out data show similar trends. The short length of the grafted CNTs is particularly attractive for retaining the volume fraction of the primary fibers in composite applications. The results are compared with a short review of the interfacial data available for related systems.
Anthony DB, Bacarreza Nogales O, Shaffer M, et al., 2018, Pseudo-ductile failure mechanism introduced into finger jointed thermoplastic PES interleaved CFRC, ECCM18 - 18th European Conference on Composite Materials
Pre-cut unidirectional carbon fibre prepreg composites, with an overlapped finger-joint architecture, were modified through the addition of polyethersulfone (PES) interleaves. The properties arising from these finger-jointed configurations were strongly dependent on the interply overlap region. When the tough thermoplastic interleaves spanned only the central portion of the overlap, a crack arresting failure mechanism was observed in tension. A pronounced plateau region or pseudo-ductile response was shown in conjunction with a strain hardening response after crack arrest. The local strain-to-failure of PES interleaved samples was ~3.2%, an increase of 85% compared to the pre-cut baseline (strain-to-failure 1.6%, pre-cut specimens without interleaves).
De Luca F, Clancy A, Rubio Carrero N, et al., 2018, Increasing carbon fiber composite strength with a nanostructured“brick-and-mortar” interphase, Materials Horizons, Vol: 5, Pages: 668-674, ISSN: 2051-6355
Conventional fiber-reinforced composites suffer from the formation of critical clusters of correlated fiber breaks, leading to sudden composite failure in tension. To mitigate this problem, an optimized “brick-and-mortar” nanostructured interphase was developed, in order to absorb energy at fiber breaks and alleviate local stress concentrations whilst maintaining effective load transfer. The coating was designed to exploit crack bifurcation and platelet interlocking mechanisms known in natural nacre. However, the architecture was scaled down by an order of magnitude to allow a highly ordered conformal coating to be deposited around conventional structural carbon fibers, whilst retaining the characteristic phase proportions and aspect ratios of the natural system. Drawing on this bioinspiration, a Layer-by-Layer assembly method was used to coat multiple fibers simultaneously, providing an efficient and potentially scalable route for production. Single fiber pull out and fragmentation tests showed improved interfacial characteristics for energy absorption and plasticity. Impregnated fiber tow model composites demonstrated increases in absolute tensile strength (+15%) and strain-to-failure (+30%), as compared to composites containing conventionally sized fibers.
Woodward RT, Markoulidis F, De Luca F, et al., 2018, Carbon foams from emulsion-templated reduced graphene oxide polymer composites: electrodes for supercapacitor devices, Journal of Materials Chemistry A, Vol: 6, Pages: 1840-1849, ISSN: 2050-7496
Amphiphilic reduced graphene oxide (rGO) is an efficient emulsifier for water-in-divinylbenzene (DVB) high internal phase emulsions. The polymerisation of the continuous DVB phase of the emulsion template and removal of water results in macroporous poly(divinylbenzene) (polyDVB). Subsequent pyrolysis of the poly(DVB) macroporous polymers yields ‘all-carbon’ foams containing micropores alongside emulsion templated-macropores, resulting in hierarchical porosity. The synthesis of carbon foams, or ‘carboHIPEs’, from poly(DVB) produced by polymerisation of rGO stabilised HIPEs provides both exceptionally high surface areas (up to 1820 m2/g) and excellent electrical conductivities (up to 285 S/m), competing with the highest figures reported for carboHIPEs. The use of a 2D carbon emulsifier results in the elimination of post-carbonisation treatments to remove standard inorganic particulate emulsifiers, such as silica particles. It is demonstrated that rGO containing carboHIPEs are good candidates for supercapacitor electrodes where carboHIPEs derived from more conventional polymerised silica-stabilised HIPEs perform poorly. Supercapacitor devices featured a room-temperature ionic liquid electrolyte and electrodes derived from either rGO- or silica-containing poly(DVB)HIPEs and demonstrated a maximum specific capacitance of 26 F g-1, an energy density of 5.2 Wh kg-1 and a power density of 280 W kg-1.
