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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265 results found

Hart M, Chen J, Michaelides A, Sella A, Shaffer MSP, Salzmann CGet al., 2019, One-Dimensional Pnictogen Allotropes inside Single-Wall Carbon Nanotubes, INORGANIC CHEMISTRY, Vol: 58, Pages: 15216-15224, ISSN: 0020-1669

Journal article

Gonzalez Carter D, Goode A, Kiryushko D, Masuda S, Hu S, Lopes Rodrigues R, Dexter D, Shaffer MSP, Porter AEet al., 2019, Quantification of blood-brain barrier transport and neuronal toxicity of unlabelled multiwalled carbon nanotubes as a function of surface charge, Nanoscale, ISSN: 2040-3364

Nanoparticles capable of penetrating the blood-brain barrier (BBB) will greatly advance the delivery of therapies against brain disorders. Carbon nanotubes hold great potential as delivery vehicles due to their high aspect-ratio and cell-penetrating ability. Studies have shown multiwalled carbon nanotubes (MWCNT) cross the BBB, however they have largely relied on labelling methods to track and quantify transport, or on individual electron microscopy images to qualitatively assess transcytosis. Therefore, new direct and quantitative methods, using well-defined and unlabelled MWCNT, are needed to compare BBB translocation of different MWCNT types. Using highly controlled anionic (-), cationic (+) and non-ionic (0) functionalized MWCNT (fMWCNT), we correlate UV-visible spectroscopy with quantitative transmission electron microscopy, quantified from c. 270 endothelial cells, to examine cellular uptake, BBB transport and neurotoxicity of unlabelled fMWCNT. Our results demonstrate that: i) a large fraction of cationic and non-ionic, but not anionic fMWCNT become trapped at the luminal brain endothelial cell membrane; ii) despite high cell association, fMWCNT uptake by brain endothelial cells is low (< 1.5% ID) and does not correlate with BBB translocation, iii) anionic fMWCNT have highest transport levels across an in vitro model of the human BBB compared to non-ionic or cationic nanotubes; and iv) fMWCNT are not toxic to hippocampal neurons at relevant abluminal concentrations; however, fMWCNT charge has an effect on carbon nanotube neurotoxicity at higher fMWCNT concentrations. This quantitative combination of microscopy and spectroscopy, with cellular assays, provides a crucial strategy to predict brain penetration efficiency and neurotoxicity of unlabelled MWCNT and other nanoparticle technologies relevant to human health.

Journal article

Nguyen S, Anthony DB, Qian H, Yue C, Singh A, Bismarck A, Shaffer MSP, Greenhalgh ESet 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.

Journal article

Finley J, Henry J, Shaffer M, Pimenta Set al., The influence of variability and defects on the mechanical performance of tailorable composites, Journal of Composite Materials, ISSN: 0021-9983

Aligned hybrid-fibre discontinuous composites offer the ability to tailor their mechanical response through careful microstructural design. However, with tailorability comes microstructural complexity, which in turn leads to many sources of variability and defects. A virtual testing framework was further extended to investigate the influence of variability and defects on the mechanical performance of various aligned discontinuous composite material systems. This approach identified the most critical sources of variability as (i) fibre strength, (ii) the distance between fibre ends, or (iii) the level of fibre-type intermingling, depending on the material system. Fibre vacancy defects were shown to have the most significant influence on the strength and ductility of aligned discontinuous composites, although this sensitivity can be reduced through hybridisation of the fibre types.

Journal article

Lee C, Greenhalgh E, Shaffer M, Panesar Aet al., Optimized microstructures for multifunctional structural electrolytes, Multifuctional Materials, ISSN: 2399-7532

Multifunctional structural materials offer compelling opportunities to realize highly efficient products. However, the need to fulfil disparate functions generates intrinsically conflicting physical property demands. One attractive strategy is to form a bi-continuous architecture of two disparate phases, each addressing a distinct physical property. For example, structural polymer electrolytes combine rigid and ion-conducting phases to deliver the required mechanical and electrochemical performance. Here, we present a general methodology, based on topology optimization, to identify optimal microstructures for particular design considerations. The numerical predictions have been successfully validated by experiments using 3D printed specimens. These architectures are directly relevant to multifunctional structural composites whilst the methodology can easily be extended to identify optimal microstructural designs for other multifunctional material embodiments.

