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

 

M221Royal College of ScienceSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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277 results found

Basma NS, Headen TF, Shaffer MSP, Skipper NT, Howard CAet al., 2018, Local structure and polar order in liquid N-Methyl-2-pyrrolidone (NMP), Journal of Physical Chemistry B, Vol: 122, Pages: 8963-8971, ISSN: 1520-5207

N-Methyl-2-pyrrolidone (NMP) is an exceptional solvent, widely used in industry and for nanomaterials processing. Yet despite its ubiquity, its liquid structure, which ultimately dictates its solvation properties, is not fully known. Here, neutron scattering is used to determine NMP’s structure in unprecedented detail. Two dominant nearest-neighbor arrangements are found, where rings are parallel or perpendicular. However, compared with related solvents, NMP has a relatively large population of parallel approaches, similar only to benzene, despite its nonaromaticity and the presence of the normally structure-reducing methyl group. This arrangement is underpinned by NMP’s dipole moment, which has a profound effect on its structure: nearest-neighbor molecules arrange in an antiparallel but offset fashion. This polar-induced order extends beyond the first solvation shell, resulting in ordered trimers that reach the nanometer range. The degree of order and balance of interactions rationalize NMP’s high boiling point and versatile capabilities to solvate both charged and uncharged species.

Journal article

Jia J, White ER, Clancy AJ, Rubio N, Suter T, Miller TS, McColl K, McMillan PF, Brázdová V, Corà F, Howard CA, Law RV, Mattevi C, Shaffer MSPet al., 2018, Fast exfoliation and functionalisation of two-dimensional crystalline carbon nitride by framework charging, Angewandte Chemie, Vol: 57, Pages: 12656-12660, ISSN: 1521-3757

Two-dimensional (2D) layered graphitic carbon nitride (gCN) nanosheets offer intriguing electronic and chemical properties. However, the exfoliation and functionalisation of gCN for specific applications remain challenging. We report a scalable one-pot reductive method to produce solutions of single- and few-layer 2D gCN nanosheets with excellent stability in a high mass yield (35 %) from polytriazine imide. High-resolution imaging confirmed the intact crystalline structure and identified an AB stacking for gCN layers. The charge allows deliberate organic functionalisation of dissolved gCN, providing a general route to adjust their properties.

Journal article

Hart M, Chen J, Michaelides A, Sella A, Shaffer MSP, Salzmann CGet al., 2018, One-dimensional arsenic allotropes: Polymerization of yellow arsenic inside single-wall carbon nanotubes, Angewandte Chemie - International Edition, Vol: 57, Pages: 11649-11653, ISSN: 0570-0833

The pnictogen nanomaterials, including phosphorene and arsenene, display remarkable electronic and chemical properties. Yet, the structural diversity of these main group elements is still poorly explored. Here we fill single‐wall carbon nanotubes with elemental arsenic from the vapor phase. Using electron microscopy, we find chains of highly reactive As4 molecules as well as two new one‐dimensional allotropes of arsenic: a single‐stranded zig‐zag chain and a double‐stranded zig‐zag ladder. These linear structures are important intermediates between the gas‐phase clusters of arsenic and the extended sheets of arsenene. Raman spectroscopy indicates weak electronic interaction between the arsenic and the nanotubes which implies that the formation of the new allotropes is driven primarily by the geometry of the confinement. The relative stabilities of the new arsenic structures are estimated computationally. Band‐gap calculations predict that the insulating As4 chains become semiconducting, once converted to the zig‐zag ladder, and form a fully metallic allotrope of arsenic as the zig‐zag chain.

Journal article

Hart M, Chen J, Michaelides A, Sella A, Shaffer MSP, Salzmann CGet al., 2018, One-Dimensional Arsenic Allotropes: Polymerization of Yellow Arsenic Inside Single-Wall Carbon Nanotubes, Angewandte Chemie, Vol: 130, Pages: 11823-11827, ISSN: 0044-8249

Journal article

Javaid A, Ho KKC, Bismarck A, Steinke JHG, Shaffer MSP, Greenhalgh ESet al., 2018, Improving the multifunctional behaviour of structural supercapacitors by incorporating chemically activated carbon fibres and mesoporous silica particles as reinforcement, JOURNAL OF COMPOSITE MATERIALS, Vol: 52, Pages: 3085-3097, ISSN: 0021-9983

Journal article

Anthony DB, Sui X, Kellersztein I, De Luca H, White E, Wagner HD, Greenhalgh E, Bismarck A, Shaffer Met 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.