Buckley DJ, Hodge SA, De Marco M, et al., 2017, Trajectory of the Selective Dissolution of Charged Single-Walled Carbon Nanotubes, Journal of Physical Chemistry C, Vol: 121, Pages: 21703-21712, ISSN: 1932-7447
Single-Walled Carbon Nanotubes (SWCNTs) are materials with an array of remarkable physical properties determined by their geometries, however, SWCNTs are typically produced as a mixture of different lengths and electronic types. Consequently, many methods have been developed to sort the as-produced SWCNT samples by their physical cha-racteristics, often requiring aggressive and unscalable techniques to overcome the strong bundling forces between the nanotubes. Previously, it has been shown that negatively charging SWCNTs can lead to their thermodynamically-driven dissolution in polar solvents, and moreover that this process can selectively dissolve different SWNCT species, albeit with contrasting claims of selectivity. Here we carefully investigate dissolution as a function of charge added to the SWCNT starting material, using a range of complementary techniques. We uncover a far richer dependence on charge of SWCNT dissolution than previously reported. At low charge added, amorphous carbons preferentially dissolve, followed sequentially by metallic, larger diameter semiconducting SWCNTs, and finally smaller diameter semiconducting SWCNTs. At an optimal value, the dissolution yield is maximized across all species, however at higher charge than this we find the larger diameter and metallic SWCNTs are so charged they are no longer soluble, leaving smaller diameter SWCNTs in solution. Our results therefore clearly demonstrate two interconnected mechanisms for dissolution: on one hand charging of the SWNCTs based on their respective electron affinities on the other the solution thermodynamics. This work reconciles contrasting reports in the literature, provides a blueprint for scalable SWCNT separation and more generally demonstrates the..
Anthony DB, Bacarreza Nogales OR, Shaffer MSP, et al., 2017, Crack arrest in finger jointed thermoplastic interleaved CFRC, 21st International Conference on Composite Materials, Publisher: Chinese Society for Composite Materials
Pre-cut unidirectional carbon fibre prepreg (M21/194/34%/T800S) composites were tested in tension with a 20 mm overlapped finger joint architectures. In between the overlapping finger jointed region the effect of introducing polyethersulfone (PES) interleaves is investigated. Samples with the addition of a thick PES interleave arrested the initial crack which formed at the pre-cut site. The strain-to-failure of the thick PES interleaved samples was over 3.2%, an increase of 85% compared to the baseline samples, and catastrophic failure was delayed in the majority of instances.
De Luca, Anthony DB, Greenhalgh ES, et al., 2017, Continuous production of carbon nanotube-grafted quartz fibres: Effect of carbon nanotube length on fibre/matrix adhesion, 21st International Conference on Composite Materials, Publisher: Chinese Society for Composite Materials
Here, the continuous production of carbon nanotube-grafted-quartz-fibres was performed in an open chemical vapour deposition reactor with continuous in line catalyst deposition. Highly graphitic carbon nanotubes (CNTs) with controllable lengths ranging from 0.1 μm to 20 μm were grown on the quartz fibre surface by adjusting the reduction and growth times, with shorter fibres growing homogeneously and longer CNTs growing in a splayed “Mohawk” manner. The effect of CNTs length (and thus microstructure) upon the mechanical properties of CNT-grafted-quartz-fibre/epoxy composites was investigated through single fibre pull-out test. The presence of a uniform coverage of sub-micron long CNTs led to an increase in interfacial shear strength of 11% and 29% when compared to sized and de-sized quartz fibres, respectively.
Anthony DB, Qian H, Clancy AJ, et al., 2017, Applying a potential difference to minimise damage to carbon fibres during carbon nanotube grafting by chemical vapour deposition, Nanotechnology, Vol: 28, ISSN: 1361-6528
The application of an in-situ potential difference between carbon fibres and a graphite foil counter electrode (300 V, generating an electric field ca. 0.3 V μm-1 to 0.7 V μm-1) during the chemical vapour deposition synthesis of carbon nanotube (CNT) grafted carbon fibres, significantly improves the uniformity of growth without reducing the tensile properties of the underlying carbon fibres. Grafted carbon nanotubes with diameters around 55 nm and lengths around 10 μm were well attached to the carbon fibre surface, and were grown without the requirement for protective barrier coatings. The grafted CNTs increased the surface area to 185 m2 g-1 compared to the as-received sized carbon fibre 0.24 m2 g-1. The approach is not restricted to batch systems and has the potential to improve carbon nanotube grafted carbon fibre production for continuous processing.
