Imperial College London

Prof Milo Shaffer

Faculty of Natural SciencesDepartment of Chemistry

Professor of Materials Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 5825m.shaffer Website

 
 
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Assistant

 

Mr John Murrell +44 (0)20 7594 2845

 
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Location

 

401BMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

327 results found

Shaw C, Anthony D, Hamerton I, Shaffer Met al., 2024, Bicontinuous silica-epoxy nanocomposites by aerogel infusion, Composites Part A: Applied Science and Manufacturing, Vol: 182, ISSN: 1359-835X

Interpenetrated, bicontinuous nanocomposites are formed by fully infusing monolithic mesoporous silica (silica aerogel) with epoxy resin. The long-range connectivity of the silica network facilitates direct load transfer and enforces sample homogeneity. The silica networks are prepared using sol–gel chemistry, informed by new phase diagrams, adapted to maximise reinforcement content in the subsequent bicontinuous composite. The infusibility of the aerogels is correlated to pore characteristics determined by gas sorption, as a function of silica aerogel density. Silica reinforcement loadings of up to 22 silica vol.% are fully consolidated, with only a modest reduction in glass transition temperature and no change in cure conditions. The reinforcement improves both hardness (+23 %) and reduced modulus (+17 %) of the baseline resin. These properties increase with aerogel content via a power law relationship which demonstrates the direct role of the connected silica phase as a reinforcing network and motivates future studies to extend the applicable range.

Journal article

Jiang Q, Otáhalová V, Burré V, Leese HS, Shaffer MSP, Hahn R, Menner A, Bismarck Aet al., 2024, Variable capacity polymer based energy harvesters with integrated macroporous elastomer springs, Nano Energy, Vol: 124, ISSN: 2211-2855

We introduce a manufacturing concept of variable capacity energy harvesters consisting of macroporous springs integrated within a conducting silicone rubber and dielectric. Printing and polymerising emulsion templates resulted in macroporous spring elements, which were coated with conducting silicone rubber to maintain the active contact surface. By increasing size and number of these springs, the capacitance change of the energy harvesters during compression and recovery increased from 0.4 nF/cm2 to 0.8 nF/cm2. During cyclic loading with 30 N at 2 Hz, the energy harvesters with macroporous springs delivered a power density of 0.58 µW/cm2 at a bias voltage of 50 V, which was 25 times higher than the control without springs. The energy harvesters provided a constant power output over three hours of cyclic loading (21,600 cycles), indicating their structural stability and the durability of the macroporous springs.

Journal article

Wisnom MR, Pimenta S, Shaffer MSP, Robinson P, Potter KD, Hamerton I, Czél G, Jalalvand M, Fotouhi M, Anthony DB, Yu H, Longana ML, Wu X, Bismarck Aet al., 2024, High performance ductile and pseudo-ductile polymer matrix composites: a review, Composites Part A: Applied Science and Manufacturing, Vol: 181, ISSN: 1359-835X

The ability of fibre reinforced composites to deform with a non-linear stress–strain response and gradual, rather than sudden, catastrophic failure is reviewed. The principal mechanisms by which this behaviour can be achieved are discussed, including ductile fibres, progressive fibre fracture and fragmentation, fibre reorientation, and slip between discontinuous elements. It is shown that all these mechanisms allow additional strain to be achieved, enabling a yield-like behaviour to be generated. In some cases, the response is ductile and in others pseudo-ductile. Mechanisms can also be combined, and composites which give significant pseudo-ductile strain can be produced. Notch sensitivity is reduced, and there is the prospect of increasing design strains whilst also improving damage tolerance. The change in stiffness or visual indications of damage can be exploited to give warning that strain limits have been exceeded. Load carrying capacity is still maintained, allowing continued operation until repairs can be made. Areas for further work are identified which can contribute to creating structures made from high performance ductile or pseudo-ductile composites that fail gradually.

Journal article

Cowie BE, Mears KL, S'ari M, Lee JK, Briceno de Gutierrez M, Kalha C, Regoutz A, Shaffer MSP, Williams CKet al., 2024, Exploiting Organometallic Chemistry to Functionalize Small Cuprous Oxide Colloidal Nanocrystals., J Am Chem Soc, Vol: 146, Pages: 3816-3824

