Browsing by Author "Martin, DJ"

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    Clay particles - potential of positron annihilation lifetime spectroscopy (PALS) for studying interlayer spacing
    (Institute of Physics, 2010-08-01) Fong, N; Guagliardo, P; Williams, J; Musumeci, AW; Martin, DJ; Smith, SV
    Characterisation of clays is generally achieved by traditional methods, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). However, clays are often difficult to characterise due to lack of long-range order, thus these tools are not always reliable. Because interlayer spacing in clays can be adjusted to house molecules, there is growing interest to use these materials for drug delivery. Positron annihilation lifetime spectroscopy (PALS) was examined as an alternative tool to characterise a series of well-known clays. XRD of two layered double hydroxides; MgAl-LDH and MgGd-LDH, natural hectorite, fluoromica and laponite, and their PALS spectra were compared. XRD data was used to calculate the interlayer d- spacing in these materials and results show a decrease in interlayer spacing as the heavy metal ions are substituted for those of large ionic radii. Similar results were obtained for PALS data. This preliminary study suggests PALS has potential as a routine tool for characterising clay particles. Further work will examine the sensitivity and reliability of PALS to percent of metal doping and hydration in clay microstructure. © 2020 IOP Publishing
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    Impact of controlled particle size nanofillers on the mechanical properties of segmented polyurethane nanocomposites
    (Inderscience, 2007-08-06) Finnigan, B; Casey, P; Cookson, DJ; Halley, PJ; Jack, KS; Truss, RW; Martin, DJ
    The impact of average layered silicate particle size on the mechanical properties of thermoplastic polyurethane (TPU) nanocomposites has been investigated. At fixed addition levels (3 wt% organosilicate), an increase in average particle size resulted in an increase in stiffness. Negligible stiffening was observed for the smallest particles (30 nm) due to reduced long-range intercalation and molecular confinement, as well as ineffective stress transfer from matrix to filler. At low strain (<= 100%), an increase in filler particle size was associated with an increase in the rate of stress relaxation, tensile hysteresis, and permanent set. At high strain (1200%), two coexisting relaxation processes were observed. The rate of the slower (long-term) relaxation process, which is believed to primarily involve the hard segment rich structures, decreased on addition of particles with an average diameter of 200 nm or less. At high strain the tensile hysteresis was less sensitive to particle size, however the addition of particles with an average size of 200 nm or more caused a significant increase in permanent set. This was attributed to slippage of temporary bonds at the polymer-filler interface, and to the formation of voids at the sites of unaligned tactoids. Relative to the host TPU, the addition of particles with an average size of 30 nm caused a reduction in permanent set. This is a significant result because the addition of fillers to elastomers has long been associated with an increase in hysteresis and permanent set. At high strain, well dispersed and aligned layered silicates with relatively small interparticle distances and favourable surface interactions are capable of imparting a resistance to molecular slippage throughout the TPU matrix. © 2007, Inderscience Enterprises Ltd.
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    Layered double hydroxide nanoparticles incorporating terbium: applicability as a fluorescent probe and morphology modifier
    (Springer, 2010-01) Musumeci, AW; Xu, ZP; Smith, SV; Minchin, RF; Martin, DJ
    Stable and non-invasive fluorescent probes for nanotoxicological investigations are greatly needed to track the fate of nanoparticles in biological systems. The potential for terbium (Tb) to act as a fluorescent probe and its effect on layered double hydroxide (LDH) nanoparticle morphology are presented in this study. Incorporation of Tb during synthesis offers a simple methodology to easily tailor LDH nanoparticle thickness. A three-fold reduction in the average crystallite thickness (from 13 to 4 nm) has been achieved, whilst preferential lateral growth of LDH nanoparticles in the a-b crystal plane has been observed with increasing Tb loadings. Remarkably, Tb-LDH nanoparticles have emitted green fluorescence with a fluorescence quantum yield of 0.044. © 2010, Springer.