Clancy AJ, anthony D, Fisher S, et al., 2017, Reductive dissolution of supergrowth carbon nanotubes for tougher nanocomposites by reactive coagulation spinning, Nanoscale, Vol: 9, Pages: 8764-8773, ISSN: 2040-3372
Long single-walled carbon nanotubes, with lengths >10 μm, can be spontaneously dissolved by stirring in a sodium naphthalide N,N-dimethylacetamide solution, yielding solutions of individualised nanotubide ions at concentrations up to 0.74 mg mL−1. This process was directly compared to ultrasonication and found to be less damaging while maintaining greater intrinsic length, with increased individualisation, yield, and concentration. Nanotubide solutions were spun into fibres using a new reactive coagulation process, which covalently grafts a poly(vinyl chloride) matrix to the nanotubes directly at the point of fibre formation. The grafting process insulated the nanotubes electrically, significantly enhancing the dielectric constant to 340% of the bulk polymer. For comparison, samples were prepared using both Supergrowth nanotubes and conventional shorter commercial single-walled carbon nanotubes. The resulting nanocomposites showed similar, high loadings (ca. 20 wt%), but the fibres formed with Supergrowth nanotubes showed significantly greater failure strain (up to ∼25%), and hence more than double the toughness (30.8 MJ m−3), compared to composites containing typical ∼1 μm SWCNTs.
Woodward RT, Jobbe-Duval A, Marchesini S, et al., 2017, Hypercrosslinked polyHIPEs as precursors to designable, hierarchically porous carbon foams, Polymer, Vol: 115, Pages: 146-153, ISSN: 0032-3861
Hierarchically porous carbon foams were produced by carbonization of hypercrosslinked polymerized high internal phase water-in-styrene/divinylbenzene emulsions (HIPEs). The hypercrosslinking of these poly(ST-co-DVB)HIPEs was achieved using a dimethoxymethane external crosslinker to ‘knit’ together aromatic groups within the polymers using FriedelCrafts alkylation. By varying the amount of divinylbenzene (DVB) in the HIPE templates and subsequent polymers, the BET surface area and micropore volume of the hypercrosslinked analogues can be varied systematically, allowing for the production of carbon foams, or ‘carboHIPEs’, with varied surface areas, micropore volumes and pore-size distributions. The carboHIPEs retain the emulsion-templated macropores of the original polyHIPE, display excellent electrical conductivities and have surface areas of up to 417 m2/g, all the while eliminating the need for inorganic templates. The use of emulsion templates allows for pourable, mouldable precursors to designable carbonaceous materials.
Anthony DB, bismarck A, blaker JJ, et al., 2016, Development of novel composites through fibre and interface/interphase modification, 37th Risø International Symposium on Materials Science, Publisher: IOP, Pages: 012001-012001, ISSN: 1757-8981
We show how fibre/matrix interface (or interphase) modification can be used to develop a range of novel carbon fibre reinforced polymer (CFRP) composites that open up new applications far beyond those of standard CFRPs. For example, composites that undergo pseudo-ductile failure have been created through laser treatment of carbon fibres. Composites manufactured with thermo-responsive interphases can undergo significant reductions in stiffness at elevated temperatures. Additionally, structural supercapacitors have been developed through a process that involves encapsulating carbon fibres in carbon aerogel.
De Luca H, Anthony DB, Qian H, et al., 2016, Non-damaging and scalable carbon nanotube synthesis on carbon fibres, ECCM17 - 17th European Conference on Composite Materials
The growth of carbon nanotubes (CNTs) on carbon fibres (CFs) to produce a hierarchical fibre with two differing reinforcement length scales, in this instance nanometre and micrometre respectively, is considered a route to improve current state-of-the-art fibre reinforced composites . The scalable production of carbon nanotube-grafted-carbon fibres (CNT-g-CFs) has been limited due to high temperatures, the use of flammable gases and the requirement of inert conditions for CNT synthesis, whist (ideally) maintaining underlying original substrate mechanical properties. Here, the continuous production of CNT-g-CF is demonstrated in an open chemical vapour deposition (CVD) reactor, crucially, whilst retaining the tensile properties of the carbon fibres. As synthesised CNTs have a diameter of sub 20 nm and length ca. 120 nm, which are predicted to provide ideal fibre reinforcement in composites by retaining optimal composite fibre volume fraction (60%), whilst improving interfacial bonding of the matrix and reinforcement [1, 2]. Mild processing techniques enable this modified CVD process to be fully compatible with industrial practices, and have the potential to generate large volumes of hierarchical CNT-g-CF material.