The ligand chemistry of colloidal semiconductor nanocrystals mediates their solubility, band gap, and surface facets. Here, selective organometallic chemistry is used to prepare small, colloidal cuprous oxide nanocrystals and to control their surface chemistry by decorating them with metal complexes. The strategy is demonstrated using small (3-6 nm) cuprous oxide (Cu2O) colloidal nanocrystals (NC), soluble in organic solvents. Organometallic complexes are coordinated by reacting the surface Cu-OH bonds with organometallic reagents, M(C6F5)2, M = Zn(II) and Co(II), at room temperature. These reactions do not disrupt the Cu2O crystallinity or nanoparticle size; rather, they allow for the selective coordination of a specific metal complex at the surface. Subsequently, the surface-coordinated organometallic complex is reacted with three different carboxylic acids to deliver Cu-O-Zn(O2CR') complexes. Selective nanocrystal surface functionalization is established using spectroscopy (IR, 19F NMR), thermal gravimetric analyses (TGA), transmission electron microscopy (TEM, EELS), and X-ray photoelectron spectroscopy (XPS). Photoluminescence efficiency increases dramatically upon organometallic surface functionalization relative to that of the parent Cu2O NC, with the effect being most pronounced for Zn(II) decoration. The nanocrystal surfaces are selectively functionalized by both organic ligands and well-defined organometallic complexes; this synthetic strategy may be applicable to many other metal oxides, hydroxides, and semiconductors. In the future, it should allow NC properties to be designed for applications including catalysis, sensing, electronics, and quantum technologies.

Journal article

Nguyen S, Anthony DB, Katafiasz T, Qi G, Razavi S, Senokos E, Greenhalgh ES, Shaffer MSP, Kucernak ARJ, Linde Pet al., 2024, Manufacture and characterisation of a structural supercapacitor demonstrator, Composites Science and Technology, Vol: 245, ISSN: 0266-3538

Structural power composites, a class of multifunctional materials, may facilitate lightweighting and accelerate widespread electrification of sustainable transportation. In the example considered in this paper, structural power composite fuselage components could provide power to open aircraft doors in an emergency and thus reduce or eliminate the mass and volume needed for supercapacitors currently mounted on the doors. To demonstrate this concept, an 80 cm long multifunctional composite C-section beam was designed and manufactured, which powered the opening and closing of a desktop-scale composite aircraft door. Twelve structural supercapacitor cells were made, each 30 cm × 15 cm × 0.5 mm, and two stacks of four cells were integrated into the web of the beam by interleaving and encasing them with low-temperature-cure woven carbon fibre/epoxy prepreg. This article culminates by considering the engineering challenges that need to be addressed to realise structural power composite components, particularly in an aerospace context.

Journal article

Radhakrishnan A, Georgillas I, Hamerton I, Shaffer MSP, Ivanov DSet al., 2023, Manufacturing multi-matrix composites: out-of-vacuum bag consolidation, Journal of Manufacturing Science and Engineering, Vol: 145, ISSN: 0022-0817

The formation of porosity is a major challenge in any composite manufacturing process, particularly in the absence of vacuum assistance. Highly localized injection of polymer matrix into regions of interest in a dry preform is a route to manufacturing multi-matrix fiber-reinforced composites with high filler concentrations, which are otherwise difficult to achieve. Unlike traditional composites, such multi-matrix fiber-reinforced composite systems, which combine multiple resins in continuous form, offer improved structural performance around stress concentrators and multifunctional capabilities. As the process lacks vacuum assistance, porosity becomes a primary issue to be addressed. This paper presents a rheo-kinetic coupled rapid consolidation procedure for optimizing the quality of localized matrix patches. The procedure involves manufacturing trials and analytical consolidation models to determine the best processing program for minimal voidage in the patch. The results provide a step toward an efficient manufacturing process for the optimal design of multi-matrix composites without the need for complex vacuum bag arrangements, thus reducing cost and time while opening avenues to improve overall composite performance.

Journal article

Gargiuli JF, Board RG, Shaffer MSP, Hamerton Iet al., 2023, Evaluation of healable epoxy matrices as covalent adaptive networks in uniaxial compression, Reactive and Functional Polymers, Vol: 192, ISSN: 1381-5148