Journal article

Shaffer MSP, Clancy A, Skipper N, Howard C, Bayazit MK, Hodge Set al., 2018, Charged carbon nanomaterials: the redox chemistries of fullerenes, carbon nanotubes, and graphenes, Chemical Reviews, Vol: 118, Pages: 7363-7408, ISSN: 1520-6890

Since the discovery of buckminsterfullerene over 30 years ago, sp2-hybridised carbon nanomaterials (including fullerenes, carbon nanotubes, and graphene) have stimulated new science and technology across a huge range of fields. Despite the impressive intrinsic properties, challenges in processing and chemical modification continue to hinder applications. Charged carbon nanomaterials (CCNs), formed via the reduction or oxidation of these carbon nanomaterials, facilitate dissolution, purification, separation, chemical modification, and assembly. This approach provides a compelling alternative to traditional damaging and restrictive liquid phase exfoliation routes. The broad chemistry of CCNs not only provides a versatile and potent means to modify the properties of the parent nanomaterial but also raises interesting scientific issues. This review focuses on the fundamental structural forms: buckminsterfullerene, single-walled carbon nanotubes, and single-layer graphene, describing the generation of their respective charged nanocarbon species, their interactions with solvents, chemical reactivity, specific (opto)electronic properties, and emerging applications.

Journal article

De Luca F, Clancy A, Rubio Carrero N, Anthony DB, De Luca H, Shaffer M, Bismarck Aet 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.

Journal article

Ellis T, Chiappi M, García-Trenco A, Al-Ejji M, Sarkar S, Georgiou TK, Shaffer MSP, Tetley TD, Schwander S, Ryan MP, Porter AEet al., 2018, Multimetallic microparticles increase the potency of rifampicin against intracellular mycobacterium tuberculosis, ACS Nano, Vol: 12, Pages: 5228-5240, ISSN: 1936-0851

Mycobacterium tuberculosis ( M.tb) has the extraordinary ability to adapt to the administration of antibiotics through the development of resistance mechanisms. By rapidly exporting drugs from within the cytosol, these pathogenic bacteria diminish antibiotic potency and drive the presentation of drug-tolerant tuberculosis (TB). The membrane integrity of M.tb is pivotal in retaining these drug-resistant traits. Silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs) are established antimicrobial agents that effectively compromise membrane stability, giving rise to increased bacterial permeability to antibiotics. In this work, biodegradable multimetallic microparticles (MMPs), containing Ag NPs and ZnO NPs, were developed for use in pulmonary delivery of antituberculous drugs to the endosomal system of M.tb-infected macrophages. Efficient uptake of MMPs by M.tb-infected THP1 cells was demonstrated using an in vitro macrophage infection model, with direct interaction between MMPs and M.tb visualized with the use of electron FIB-SEM tomography. The release of Ag NPs and ZnO NPs within the macrophage endosomal system increased the potency of the model antibiotic rifampicin by as much as 76%, realized through an increase in membrane disorder of intracellular M.tb. MMPs were effective at independently driving membrane destruction of extracellular bacilli located at the exterior face of THP1 macrophages. This MMP system presents as an effective drug delivery vehicle that could be used for the transport of antituberculous drugs such as rifampicin to infected alveolar macrophages, while increasing drug potency. By increasing M.tb membrane permeability, such a system may prove effectual in improving treatment of drug-susceptible TB in addition to M.tb strains considered drug-resistant.