Anthony DB, Grail G, Bismarck A, et al., 2016, Exploring the tensile response in small carbon fibre composite bundles, ECCM17 - 17th European Conference on Composite Materials
Small composite bundles, AS4 carbon fibre epoxy, with a restricted number of reinforcing fibres, ca. 20, showed a progressive failure when tested in tension. In-situ acoustic emission observations under tensile load reveal that numerous fibres fail before ultimate failure of the small composite bundle, suggesting that isolated and individual fibre failures occur without compromising the integrity of the neighboring fibres or the small composite bundle’s overall mechanical performance. The average strength of the carbon fibres in small composite bundles was 9.6% higher than in standard lab-scale composite specimens using the same fibre type.
Blaker JJ, Anthony DB, Tang G, et al., 2016, Property and shape modulation of carbon fibers using lasers, ACS Applied Materials & Interfaces, Vol: 8, Pages: 16351-16358, ISSN: 1944-8244
An exciting challenge is to create unduloid-reinforcing fibers with tailored dimensions to produce synthetic composites with improved toughness and increased ductility. Continuous carbon fibers, the state-of-the-art reinforcement for structural composites, were modified via controlled laser irradiation to result in expanded outwardly tapered regions, as well as fibers with Q-tip (cotton-bud) end shapes. A pulsed laser treatment was used to introduce damage at the single carbon fiber level, creating expanded regions at predetermined points along the lengths of continuous carbon fibers, whilst maintaining much of their stiffness. The range of produced shapes was quantified and correlated to single fiber tensile properties. Mapped Raman spectroscopy was used to elucidate the local compositional and structural changes. Irradiation conditions were adjusted to create a swollen weakened region, such that fiber failure occurred in the laser treated region producing two fiber ends with outwardly tapered ends. Upon loading the tapered fibers allow for viscoelastic energy dissipation during fiber pull-out by enhanced friction as the fibers plough through a matrix. In these tapered fibers, diameters were locally increased up to 53%, forming outward taper angles of up to 1.8°. The tensile strength and strain to failure of the modified fibers were significantly reduced, by 75% and 55%, respectively, ensuring localization of the break in the expanded region; however, the fiber stiffness was only reduced by 17%. Using harsher irradiation conditions, carbon fibers were completely cut, resulting in cotton-bud fiber end shapes. Single fiber pull-out tests performed using these fibers revealed a 6.75 fold increase in work of pull-out compared to pristine carbon fibers. Controlled laser irradiation is a route to modify the shape of continuous carbon fibers along their lengths, as well as to cut them into controlled lengths leaving tapered or cotton-bud shapes.
Woodward RT, Fam DWH, Anthony DB, et al., 2016, Hierarchically porous carbon foams from pickering high internal phase emulsions, Carbon, Vol: 101, Pages: 253-260, ISSN: 0008-6223
Carbon foams were produced from a macroporous poly(divinylbenzene) (poly(DVB) precursor, synthesized by polymerizing the continuous but minority phase of water-in-oil high internal phase emulsions (HIPEs) stabilized by molecular and/or particulate emulsifiers. Both permeable and non-permeable hierarchically porous carbon foams, or ‘carboHIPEs’, were prepared by carbonization of the resulting macroporous polymers at 800 °C. The carbon yields were as high as 26 wt.% of the original polymer. CarboHIPEs retain the pore structure of the macroporous polymer precursor, but with surface areas of up to 505 m2/g and excellent electrical conductivities of 81 S/m. Contrary to some previous reports, the method does not require further modification, such as sulfonation or additional crosslinking of the polyHIPE prior to carbonization, due to the inherently crosslinked structure of poly(DVB). The use of a pourable, aqueous emulsion-template enables simple moulding, minimises waste and avoids the strong acid treatments used to remove many conventional solid-templates. The retention of the macroporous structure is coupled with the introduction of micropores during carbonization, producing hierarchically porous carboHIPEs, suitable for a wide range of applications as sorbents and electrodes.
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