Vitrimers provide dynamic bonding that can allow a degree of self-healing capability in cross-linked resins. A commercial amine-cured epoxy resin, Prime 27, showed a compressive yield stress, measured in compression, of 88 ± 2 MPa and a compression modulus of 3.41 ± 0.03 GPa. This base resin was modified by incorporating various proportions of two commercial vitrimers, either Thioplast EPS35 (an aliphatic epoxy-terminated polysulfide) or Vitrimax T130 (an imine-cured DGEBA epoxy resin). The addition of increasing amounts of Thioplast EPS35 into the resin led to a rapid drop in the glass transition temperature of the matrices and also a reduction in compressive performance. After an initial test in quasi-static, uniaxial compression, samples containing vitrimers were heated for 1 h at 100 °C and then subjected to a second compression test; all of the matrices loaded with Thioplast EPS35 were able to recover their full initial compression performance. Addition of increasing amounts of Vitrimax T130 to the same commercial epoxy resin did not cause any change in its glass transition temperature. However, after initial compression testing, followed by heating (1 h at 100 °C), only the formulation containing 40 wt% Vitrimax T130-loaded matrix regained its full initial compressive performance. Optimal results in terms of healing capability, measured as the recovery of the initial compression performance during a second identical test, following a heating step, were achieved by incorporating 10 wt% of EPS35 or 40 wt% Vitrimax T130, with little to no drop in glass transition temperature. For these selected formulations, the incorporation of 10% Thioplast EPS35 in Prime 27 gave a yield stress of 83 ± 2 MPa and a compression modulus of 3.13 ± 0.02 GPa, while the addition of 40% Vitrimax T130 gave a yield stress of 79 ± 2 MPa and a compression modulus of 3.30 ± 0.02 GPa.

Journal article

Hwang GB, Stent J, Noimark S, Heo KJ, MacRobert AJ, Kay CWM, Salvadori E, Williams CK, Pike SD, Shaffer MSP, Allan E, Parkin IPet al., 2023, White light-activated bactericidal coating using acrylic latex, crystal violet, and zinc oxide nanoparticles, Materials Advances, Vol: 5, Pages: 259-266

In this study, a white light-activated bactericidal coating consisting of acrylic latex, zinc oxide nanoparticles (ZnO NPs) and crystal violet (CV) was produced through a two-step dipping process. CV molecules and ZnO NPs were incorporated into an acrylic latex coating deposited onto a glass substrate. After the incorporation, the colour of the coating surface changed to purple from colourless and XPS sputtering analysis showed the existence of ZnO NPs within the coating. In a bactericidal test, the CV dyed samples showed an intrinsic bactericidal activity (0.7-0.88 log reduction in viable bacteria number) against S. aureus whereas it was not observed on E. coli in the dark. Upon white light irradiation (light intensity: 512 lux), the bactericidal activity of the CV-dyed sample was significantly enhanced. Compared to the control, the CV-dyed samples showed 1.16-2.51 log reduction against both bacterial strains in white light. In terms of the testing against S. aureus in white light, ZnO NPs addition into the CV-dyed sample showed enhanced bactericidal activity. The bactericidal activity of the CV-dyed sample with ZnO NPs was 1.34 log higher than the CV-dyed sample. Based on data obtained from TR-EPR spectroscopy, it is speculated that the addition of ZnO NPs into the dye induces an alternative photoredox pathway, resulting in more generation of reactive oxygen species lethal to bacterial cells. It is expected that this technique could be used to transform a wide range of surfaces into bactericidal surfaces and contribute to maintaining low pathogen levels on hospital surfaces related to healthcare-associated infection.

Journal article

Gargiuli JF, Quino G, Board R, Griffith JC, Shaffer MSP, Trask RS, Hamerton Iet al., 2023, Examining the quasi-static uniaxial compressive behaviour of commercial high-performance epoxy matrices, Polymers, Vol: 15, ISSN: 2073-4360

Four commercial high-performance aerospace aromatic epoxy matrices, CYCOM®890, CYCOM®977-2, PR520, and PRISM EP2400, were cured to a standardised 2 h, 180 °C cure cycle and evaluated in quasi-static uniaxial compression, as well as by dynamic scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermoplastic toughened CYCOM®977-2 formulation displayed an overall increase in true axial stress values across the entire stress-strain curve relative to the baseline CYCOM®890 sample. The particle-toughened PR520 sample exhibited an overall decrease in true axial stress values past the yield point of the material. The PRISM EP2400 resin, with combined toughening agents, led to true axial stress values across the entire plastic region of the stress-strain curve, which were in line with the stress values observed with the CYCOM®890 material. Interestingly, for all formulations, the dilation angles (associated with the volume change during plastic deformation), recorded at 0.3 plastic strain, were close to 0°, with the variations reflecting the polymer structure. Compression data collected for this series of commercial epoxy resins are in broad agreement with a selection of model epoxy resins based on di- and tetra-functional monomers, cured with polyamines or dicarboxylic anhydrides. However, the fully formulated resins demonstrate a significantly higher compressive modulus than the model resins, albeit at the expense of yield stress.