Journal article

Leo BF, Fearn S, Gonzalez-Carter D, Theodorou I, Ruenraroengsak P, Goode A, Mcphail D, Dexter DT, Shaffer MSP, Chung KF, Porter AE, Ryan MPet al., 2019, Label-free TOF-SIMS imaging of sulfur producing enzymes inside microglia cells following exposure to silver nanowires, Analytical Chemistry, Vol: 91, Pages: 11098-11107, ISSN: 0003-2700

There are no methods sensitive enough to detect enzymes within cells, without the use of analyte labelling. Here we show that it is possible to detect protein ion signals of three different H2S-synthesizing enzymes inside microglia after pre-treatment with silver nanowires (AgNW) using time of flight-secondary ion mass spectrometry (TOF-SIMS). Protein fragment ions, including the fragment of amino acid (C4H8N+ - 70 amu), fragments of the sulfur producing cystathionine-containing enzymes and the Ag+ ion signal could be detected without the use of any labels; the cells were mapped using the C4H8N+ amino acid fragment. Scanning electron microscopy imaging and energy dispersive x-ray chemical analysis showed that the AgNWs were inside the same cells imaged by TOF-SIMS and transformed chemically into crystalline Ag2S within cells in which the sulfur producing proteins were detected. The presence of these sulfur producing cystathionine-containing enzymes within the cells was confirmed by Western Blots and confocal microscopy images of fluorescently labelled antibodies against the sulfur producing enzymes. Label-free ToF-SIMS is very promising for the label-free identification of H2S-contributing enzymes and their cellular localization in biological systems. The technique could in future be used to identify which of these enzymes are most contributory.

Journal article

Basma N, Cullen PL, Clancy AJ, Shaffer MSP, Skipper NT, Headen TF, Howard CAet al., 2019, The liquid structure of the solvents dimethylformamide (DMF) and dimethylacetamide (DMA), MOLECULAR PHYSICS, ISSN: 0026-8976

Journal article

Kennedy OW, White R, Shaffer MSP, Warburton PAet al., 2019, Vapour-liquid-solid growth of ZnO-ZnMgO core-shell nanowires by gold-catalysed molecular beam epitaxy, Nanotechnology, Vol: 30, ISSN: 0957-4484

Nanowire heterostructures, combining multiple phases within a single nanowire, modify functional properties and offer a platform for novel device development. Here, ZnO/ZnMgO core–shell nanowires are grown by molecular beam epitaxy. At growth temperatures above 750 °C, Mg diffuses into ZnO making heterostructure growth impossible; at lower shell-growth temperatures (500 °C), the core–shell structure is retained. Even very thin ZnMgO shells show increased intensity photoluminescence (PL) across the ZnO band-gap and a suppression in defect-related PL intensity, relative to plain ZnO nanowires. EDX measurements on shell thickness show a correlation between shell thickness and core diameter which is explained by a simple growth model.

Journal article

Lee W, Clancy A, Fernández-Toribio JC, Anthony D, White E, Solano E, Leese HS, Vilatela JJ, Shaffer MSPet al., 2019, Interfacially-grafted single wall carbon nanotube / poly (vinyl alcohol) composite fibers, Carbon, Vol: 146, Pages: 162-171, ISSN: 0008-6223

Nanocomposites are critically influenced by interfacial interactions between the reinforcement and matrix. Polyvinyl alcohol (PVOH) of varying molecular weights were prepared and grafted to single-walled carbon nanotubes (SWCNTs), to improve the interfacial interaction with a homopolymer PVOH matrix. Nanocomposite fibers were coagulation spun across a broad range of loading fractions, controlled by the spinning dope composition. An intermediate grafted-PVOH molecular weight (10 kDa) maximized grafting ratio, and the final composite mechanical performance; the positive effects were attributed to the increased degree of dispersion of the SWCNTs in the dope, as well as the favorable interface. The PVOH grafting increased the stability of the SWCNT loading fractions (up to 45 wt.%), offering increased strength (up to 1100 MPa) and stiffness (up to 38.5 GPa); at the same time, strain to-failures remained high (up to 23.3%), resulting in high toughness (up to 125 J g-1).

Journal article

Clancy A, Sirisinudomkit P, Anthony D, Thong A, Greenfield J, Salaken Singh MK, Shaffer Met 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.