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    Nanocomposite bone cements for orthopaedic applications
    (Elsevier, 2010-06-06) Dunne, N; Ormsby, R; McNally, T; Mitchell, CA; Martin, DJ; Halley, PJ; Nicholson, T; Schiller, T; Gahan, LR; Musumeci, AW; Smith, SV
    Poly methylmethacrylate (PMMA) is the principal component of orthopaedic bone cement. However, it is susceptible to fatigue-related cracking or impact-induced failure. We have previously reported that adding MWCNTs (Multi Walled Carbon Nanotubes)(0.1wt.%) significantly improved the mechanical performance of PMMA-based bone cements and reduced the thermal necrosiscaused by the exothermic curing reaction of the cement [1].However, the effect of MWCNTs of various loading (wt.%) and functionality has yet to be considered. Recently there have been increased efforts to determine the effects of nanosized materials in vivo, with a particular emphasis on tracking their movement. Attachment of radioactive metal ions to MWCNTs via a bi-functional caged ligand would potentially allow for labelling and tracking. The objective of this study was to investigate the effect of MWCNT loading and functionality on mechanical, thermal and rheological properties of PMMA cements. In addition a method for radiolabelling MWCNTs has also been investigated Unfunctionalised, carboxyl (–COOH) functionalised and amine(–NH2) functionalised MWCNTs (Nanocyl S.A., Belgium) at varied wt% loadings (0.1, 0.25, 0.5, and 1.0) were incorporated into ColacrylB866 (Lucite International Ltd., UK) bone cement. Static mechanical properties were measured in accordance with ISO 5833:2002 [2].The plane strain fracture toughness was determined using Chevron-Notch Short Rod method [3]. The fatigue properties of the cements were determined in tension – tension with a lower stress of 0.3 MPa and an upper stress of 22.0 MPa being applied at a frequency of2 Hz [4]. Rheology was used to determine the time at which the onset of cure (tons) occurred and the critical gelation time (gel-time). Radioactive labelling of –COOH functionalised MWCNTs with gamma emitting 57Co (T1/2= 270 days) was completed using a bi-functional cage ligand (MeAMN3S3sar).Incorporating MWCNTs (≤0.25wt%) into cement significantly (p-value<0.001) improved the static and dynamic mechanical properties. However greater loadings of MWCNTs did not provide any further improvements and in some cases resulted in significant(p-value<0.001) reductions in mechanical properties. The extent of this effect was dictated by MWCNT functionality and the wt% used. Improvements were attributed to the MWCNTs arresting crack propagation. The exothermic polymerisation reaction for the PMMA cement was significantly reduced when thermally conductive MWCNTs were added. This was supported by the rheological characterisation as adding MWCNTs significantly altered tons and gel-time. The potential to radioactively label MWCNTs was successfully demonstrated, and further work will be conducted to assess the biological implications by tracking the radiolabelled MWCNTs under in vivo conditions. © 2006 Elsevier Ltd.
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    Organization of mixed dimethyldioctadecylammonium and choline modifiers on the surface of synthetic hectorite
    (Academic Press Inc Elsevier Science, 2013-11-01) Andriani, Y; Jack, KS; Gilbert, EP; Edwards, GA; Schiller, TL; Strounina, E; Osman, AF; Martin, DJ
    Understanding the nature of mixed surfactant self-assembly on the surface of organoclays is an important step toward optimizing their performance in polymer nanocomposites and for other potential applications, where selective surface interactions are crucial. In segmented thermoplastic polyurethane nanocomposite systems, dual-modified organoclays have shown significantly better performance compared to their single-modified counterparts. Until now, we had not fully characterized the physical chemistry of these dual-modified layered silicates, but had hypothesized that the enhanced composite performance arises due to some degree of nanoscale phase separation on the nanofiller surface, which enables enhanced compatibilization and more specific and inclusive interactions with the nanoscale hard and soft domains in these thermoplastic elastomers. This work examines the organization of quaternary alkyl ammonium compounds on the surface of Lucentite SWN using X-ray diffraction (XRD), thermogravimetric analysis (TGA), attenuated total reflectance Fourier-transfer infrared (ATR FT-IR), C-13 cross-polarization (CP)/magic angle spinning (MAS) nuclear magnetic resonance (NMR), and small-angle neutron scattering (SANS). When used in combination with choline, dimethyldioctadecylammonium (DMDO) was observed to self-assemble into discontinuous hydrophobic domains. The inner part of these hydrophobic domains was essentially unaffected by the choline (CC); however, surfactant intermixing was observed either at the periphery or throughout the choline-rich phase surrounding those domains. © 2013, Elsevier Ltd.
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    Synthesis and characterization of dual radiolabeled layered double hydroxide nanoparticles for use in in vitro and in vivo nanotoxicology studies
    (American Chemical Society, 2010-01-21) Musumeci, AW; Schiller, TL; Xu, ZP; Minchin, RF; Martin, DJ; Smith, SV
    Layered double hydroxide (LDH) nanomaterials are currently the focus of intense scientific interest due to their potential application in drug and gene delivery research. However, the emerging field of nanotoxicology requires the development of new and more sensitive methodologies to follow the in vivo delivery kinetics as well as the persistence and bioaccumulation of the LDH carriers subsequent to delivery of the payload to the target area. Radioisotopic labeling offers very high detection sensitivity (<10−14 moles) and straightforward quantitation with respect to other labeling techniques. We have shown that incorporation of naturally occurring Co2+ and Ga3+ cations into the LDH structure has a negligible effect on the physiochemical properties of the pristine nanoparticles. Radiolabeling through dual isomorphous substitution of 57Co2+ and 67Ga3+ into the LDH structure offers the utility to accurately track and also follow the structural dissolution of these nanomaterials over a range of biologically relevant pHs. Radiolabeled-LDH kinetic release profiles in conjunction with transmission electron microscopy and X-ray diffraction studies have revealed that the bulk dissolution of LDH occurs with no preferential leaching of the 57Co2+ or 67Ga3+ metal species from the crystal structure. Furthermore, the present study clearly demonstrates how radiolabeling methodologies described here may be adapted for use in other similar clay systems and allow for the first time noninvasive imaging and monitoring of the fate of nanoparticles. © 2010, American Chemical Society