Journal article

Li Y, Shaffer MSP, 2023, Confocal microscopy for in situ multi-modal characterization and patterning of laser-reduced graphene oxide, Advanced Functional Materials, Vol: 33, Pages: 1-13, ISSN: 1616-301X

Graphene oxide (GO) films can be readily prepared at wafer scale, then reduced to form graphene-based conductive circuits relevant to a range of practical device applications. Among a variety of reduction methods, laser processing has emerged as an important technique for localized reduction and patterning of GO films. In this study, the novel use of confocal microscopy is demonstrated for high-resolution characterization, in situ laser reduction, and versatile patterning of GO films. Multi-modal imaging and real-time tracking are performed with 405 and 488 nm lasers, enabling large-area direct observation of the reduction progress. Using image analysis to cluster flake types, the different stages of reduction can be attributed to thermal transfer and accumulation. Delicate control of the reduction process over multiple length scales is illustrated using millimeter-scale stitched patterns, micropatterning of single flakes, and direct writing conductive 2D wires with sub-micrometer resolution (530 nm). The general applicability of the technique is shown, allowing fabrication of both conductive reduced graphene oxide (rGO) films (sheet resistance: 2.5 kOhm sq−1) and 3D microscale architectures. This simple and mask-free method provides a valuable tool for well-controlled and scalable fabrication of reduced GO structures using compact low-power lasers (< 5 mW), with simultaneous in situ monitoring and quality control.

Journal article

Cowie BE, Häfele L, Phanopoulos A, Said SA, Lee JK, Regoutz A, Shaffer MSP, Williams CKet al., 2023, Matched ligands for small, stable colloidal nanoparticles of copper, cuprous oxide and cuprous sulfide, Chemistry: A European Journal, Vol: 29, Pages: 1-18, ISSN: 0947-6539

This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2 O or Cu2 S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1-0.2 equivalents vs. [CuMes]z ) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2 CR1 ), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2 CR2 ) or di(thio)nonanoic acid, (HS2 CR1 ), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2 O is preferentially coordinated by carboxylate ligands and Cu2 S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection.

Journal article

Shaffer M, Moore J, Paineau E, Launois Pet al., 2023, Wet spinning imogolite nanotube fibres: an in situ process study, Nanoscale Advances, Vol: 5, Pages: 3376-3385, ISSN: 2516-0230

Imogolite nanotubes (INTs) form transparent aqueous nematic solutions, with strong birefringence and X-ray scatteringpower. They provide an ideal model system for studying the assembly of one-dimensional nanomaterials into fibres, as wellas offering interesting properties in their own right. Here, in-situ polarised optical microscopy is used to study the wetspinning of pure INTs into fibres, illustrating the influence of process variables during extrusion, coagulation, washing anddrying on both structure and mechanical properties. Tapered spinnerets were shown to be significantly more effective thanthin cylindrical channels for forming homogeneous fibres; a result related to simple capilliary rheology by fitting a shearthinning flow model. The washing step has a strong influence of structure and properties, combining the removal of residualcounter-ions and structural relaxation to produce a less aligned, denser and more networked structure; the timescales andscaling behviour of the processes are compared quantitatively. Both strength and stiffness are higher for INT fibres with ahigher packing fraction and lower degree of alignment, indicating the importance of forming a rigid jammed network totransfer stress through these porous, rigid rod assemblies. The electrostatically-stabilised, rigid rod INT solutions weresuccessfully cross-linked using multivalent anions, providing robust gels, potentially useful in other contexts.

Journal article

Asfaw HD, Kucernak A, Greenhalgh ES, Shaffer MSPet al., 2023, Electrochemical performance of supercapacitor electrodes based on carbon aerogel-reinforced spread tow carbon fiber fabrics, Composites Science and Technology, Vol: 238, ISSN: 0266-3538

Fabric-based supercapacitor electrodes were fabricated by embedding spread tow carbon fiber fabrics, in monolithic, bicontinuous carbon aerogels (CAG). The incorporation of CAG, at less than 30 wt%, increased the specific surface area of the CAG-CF fabric to above 230 m2 g−1 and the pore volume to about 0.35 cm3 g−1, orders of magnitude higher than that for the as-received carbon fibres. The presence of the CAG not only improves the electrochemical performance of the composite electrodes but may enhance the mechanical response due to the high stiffness of the aerogel structure. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance measurements were performed on symmetric supercapacitor cells consisting of two CAG-reinforced fabrics in an ionic liquid electrolyte. The specific capacitance of the symmetric supercapacitor was determined to be in the range 3–5 F g−1, considerably higher than that for the plain carbon fibers. Since optimum structural electrolytes are not yet available, this value was normalized to the total mass of both electrodes to place an upper bound on future structural supercapacitors using this spread tow CAG-CF system. The maximum specific energy and specific power, normalized to the total mass of the electrodes, were around 2.64 W h kg−1 and 0.44 kW kg−1, respectively. These performance metrics demonstrate that the thin CAG-modified spread tow fabrics are promising electrodes for future use in structural supercapacitors. In principle, in future devices, the reduced ply thickness offers both improved mechanical properties and shorter ion diffusion distance, as well as opportunities to fabricate higher voltage multicell assemblies within a given component geometry.