Journal article

Thong A, Shaffer M, Horsfield AP, 2018, Rectification and negative differential resistance via orbital level pinning, Scientific Reports, Vol: 8, ISSN: 2045-2322

A donor-acceptor system, 4-thiophenyl-azafulleroid (4TPA-C60), is investigated at the point of HOMO/LUMO resonance and beyond to understand how negative differential resistance (NDR) features may be observed in such systems. Our previous investigation showed that charge transfer between the occupied and unoccupied states at resonance hindered crossing of the HOMO and LUMO levels, thus preventing the formation of an NDR feature. In this work, it is shown that the negative differential resistance feature of 4TPA-C60 can be tailored based on the couplings at the metal/molecule interface. Ab initio calculations show that limited charge extraction from atomically sharp contacts results in a HOMO-LUMO pinning effect which delays the onset of the NDR feature. Subsequent unpinning of the states can only occur when additional charge extraction channels enter the bias window, highlighting an important role which non-frontier states play in charge transport. The proposed charge transfer mechanism is then exploited by introducing a fluorine atom into the C60 cage to tune the energies of the acceptor, and narrow the width of the current peak. These findings not only demonstrate the importance of the metal/molecule interface in the design of molecular electronic architectures but also serve to inform future design of molecular diodes and RTDs.

Journal article

Fisher SJ, Shaffer M, 2018, Rapid quantitative mapping of multi-walled carbon nanotube concentration in nanocomposites, Composites Science and Technology, Vol: 160, Pages: 161-168, ISSN: 0266-3538

Inhomogeneous distributions of nanoparticles in polymer nanocomposites have a strong influence on final material properties. Quantitative methods to characterise particle dispersion are rarely applied but are critical for advancing understanding of material behaviour, developing accurate computer models, and optimizing processing. Two complementary quantitative methods were developed to map local concentration, based on Raman spectroscopy and simple optical absorbance, respectively. The approaches are demonstrated for a model multi-walled carbon nanotube (MWNT) epoxy nanocomposite, but should be widely applicable. Maps of absolute concentration can be produced with submicron resolution, allowing analysis of the uniformity of MWNT concentration distribution via the coefficient of variation. The two approaches correlate closely, providing validation of both methods. However, the optical absorbance approach is likely to be more practical, in most cases, as it uses a standard laboratory microscope to analyse large areas rapidly.

Journal article

Zhu Y, Radlauer MR, Schneiderman DK, Shaffer MSP, Hillmyer MA, Williams CKet al., 2018, Multiblock polyesters demonstrating high elasticity and shape memory effects, Macromolecules, Vol: 51, Pages: 2466-2475, ISSN: 0024-9297

Polyester block polymers containing polylactide have garnered significant attention as renewable, degradable alternatives to traditional elastomers. However, the low glass transition of the PLA blocks limits the upper-use temperatures of the resulting elastomers. To improve the thermal performance, we explore a series of multiblock polyesters composed of poly(ε-decalactone) (PDL) and poly(cyclohexene phthalate) (PCHPE). These materials are prepared using switchable polymerization catalysis followed by chain extension. The strategy involves (i) alternating ring-opening copolymerization (ROCOP) of cyclohexene oxide and phthalic anhydride, (ii) ε-decalactone ring-opening polymerization (ROP), and (iii) diisocyanate coupling of the telechelic triblocks to increase molar mass. The resulting multiblock polyesters are amorphous, and the blocks are phase separated; glass transition temperatures are ∼−45 and 100 °C. They show thermal resistance to mass loss with Td5% ∼ 285 °C and higher upper use temperatures compared to alternative aliphatic polyesters. The nanoscale phase behavior and correlated mechanical properties are highly sensitive to the block composition. The sample containing PCHPE = 26 wt % behaves as a thermoplastic elastomer with high elongation at break (εb > 2450%), moderate tensile strength (σb = 12 MPa), and low residual strain (εr ∼ 4%). It shows elastomeric behavior from −20 to 100 °C and has a processing temperature range of ∼170 °C. At higher PCHPE content (59 wt %), the material has shape memory character with high strain fixation (250%) and recovery (96%) over multiple (25) recovery cycles. The multiblock polyesters are straightforward to prepare, and the methods presented here can be extended to produce a wide range of new materials using a other epoxides, anhydrides, and lactones. This first report on the thermal and mechanical properties highlights the significant