Journal article

Kennedy OW, White ER, Howkins A, Williams CK, Boyd IW, Warburton PA, Shaffer MSPet al., 2019, Mapping the origins of luminescence in ZnO nanowires by STEM-CL, Journal of Physical Chemistry Letters, Vol: 10, Pages: 386-392, ISSN: 1948-7185

In semiconductor nanowires, understanding both the sources of luminescence (excitonic recombination, defects, etc.) and the distribution of luminescent centers (be they uniformly distributed, or concentrated at structural defects or at the surface) is important for synthesis and applications. We develop scanning transmission electron microscopy-cathodoluminescence (STEM-CL) measurements, allowing the structure and cathodoluminescence (CL) of single ZnO nanowires to be mapped at high resolution. Using a CL pixel resolution of 10 nm, variations of the CL spectra within such nanowires in the direction perpendicular to the nanowire growth axis are identified for the first time. By comparing the local CL spectra with the bulk photoluminescence spectra, the CL spectral features are assigned to internal and surface defect structures. Hyperspectral CL maps are deconvolved to enable characteristic spectral features to be spatially correlated with structural features within single nanowires. We have used these maps to show that the spatial distribution of these defects correlates well with regions that show an increased rate of nonradiative transitions.

Journal article

Liu B, Liu C, De Luca H, Raman Pillai SK, Anthony DB, Li J, Bismarck A, Shaffer M, Chan-Park MBet 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

Journal article

Stanier D, Radhakrishnan A, Gent I, Roy SS, Hamerton I, Potluri P, Scarpa F, Shaffer M, Ivanov DSet al., 2019, Matrix-graded and fibre-steered composites to tackle stress concentrations, COMPOSITE STRUCTURES, Vol: 207, Pages: 72-80, ISSN: 0263-8223

Journal article

Zainol Abidin MS, Herceg T, Greenhalgh ES, Shaffer M, Bismarck Aet al., 2019, Enhanced fracture toughness of hierarchical carbon nanotube reinforced carbon fibre epoxy composites with engineered matrix microstructure, Composites Science and Technology, Vol: 170, Pages: 85-92, ISSN: 0266-3538

Journal article

Clancy AJ, Leese HS, Rubio Carrero N, Buckley DJ, Greenfield JL, Shaffer MSPet al., 2018, Depleting depletion: maintaining single-walled carbon nanotube dispersions after graft-to polymer functionalization, Langmuir, Vol: 34, Pages: 15396-15402, ISSN: 0743-7463

Grafting polymers onto single-walled carbon nanotubes (SWCNTs) usefully alters properties but does not typically yield stable, solvated species directly. Despite the expectation of steric stabilization, a damaging (re)dispersion step is usually necessary. Here, poly(vinyl acetate)s (PVAc) of varying molecular weights are grafted to individualized, reduced SWCNTs at different concentrations to examine the extent of reaction and degree of solvation. The use of higher polymer concentrations leads to an increase in grafting ratio (weight fraction of grafted polymer relative to the SWCNT framework), approaching the limit of random sequentially adsorbed Flory ‘mushrooms’ on the surface. However, at higher polymer concentrations, a larger percentage of SWCNTs precipitate during the reaction; an effect which is more significant for larger weight polymers. The precipitation is attributed to depletion interactions generated by ungrafted homopolymer overcoming Coulombic repulsion of adjacent like-charged SWCNTs; a simple model is proposed. Larger polymers and greater degrees of functionalization favor stable solvation, but larger and more concentrated homopolymers increase depletion aggregation. By using low concentrations (25 μM) of larger molecular weight PVAc (10 kDa), up to 65% of grafted SWCNTs were retained in solution (at 65 μg mL-1) directly after the reaction.

Journal article

Brandley E, Greenhalgh E, Shaffer M, Li Qet al., 2018, Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs, Carbon, Vol: 137, Pages: 78-87, ISSN: 0008-6223

A novel method of applying a two-dimensional Fourier transform (2D-FFT) to SEM wasdeveloped to map the CNT orientation in pre-formed arrays. Local 2D-FFTs were integratedazimuthally to determine an orientation distribution function and the associated Hermanparameter. This approach provides data rapidly and over a wide range of lengthscales.Although likely to be applicable to a wide range of anisotropic nanoscale structures, themethod was specifically developed to study CNT veils, a system in which orientationcritically controls mechanical properties. Using this system as a model, key parameters forthe 2D-FFT analysis were optimised, including magnification and domain size; a model setof CNT veils were pre-strained to 5%, 10% and 15%, to vary the alignment degree. Thealgorithm confirmed a narrower orientation distribution function and increasing Hermanparameter, with increasing pre-strain.To validate the algorithm, the local orientation was compared to that derived from a commonpolarised Raman spectroscopy. Orientation maps of the Herman parameter, derived by bothmethods, showed good agreement. Quantitatively, the mean Herman parameter calculatedusing the polarised Raman spectroscopy was 0.42±0.004 compared to 0.32±0.002 for the 2DFFTmethod, with a correlation coefficient of 0.73. Possible reasons for the modest andsystematic discrepancy were discussed.

Journal article

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, Vol: 130, Pages: 11823-11827, ISSN: 0044-8249

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

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

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