Journal article

Yang SM, Shaffer MSP, Brandt-Talbot A, 2023, High Lignin Content Carbon Fiber Precursors Wet-Spun from Low-Cost Ionic Liquid Water Mixtures, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 11, Pages: 8800-8811, ISSN: 2168-0485

Journal article

Valkova M, Nguyen S, Senokos E, Razavi S, Kucernak ARJ, Anthony DB, Shaffer MSP, Greenhalgh ESet al., 2023, Current collector design strategies: The route to realising scale-up of structural power composites, Composites Science and Technology, Vol: 236, Pages: 1-9, ISSN: 0266-3538

Multifunctional structural power composites, which combine mechanical load-bearing and electrochemical energy storage, will transform electric vehicle design. This work focuses on structural supercapacitors, based on carbon aerogel-modified carbon fibre electrodes with copper current collectors. In common with many structural power embodiments, scale-up of these devices is currently limited by large internal resistances and the mass associated with current collection. There is a trade-off between the overall resistive power loss and the additional mass for the current collector material. However, in these devices, mechanical integrity is provided by the structural electrodes, allowing a range of collector designs to be considered. Using finite element simulations, these current collection strategies are explored quantitatively across a range of design space variables. The key conductivity parameters were measured experimentally, using the best existing materials, to inform direct current conduction simulations of the electrode/current collector assembly. For the present device configuration, the performance trade-off is governed by the area of the current collector. The most effective near-term strategy for power loss mitigation lies in reducing the contact resistance; however, improvements can also be obtained by modifying the collector geometry. The findings of this paper can be generalised to other structural power composites and monofunctional energy storage devices, which are relevant in many mass-sensitive electrochemical applications.

Journal article

Senokos E, Anthony DB, Rubio N, Ribadeneyra MC, Greenhalgh ES, Shaffer MSPet al., 2023, Robust single‐walled carbon nanotube‐infiltrated carbon fiber electrodes for structural supercapacitors: from reductive dissolution to high performance devices, Advanced Functional Materials, Vol: 33, Pages: 1-11, ISSN: 1616-301X

Multifunctional electrodes for structural supercapacitors are prepared by vacuum infiltration of single-walled carbon nanotubes (SWCNTs) into woven carbon fibers (CFs); the use of reductive charging chemistry to form nanotubide solutions ensured a high degree of individualization. The route is highly versatile, as shown by comparing four different commercial nanotube feedstocks. In film form, the pure nanotubide networks (“buckypapers”) are highly conductive (up to 2000 S cm−1) with high surface area (>1000 m2 g−1) and great electrochemical performance (capacitance of 101 F g−1, energy density of 27.5 Wh kg−1 and power density of 135 kW kg−1). Uniformly integrating these SWCNT networks throughout the CF fabrics significantly increased electrical conductivity (up to 318 S cm−1), surface area (up to 196 m2 g−1), and in-plane shear properties, all simultaneously. The CNT-infiltrated CFs electrodes exhibited intrinsically high specific energy (2.6–4.2 Wh kg−1) and power (6.0–8.7 kW kg−1) densities in pure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) electrolyte. Multifunctional structural supercapacitors based on CNT-coated CFs offer a substantial increase in capacitive performance while maintaining the tensile mechanical properties of the as-received CF-based composite. This non-damaging approach to modify CFs with highly graphitic, high surface area nanocarbons provides a new route to structural energy storage systems.

Journal article

Greenhalgh ES, Nguyen S, Valkova M, Shirshova N, Shaffer MSP, Kucernak ARJet al., 2023, A critical review of structural supercapacitors and outlook on future research challenges, Composites Science and Technology, Vol: 235, Pages: 1-19, ISSN: 0266-3538

Structural composites and electrochemical energy storage underpin electrification of transportation, but advances in electric vehicles are shackled by parasitic battery mass. The emergence of structural power composites, multifunctional materials that simultaneously carry structural loads whilst storing electrical energy, promises dramatic improvements in effective performance Here, we assess the literature on structural supercapacitors, not only providing a comprehensive and critical review of the constituent (i.e., structural electrode, structural electrolyte and structural separator) developments, but also considering manufacture, characterisation, scale-up, modelling and design/demonstration. We provide a rigorous analysis of the multifunctional performance data reported in the literature, providing the reader with a detailed comparison between the different structural supercapacitor developments. We conclude with insights into the future research and adoption challenges for structural supercapacitors. There are several significant hurdles which must be addressed to mature this technology. These include development of a processable structural electrolyte; optimisation of current collection to facilitate device scale-up; identification of load-transmitting encapsulation solutions; standard protocols for characterisation and ranking of structural supercapacitors and; predictive multiphysics models for structural supercapacitors. Through addressing such issues, these emerging multifunctional materials will deliver a novel lightweighting strategy that can contribute to managing the ongoing climate crisis.