Journal article

De Luca F, Sernicola G, Bismarck A, Shaffer MSPet al., 2018, “Brick-and-Mortar” Nanostructured Interphase for Glass Fiber-Reinforced Polymer Composites, ACS Applied Materials and Interfaces, Vol: 10, Pages: 7352-7361, ISSN: 1944-8244

The fiber–matrix interface plays a critical role in determining composite mechanical properties. While a strong interface tends to provide high strength, a weak interface enables extensive debonding, leading to a high degree of energy absorption. Balancing these conflicting requirements by engineering composite interfaces to improve strength and toughness simultaneously still remains a great challenge. Here, a nanostructured fiber coating was realized to manifest the critical characteristics of natural nacre, at a reduced length scale, consistent with the surface curvature of fibers. The new interphase contains a high proportion (∼90 wt %) of well-aligned inorganic platelets embedded in a polymer; the window of suitable platelet dimensions is very narrow, with an optimized platelet width and thickness of about 130 and 13 nm, respectively. An anisotropic, nanostructured coating was uniformly and conformally deposited onto a large number of 9 μm diameter glass fibers, simultaneously, using self-limiting layer-by-layer assembly (LbL); this parallel approach demonstrates a promising strategy to exploit LbL methods at scale. The resulting nanocomposite interphase, primarily loaded in shear, provides new mechanisms for stress dissipation and plastic deformation. The energy released by fiber breakage in tension appear to spread and dissipate within the nanostructured interphase, accompanied by stable fiber slippage, while the interfacial strength was improved up to 30%.

Journal article

Kennedy OW, Coke ML, White ER, Shaffer MSP, Warburton PAet al., 2018, MBE growth and morphology control of ZnO nanobelts with polar axis perpendicular to growth direction, Materials Letters, Vol: 212, Pages: 51-53, ISSN: 0167-577X

In quasi-one-dimensional polar nanostructures the relative orientation of the long and polar axes will determine how the polarity of the nanostructure may be exploited for applications. Here we present the growth by molecular-beam epitaxy of quasi-1d ZnO nanostructures (specifically nanobelts) with the polar axis perpendicular to the growth axis. We demonstrate the control of nanostructure morphology by growth temperature. Our work represents a key milestone towards the development of future polarization-engineered oxide heterostructures embedded in quasi-1d nanodevices.

Journal article

Leung AHM, Pike SD, Clancy AJ, Yau HC, Lee WJ, Orchard KL, Shaffer MSP, Williams CKet al., 2018, Layered zinc hydroxide monolayers by hydrolysis of organozincs, CHEMICAL SCIENCE, Vol: 9, Pages: 2135-2146, ISSN: 2041-6520

2D inorganic materials and their exfoliated counterparts are both of fundamental interest and relevant for applications including catalysis, electronics and sensing. Here, a new bottom-up synthesis route is used to prepare functionalised nanoplatelets, in apolar organic solvents, via the hydrolysis of organometallic reagents; the products can be prepared in high yield, at room temperature. In particular, a series of layered zinc hydroxides, coordinated by aliphatic carboxylate ligands, were produced by the hydrolysis of diethyl zinc and zinc carboxylate mixtures, optimally at a molar ratio of [COOR]/[Zn] = 0.6. Layered zinc hydroxides coordinated by oleate ligands form high concentration solutions of isolated monolayers (3 nm thick x ∼ 26 nm) in apolar organic solvents (up to 23 mg mL−1 in toluene), as confirmed by both atomic force and transmission electron microscopies of deposited species. The high solubility of the product allows the synthetic pathway to be monitored directly in situ through 1H NMR spectroscopy. The high solubility also provides a route to solution deposition of active functional materials, as illustrated by the formation of nanoporous films of optically transparent porous zinc oxide (1 μm thickness) after annealing at 500 °C. This new organometallic route to 2D materials obviates common complications of top-down exfoliation syntheses, including sonochemical-degradation and low yields of aggregated polydispersed layers, and may potentially be extended to a wide range of systems.