Journal article

Anthony DB, Nguyen SN, Qian H, Xu S, Shaw CMD, Greenhalgh ES, Bismarck A, Shaffer MSPet al., 2023, Silica aerogel infused hierarchical glass fiber polymer composites, Composites Communications, Vol: 39, Pages: 1-7, ISSN: 2452-2139

Hierarchical systems can address the matrix-dominated failures of structural fiber polymer composites. Here, a new synergistic hierarchical structure combines conventional structural glass fibers with a bi-continuous silica-based aerogel matrix; both pure-silica and organically-modified silicate aerogels are demonstrated. When infused with an epoxy matrix, this type of hierarchical architecture showed a marked improvement in mechanical properties: without any loss in modulus, both the compressive strength and the interlaminar shear strength increased by up to 27%, relative to the equivalent glass-fiber reinforced epoxy composite baseline. The bi-continuous network modification strategy uses industrially-relevant infusion techniques, at or near room temperature, and retains a similar final composite density (within 2%). The strategy presented here provides a versatile and readily applicable means to improve state-of-the art continuous fiber reinforced composite systems in compression and offers an opportunity to develop a new generation of composite materials.

Journal article

Gogoi R, De Luca F, Anthony D, Shaffer Met al., 2023, The effect of nacre-inspired coating on the tensile properties of carbon fibre composite, Carbon 2022 The World Conference on Carbon ‘Carbon for a Cleaner Future’

Conference paper

Shaw CMD, Anthony DB, Hamerton I, Shaffer MSPet al., 2023, BICONTINUOUS SILICA-EPOXY NANOCOMPOSITES

Monolithic mesoporous silica (silica aerogel) is presented as 3D continuous reinforcement for conventional thermoplastic matrices. Backfilling of the porous silica network with epoxy resin yields a bicontinuous material with interlocking silica and epoxy phases. Long range connectivity in the resulting silica reinforcement will better facilitate load transfer within the nanocomposite whilst ensuring uniform silica dispersion. This reinforcing structure may increase stiffness whilst retaining the toughness of the epoxy resin. A stiffer matrix will better resist fibre micro-buckling when applied to unidirectional fibre composite materials leading to an overall improvement in compressive strength. A pre-formed monolithic reinforcement avoids the undesirable viscosity and agglomeration effects seen for dispersed nanoparticulate fillers allowing potentially higher weight loadings of silica reinforcement. Silica content is instead limited only by the ability of the porous silica aerogel network to uptake epoxy resin. Therefore, a mesoporous silica precursor of high envelope density (> 0.2 g.cm-3) with a sufficiently open pore structure for epoxy-backfilling is required.

Conference paper

Gogoi R, Anthony DB, Eichhorn SJ, Shaffer MSPet al., 2023, THE EFFECT OF NACRE-INSPIRED COATING ON THE COMPRESSION BEHAVIOUR OF CARBON FIBRE COMPOSITE

The failure mechanism of unidirectional fibre-reinforced polymers in compression is complex and relates to a progression of failure from fibre micro buckling upwards across multiple coupled length scales. The initial fibre instability relates to the shear properties of the matrix and the alignment (or waviness) of the fibre. The initiation may also be affected by local composition/fibre volume fractions, matrix defects (for instance voids), or geometric features of the specimen/component. The use of surface-modified carbon fibres could improve the longitudinal compressive performance of composites by suppressing or delaying the formation of kink bands. A nanostructured hierarchical coating inspired by the brick-and-mortar structure of natural nacre was deposited around each individual fibre in a tow. The nanostructured coating contains layered-double-hydroxide (LDH) platelets which are attached to the carbon fibre surface using a layer-by-layer deposition technique. LDH platelets were selected for their tuneable geometry and high surface charge density. Successful preparation of LDH platelets with an aspect ratio of 8 was confirmed by X-ray diffraction and transmission electron microscopy. The quality of the conformal LDH monolayer coating was assessed by scanning electron microscopy and preliminary results show the formation of a well-ordered LDH multi-layer coating. These coated fibre tows will be converted to unidirectional epoxy-matrix composites and tested in compression in future studies.

Conference paper

Almousa HA, De Luca H, Anthony DB, Greenhalgh ES, Bismarck A, Shaffer MSPet al., 2023, FAILURE OF CARBON NANOTUBE-GRAFTED CARBON FIBRE REINFORCED COMPOSITES BY SINGLE FIBRE PULL-OUT

Continuous production of carbon nanotube-grafted-carbon fibres (CNT-g-CFs) was performed in an open chemical vapour deposition reactor, and the resultant fibres were used in single-fibre pull-out tests to determine their interfacial properties with epoxy, nanoengineered epoxy, and polypropylene matrices. At a single CNT-g-CF level, the presence of uniform carbon nanotube (CNT) coverage, sub-550 nm length, has been shown to increase the interfacial shear strength (IFSS) by 26% (98.4 ± 7.2 MPa) when compared to the baseline unsized carbon fibre (77.9 ± 5.1 MPa) embedded in a commercial epoxy. The IFSS increased when combining CNT-g-CF with a 2 wt.% multiwall carbon nanotube loaded epoxy matrix to 32% (102.8 ± 6.7 MPa) compared to the same baseline. In a polypropylene matrix, the presence of uniform CNT coverage on the carbon fibre surface also led to an increase in IFSS by 39% (11.2 ± 2.1 MPa) when compared to the unsized carbon fibre/polypropylene baseline (8.1 ± 1.5 MPa).

Conference paper

De Luca HG, Anthony DB, Almousa HA, Greenhalgh ES, Bismarck A, Shaffer MSPet al., 2023, CARBON NANOTUBE-GRAFTED QUARTZ FIBERS AS PIEZORESISTIVE REINFORCEMENT ELEMENTS

The mechanical properties of fiber-reinforced composites depend on the properties of the fiber/matrix interface where stress concentrations dominate. Grafting of carbon nanotubes to produce a “hairy” or “fuzzy” carbon fiber creates hierarchical reinforcements, combining two different reinforcement length scales, in this instance micrometer and nanometer. This approach improves the interaction between fibers and polymer matrices, and can enhance thermal and electrical functionality of the final composite. Generally, hairy fiber production is limited to batch processes due to harsh synthesis conditions (e.g. high temperature, inert environment) inherent to chemical vapor deposition, and have only recently been scaled-up to continuous production. The development of hierarchical assemblies, which are the combination of reinforcements at different length scales for instance nanoscale and microscale, have shown promise as multifunctional and structural state-of-the-art materials. The concept of using carbon nano-reinforcements with macroscopic fibers (quartz in this occasion) can directly address the limitations of current composites architectures, e.g. catastrophic failure, limited fire retardancy properties, and poor electro-thermal performances. Continuous production of such hierarchical materials, as a result of research carried out at Imperial College London and the University of Vienna, allows nano-engineered composites to finally meet industry implementation prerequisites. These methods are also compatible with commercial fiber production lines, which is a significant step forward towards the creation of a new class of high performance composite materials. Carbon nanotube-grafted-quartz fibers with uniform 200 nm long carbon nanotubes improved interfacial shear strength of 12% over a commercially sized counterpart (pull-out tests) in an epoxy matrix. Quartz fiber reinforced composites are normally electrically insulating, yet the carbon nano

Conference paper

Woodgate CG, Trask RS, Shaffer MSP, Eichhorn SJet al., 2023, COMPRESSIVE CHARACTERISATION OF SINGLE CARBON FIBRES AND THEIR COMPOSITE INTERFACES VIA IN SITU RAMAN SPECTROSCOPY

A current design limiting aspect of unidirectional carbon fibre reinforced polymer composites is their lack of strength in compression compared to tensile loading. To improve the compressive performance of carbon fibre reinforced polymer, it is critical to understand how failure occurs at each constituent length scale. One way to achieve this is to produce model composites, which address this at the single fibre level. In this study, Raman spectroscopy is used as a stress-sensing technique to analyse the micromechanical response of a range of single carbon fibres in compressive loading. The experimental procedure to produce single fibre compressive stress-strain curves for two high modulus carbon fibres are reported and discussed. An additional technique to utilise Raman spectroscopy to carry out point-to-point, spatially resolved stress mapping a long a length of fibre, from which interfacial shear stress characteristics can be derived is reported. The experimental setup has simpler sample design and preparation methods than other single fibre compression testing techniques, whilst being versatile in the measurements that can be obtained from various carbon fibre types.