Journal article

Au H, Rubio N, Shaffer MSP, 2018, Brominated graphene as a versatile precursor for multifunctional grafting, Chemical Science, Vol: 9, Pages: 209-217, ISSN: 2041-6520

A non-destructive and versatile chemical reduction method was used to dissolve and subsequently brominate few-layer graphene sheets (FLGs); the direct covalent attachment of bromine to the graphene framework was demonstrated by X-ray photoelectron spectroscopy (XPS). The brominated few-layer graphenes (FLG-Br) provide a convenient, stable, liquid-phase precursor, suitable for the synthesis of a variety of directly functionalised graphenes. As an example, the FLG-Br species was used to initiate atom transfer radical polymerisation (ATRP), to obtain poly(methyl methacrylate) (PMMA)-grafted graphene (FLG-PMMA), which was six times more dispersible in acetone than controls. In addition, the FLG-Br is active for nucleophilic substitution reactions, as illustrated by the preparation of methoxypolyethylene glycol (mPEG)- and OH-substituted derivatives. The products were characterised by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), XPS and Raman spectroscopy. Grafting ratios (GR) for these polymer-grafted materials varied between 6 and 25%; even at these GRs, all graphene derivatives showed increased solubility in organic solvents.

Journal article

Woodward RT, Markoulidis F, De Luca F, Anthony D, Malko D, McDonald T, Shaffer M, Bismarck Aet 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.

Journal article

Garcia-Trenco A, Regoutz A, White ER, Payne DJ, Shaffer MSP, Williams CKet al., 2018, PdIn intermetallic nanoparticles for the hydrogenation of CO2 to methanol, Applied Catalysis B: Environmental, Vol: 220, Pages: 9-18, ISSN: 0926-3373

Direct hydrogenation of CO2 to methanol could offer significant environmental benefits, if efficient catalysts can be developed. Here, bimetallic Pd-In nanoparticles show good performance as catalysts for this reaction. Unsupported nanoparticles are synthesised by the thermal decomposition of Pd(acetate)2 and In(acetate)3 precursors in a high boiling point solvent (squalane), followed by reduction using dilute H2 gas (210 °C). Adjusting the ratio of the two metallic precursors allow access to 5–10 nm nanoparticles with different phase compositions, including metallic Pd(0), In2O3 and intermetallic PdIn. Liquid phase methanol synthesis experiments (50 bar, 210 °C, H2:CO2 = 3:1) identify the intermetallic PdIn nanoparticles as the most efficient. The catalysts exhibit around 70% higher methanol rates (normalised to the overall molar metal content) compared to the conventional heterogeneous Cu/ZnO/Al2O3 catalyst (900 and 540 μmol mmolPdInorCuZnAl−1 h−1, respectively). In addition, the optimum Pd/In catalyst shows an improved methanol selectivity over the whole temperature range studied (190–270 °C), reaching >80% selectivity at 270 °C, compared to only 45% for the reference Cu/ZnO/Al2O3 catalyst. Experiments showed an improvement in stability; the methanol production rate declined by 20% after 120 h run for the optimum PdIn-based compared with 30% for the Cu/ZnO/Al2O3 catalyst (after 25 h). The optimum catalyst consists of ∼8 nm nanoparticles comprising a surface In-enriched PdIn intermetallic phase as characterised by XRD, HR-TEM, STEM-EDX and XPS. Post-catalysis analysis of the optimum catalyst shows that the same PdIn bimetallic phase is retained with only a slight increase in the nanoparticle size.

Journal article

Finley JM, Yu H, Longana ML, Pimenta S, Shaffer MSP, Potter KDet al., 2017, Exploring the pseudo-ductility of aligned hybrid discontinuous composites using controlled fibre-type arrangements, Composites Part A: Applied Science and Manufacturing, Vol: 107, Pages: 592-606, ISSN: 1359-835X

Pseudo-ductility presents a potential means for preventing catastrophic failure in composite materials; large deformations will prevent brittle fracture and provide warning before final failure. This work explores how the pseudo-ductility and strength of aligned hybrid discontinuous composites can be controlled by manipulating the arrangement of different fibre types. Aligned carbon/glass hybrid specimens with different fibre arrangements are manufactured and tested using a modification to the High Performance Discontinuous Fibre (HiPerDiF) method. Experimental results are complemented by an improved virtual testing framework, which accurately captures the fracture behaviour of a range of hybrid discontinuous composite microstructures. With a randomly intermingled fibre arrangement as a baseline, a 27% increase in strength and a 44% increase in pseudo-ductility can be achieved when low elongation fibres are completely isolated from one-another. Results demonstrate that the HiPerDiF method is the current state-of-the-art for maximising the degree of intermingling and hence the pseudo-ductility of hybrid composites.