Conference paper

Govada L, Rubio N, Saridakis E, Balaskandan K, Leese HS, Li Y, Wang B, Shaffer MSP, Chayen Net al., 2022, Graphene-based nucleants for protein crystallization, Advanced Functional Materials, Vol: 32, ISSN: 1616-301X

Protein crystallization remains a major bottleneck for the determination of high resolution structures. Nucleants can accelerate the process but should ideally be compatible with high throughput robotic screening. Polyethylene glycol grafted (PEGylated) graphenes can be stabilized in water providing dispensable, nucleant systems. Two graphitic feedstocks are exfoliated and functionalized with PEG using a non-destructive, scalable, chemical reduction method, delivering good water dispersibility (80 and 750 µg mL−1 for large and small layers, respectively). The wide utility of these nucleants has been established across five proteins and three different screens, each of 96 conditions, demonstrating greater effectiveness of the dispersed PEGylated graphenes. Smaller numbers of larger, more crystalline flakes consistently act as better protein nucleants. The delivered nucleant concentration is optimized (0.1 mg mL−1 in the condition), and the performance benchmarked against existing state of the art, molecularly imprinted polymer nucleants. Strikingly, graphene nucleants are effective even when decreasing both the nucleant and protein concentration to unusually low concentrations. The set-up to scale-up nucleant production to liter volumes can provide sufficient material for wide implementation. Together with the optimized crystallization conditions, the results are a step forward toward practical synthesis of a readily accessible “universal” nucleant.

Journal article

Ishfaq A, Nguyen S, Greenhalgh ES, Shaffer MSP, Kucernak ARJ, Asp LE, Zenkert D, Linde Pet al., 2022, Multifunctional design, feasibility and requirements for structural power composites in future electric air taxis, Journal of Composite Materials, Vol: 57, Pages: 817-828, ISSN: 0021-9983

This study investigates the viability of implementing multifunctional structural power composites in a four-seater air taxi, the CityAirbus. For a given specific energy of the power source, the cruise endurance can be approximately doubled by using structural power composites as opposed to conventional batteries. Replacing all the eligible composite mass and batteries with structural power composites can reduce the CityAirbus weight by 25%. To achieve the current design performance, the minimum required elastic modulus, strength, specific energy and power for the structural power composite are 54 GPa, 203 MPa, 74 Wh/kg and 376 W/kg, respectively: current state-of-the-art structural power composites are now approaching this level of performance. Hence, structural power composites are considered feasible for adoption in the urban air mobility sector and have the potential to improve endurance and facilitate commercialization. This paper also discusses several key challenges that must be addressed to realize the adoption of structural power composites in future electric air taxis.

Journal article

Rubio N, Suter T, Rana Z, Clancy AJ, Masuda S, Au H, Coulter G, Sirisinudomkit P, McMillan PF, Howard CA, Mattevi C, Brett DJL, Shaffer MSPet al., 2022, Platinum deposition on functionalised graphene for corrosion resistant oxygen reduction electrodes, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 10, Pages: 20121-20127, ISSN: 2050-7488

Journal article

Bayazit MK, Yau HC, Leese H, Lee WJ, Shaffer MSPet al., 2022, Mono-Acetylenes as New Crosslinkers for All-Carbon Living Charge Carbon Nanotubide Organogels, CHEMISTRYSELECT, Vol: 7, ISSN: 2365-6549

Journal article

Wang J, Anthony DB, Fuentes CA, De Luca HG, Zhang D, Bismarck A, Van Vuure AW, Shaffer MSP, Seveno Det 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.

Journal article

Yousefi N, Fisher SJ, Burgstaller C, Shaffer MSP, Bismarck Aet al., 2022, Hierarchical carbon fibre composites incorporating high loadings of carbon nanotubes, Composites Science and Technology, Vol: 222, ISSN: 0266-3538

Uncured solid bisphenol-A epoxy resins containing up to 20 wt% carbon nanotubes (CNTs) were prepared usingmelt blending in a high shear mixer. The extrudate was ground to produce fine nanocomposite (NC) powders.This simple method produced well-dispersed NC, with CNT agglomerate sizes below 1 μm. Consolidated NCsdisplayed improved tensile moduli and strengths up to 3.3 GPa (+32%) and 78 MPa (+19%), respectively at 15wt% CNT, compared to the pure cured epoxy matrix. The relatively high Tg of 39 ◦C for the uncured NC powderssimplified the manufacture of composite prepregs using wet powder impregnation. The prepregs were laminatedinto hierarchical carbon fibre reinforced composites with improved through-thickness properties. Interlaminarshear strength improved for intermediate CNT loadings in the matrix up to 65 MPa (10 wt% CNT, +19%) butdecreased at higher concentrations. Compression moduli remained constant irrespectively of CNT loading butcompression strength increased with a CNT loading of 2.5 wt% to 772 MPa (+31%). The mechanical propertiesof the hierarchical composites reflect good consolidation (void content <3%) and excellent fibre alignment(<±0.8◦). In addition to the improved mechanical properties, incorporation of CNTs improved the through-thickness electrical conductivity up to 115 S/m

Journal article

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