Journal article

Rocha VG, Garcia-Tunon E, Botas C, Markoulidis F, Feilden E, D'Elia E, Ni N, Shaffer M, Saiz Eet al., 2017, Multimaterial 3D Printing of Graphene-Based Electrodes for Electrochemical Energy Storage Using Thermoresponsive Inks, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 37136-37145, ISSN: 1944-8244

The current lifestyles, increasing population, and limited resources result in energy research being at the forefront of worldwide grand challenges, increasing the demand for sustainable and more efficient energy devices. In this context, additive manufacturing brings the possibility of making electrodes and electrical energy storage devices in any desired three-dimensional (3D) shape and dimensions, while preserving the multifunctional properties of the active materials in terms of surface area and conductivity. This paves the way to optimized and more efficient designs for energy devices. Here, we describe how three-dimensional (3D) printing will allow the fabrication of bespoke devices, with complex geometries, tailored to fit specific requirements and applications, by designing water-based thermoresponsive inks to 3D-print different materials in one step, for example, printing the active material precursor (reduced chemically modified graphene (rCMG)) and the current collector (copper) for supercapacitors or anodes for lithium-ion batteries. The formulation of thermoresponsive inks using Pluronic F127 provides an aqueous-based, robust, flexible, and easily upscalable approach. The devices are designed to provide low resistance interface, enhanced electrical properties, mechanical performance, packing of rCMG, and low active material density while facilitating the postprocessing of the multicomponent 3D-printed structures. The electrode materials are selected to match postprocessing conditions. The reduction of the active material (rCMG) and sintering of the current collector (Cu) take place simultaneously. The electrochemical performance of the rCMG-based self-standing binder-free electrode and the two materials coupled rCMG/Cu printed electrode prove the potential of multimaterial printing in energy applications.

Journal article

Clancy AJ, Serginson JM, Greenfield JL, Shaffer MSPet al., 2017, Systematic Comparison of Single-Walled Carbon Nanotube/ Poly(vinyl Acetate) Graft-to Reactions, Polymer, Vol: 133, Pages: 263-271, ISSN: 0032-3861

The covalent grafting of polymers to single-walled carbon nanotubes (SWCNTs) is widely used to improve solvent compatibility, as well as composite and functional performance. Here, three different graft-to strategies are directly compared, using azide, diazonium, and bromide terminated polymers, over four different molecular weights (oligomeric to 10 kDa) using specifically synthesized low polydispersity, end-group controlled poly(vinyl acetate) (PVAc) prepared by polymerisation using a bespoke protected-amine RAFT agent. Coupling of the bromo-polymer to reduced SWCNTs led to higher degrees of functionalisation (grafting ratios up to 68.9%) than the azide and diazonium grafting reactions, attributed to better initial dispersion of the pre-grafted SWCNTs. The use of higher molecular weight polymers led to a decrease in the total weight of polymer grafted, as the increase in per-polymer weight is more than offset by steric occlusion on the SWCNT surface. For these graft-to reactions, the dispersibility of grafted SWCNTs was found to depend most strongly on the polymer molecular weight, not total weight of grafted polymer or grafting chemistry, with an intermediate Mn∼5757 PVAc giving the best dispersibilities, at up to 118 mg L−1.

Journal article

Miller TS, Suter TM, Telford AM, Picco L, Payton OD, Russell-Pavier F, Cullen PL, Sella A, Shaffer MSP, Nelson J, Tileli V, McMillan PF, Howard CAet al., 2017, Single crystal, luminescent carbon nitride nanosheets formed by spontaneous dissolution, Nano Letters, Vol: 17, Pages: 5891-5896, ISSN: 1530-6984

A primary method for the production of 2D nanosheets is liquid-phase delamination from their 3D layered bulk analogues. Most strategies currently achieve this objective by significant mechanical energy input or chemical modification but these processes are detrimental to the structure and properties of the resulting 2D nanomaterials. Bulk poly(triazine imide) (PTI)-based carbon nitrides are layered materials with a high degree of crystalline order. Here, we demonstrate that these semiconductors are spontaneously soluble in select polar aprotic solvents, that is, without any chemical or physical intervention. In contrast to more aggressive exfoliation strategies, this thermodynamically driven dissolution process perfectly maintains the crystallographic form of the starting material, yielding solutions of defect-free, hexagonal 2D nanosheets with a well-defined size distribution. This pristine nanosheet structure results in narrow, excitation-wavelength-independent photoluminescence emission spectra. Furthermore, by controlling the aggregation state of the nanosheets, we demonstrate that the emission wavelengths can be tuned from narrow UV to broad-band white. This has potential applicability to a range of optoelectronic devices.

Journal article

Rubio Carrero N, Au H, Leese HS, Hu S, Clancy AJ, Shaffer MSPet al., 2017, Grafting from versus grafting to approaches for the functionalisation of graphene nanoplatelets with poly(methyl methacrylate), Macromolecules, Vol: 50, Pages: 7070-7079, ISSN: 0024-9297

Graphene nanoplatelets (GNP) were exfoliated using a nondestructive chemical reduction method and subsequently decorated with polymers using two different approaches: grafting from and grafting to. Poly(methyl methacrylate) (PMMA) with varying molecular weights was covalently attached to the GNP layers using both methods. The grafting ratios were higher (44.6% to 126.5%) for the grafting from approach compared to the grafting to approach (12.6% to 20.3%). The products were characterized using thermogravimetric analysis–mass spectrometry (TGA-MS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The grafting from products showed an increase in the grafting ratio and dispersibility in acetone with increasing monomer supply; on the other hand, due to steric effects, the grafting to products showed lower absolute grafting ratios and a decreasing trend with increasing polymer molecular weight. The excellent dispersibility of the grafting from functionalized graphene, 900 μg/mL in acetone, indicates an increased compatibility with the solvent and the potential to increase graphene reinforcement performance in nanocomposite applications.

Journal article

Buckley DJ, Hodge SA, De Marco M, Hu S, Anthony DB, Linden Cullen P, Skipper NT, Shaffer MSP, Howard CAet 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..

Journal article

Pike SD, Garcia-Trenco A, White ER, Leung AHM, Weiner J, Shaffer MSP, Williams CKet al., 2017, Colloidal Cu/ZnO catalysts for the hydrogenation of carbon dioxide to methanol: investigating catalyst preparation and ligand effects, Catalysis Science and Technology, Vol: 7, Pages: 3842-3850, ISSN: 2044-4753

The production of methanol from CO2 hydrogenation is a promising potential route to a renewable liquid fuel and renewable energy vector. Herein, three distinct routes to make colloidal catalysts based on mixtures of Cu(0) and ZnO nanoparticles (NPs) and using low-temperature organometallic procedures are reported. The colloids are surface coordinated by a phosphinate ligand: dioctylphosphinate ([DOPA]−), which delivers a high solubility in organic solvents. Further, the synthetic routes allow fine control of the ZnO:Cu and ligand loadings. The catalysts are prepared by mixing small NPs (2 nm) of either Cu(0) or air-stable Cu2O NPs with ZnO NPs (3 nm), or by the synthesis of Cu(0) in presence of ZnO NPs (ZnO: 2 nm, Cu: 6 nm). The resulting colloidal catalysts are applied in the liquid phase hydrogenation of CO2 to methanol (210 °C, 50 bar, 3 : 1 molar ratio of CO2 : H2). The catalysts typically exhibit 3 times higher rates when compared to a heterogeneous Cu–ZnO–Al2O3 commercial catalyst (21 vs. 7 mmolMeOH gCuZnO−1 h−1). The characterisation of the post-catalysis colloids show clear Cu/ZnO interfaces (HR-TEM), which are formed under reducing conditions, as well as differences in the Cu(0) NP size (from 3 to 7 nm) and nanoscale restructuring of the catalysts. The combination of characterisation and catalytic results indicate that the activity is mostly dictated by the Cu(0) particle size and ligand loading. Smaller Cu(0) NPs exhibited lower turnover frequency (TOF) values, whereas higher ligand loadings ([DOPA]−:(Cu + Zn) of 0.2–1.1) lead to smaller Cu(0) NPs and reduce the formation of Cu/ZnO interfaces. UV-vis spectroscopy reveals that the Cu(0) NPs are more stable to oxidation under air after catalysis than beforehand, potentially due to migration of ZnO onto the Cu surface whilst under catalytic conditions.

Journal article

De Marco M, Menzel R, Bawaked SM, Mokhtar M, Obaid AY, Basahel SN, Shaffer Met al., 2017, Hybrid Effects in Graphene Oxide/Carbon Nanotube-Supported Layered Double Hydroxides: Enhancing the CO2 Sorption Properties, Carbon, Vol: 123, Pages: 616-627, ISSN: 0008-6223

Graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) have been previously used independently as active supports for layered double hydroxides (LDH), and found to enhance the intrinsic CO2 sorption capacity. However, the long-term stability of the materials subjected to temperature-swing adsorption (TSA) cycles still requires improvement. In this contribution, GO and MWCNT are hybridized to produce mixed substrates with improved surface area, and compatibility for the subsequent deposition of LDH platelets, compared to either phase alone. The incorporation of a robust and thoroughly hybridized carbon network considerably enhances the thermal stability of activated, promoted LDH over twenty cycles of gas adsorption-desorption (96% of retention of the initial sorption capacity at the 20th cycle), dramatically reducing the sintering previously observed when either GO or MWCNT were added separately. Detailed characterization of the morphology of the supported LDH, at several stages of the multicycle adsorption process, shows that the initial morphology of the adsorbents is more strongly retained when supported on the robust hybrid GO/MWCNT network; the CO2 adsorption performance correlates closely with the specific surface area of the adsorbents, with both maximized at small loadings of a 1:1 ratio GO:MWCNT substrate.

Journal article

Clancy AJ, anthony D, Fisher S, Leese H, Roberts C, Shaffer Met 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.

Journal article

Anthony DB, Qian H, Clancy AJ, Bismarck A, Greenhalgh ES, Shaffer MSPet 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.

Journal article

Hu S, Laker ZPL, Leese HS, Rubio N, De Marco M, Au H, Skilbeck MS, Wilson NR, Shaffer MSPet al., 2017, Thermochemical functionalisation of graphenes with minimal framework damage, Chemical Science, Vol: 8, Pages: 6149-6154, ISSN: 2041-6520

Graphene and graphene nanoplatelets can be functionalised via a gas-phase thermochemical method; the approach is versatile, readily scalable, and avoids the introduction of additional defects by exploiting existing sites. Direct TEM imaging confirmed covalent modification of single layer graphene, without damaging the connectivity of the lattice, as supported by Raman spectrometry and AFM nano-indentation measurements of mechanical stiffness. The grafting methodology can also be applied to commercially-available bulk graphene nanoplatelets, as illustrated by the preparation of anionic, cationic, and non-ionic derivatives. Successful bulk functionalisation is evidenced by TGA, Raman, and XPS, as well as in dramatic changes in aqueous dispersability. Thermochemical functionalisation thus provides a facile approach to modify both graphene monolayers, and a wide range of graphene-related nanocarbons, using variants of simple CVD equipment.

Journal article

Hart M, White ER, Chen J, McGilvery CM, Pickard CJ, Michaelides A, Sella A, Shaffer MSP, Salzmann CGet al., 2017, Encapsulation and polymerization of white phosphorus inside single-wall carbon nanotubes, Angewandte Chemie International Edition, Vol: 56, Pages: 8144-8148, ISSN: 1521-3757

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT “nanoreactors”. The energies of the possible chain structures were determined computationally, highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed, which is the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.

Journal article

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