David L. Officer

University of Wollongong, City of Greater Wollongong, New South Wales, Australia

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Publications (152)592.78 Total impact

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    ABSTRACT: Here, we show the formation of a poly(2,6-carbazole) derivative during an electrochemical polymerization process. Comparison of 3,5-bis(9-octyl-9H-carbazol-2-yl)pyridine and 3,5-bis(9-octyl-9H-carbazol-3-yl)pyridine by electrochemical and UV-Vis-NIR spectroelectrochemical measurements and DFT calculation prove the formation of poly(2,6-carbazole) derivative. Both of the compounds form stable and electroactive conjugated polymers.
    Macromolecular Rapid Communications 06/2015; DOI:10.1021/marc201500260 · 4.61 Impact Factor
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    RSC Advances 03/2015; 5(37). DOI:10.1039/C4RA14247K · 3.71 Impact Factor
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    ABSTRACT: The photo-conversion efficiency and stability of back-illuminated dye sensitised solar cells with titanium foil based photoanodes are enhanced by a simple nitric acid treatment through which the foil is passivated. This treatment changes the morphology of the titanium foil and increases its electrochemical double layer capacitance.
    01/2015; 3(7). DOI:10.1039/C4TA05407E
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    ABSTRACT: Graphene-based polymer composites are a very promising class of compounds for tissue engineering scaffolds. However, in general the methods of synthesis are environmentally hazardous and residual toxic materials can affect the biocompatibility significantly. In this paper a simple, scalable, environmentally-friendly, microwave-assisted synthesis is described that results in conducting graphene/polycaprolactone composites that retain the processability and biocompatibility of the pristine polymer without introducing possibly hazardous reducing agents. Composites of polycaprolactone and graphene oxide were synthesised in a single step by the ring-opening polymerisation of ε-caprolactone in the presence of dispersed graphene oxide nanosheets under microwave irradiation. The graphene oxide provides a nucleation centre for the crystallisation of the polymer resulting in polymer-functionalised nanosheets. During polymerisation, the graphene oxide was also reduced to conducting graphene. The resulting graphene/polymer composites were comparable to composites prepared by blending previously highly chemically reduced graphene into polycaprolactone, and they could be easily dispersed in a number of solvents or melt extruded for further processing. These three-dimensional melt extruded materials showed excellent biocompatibility and are promising substrates for tissue engineering scaffolds.
    RSC Advances 01/2015; 5(56). DOI:10.1039/C5RA07210G · 3.71 Impact Factor
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    ABSTRACT: Composites of graphene in a chitosan-lactic acid matrix were prepared to create conductive hydrogels that are processable, exhibit tunable swelling properties and show excellent biocompatibility. The addition of graphene to the polymer matrix also resulted in significant improvements to the mechanical strength of the hydrogels, with the addition of just 3 wt % graphene resulting in tensile strengths increasing by over 200 %. The composites could be easily processed into three-dimensional scaffolds with finely controlled dimensions using additive fabrication techniques and fibroblast cells demonstrate good adhesion and growth on their surfaces. These chitosan-graphene composites show great promise for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.
    11/2014; 3(3). DOI:10.1039/C4TB01636J
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    ABSTRACT: The controlled movement of a chemical container by the light-activated expulsion of a chemical fuel, named here "photo-chemopropulsion", is an exciting new development in the array of mechanisms employed for controlling the movement of microvehicles, herein represented by lipid-based microdroplets. This "chemopropulsion" effect can be switched on and off, and is fully reversible.
    Advanced Materials 11/2014; 26(43). DOI:10.1002/adma.201403007 · 15.41 Impact Factor
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    ABSTRACT: A straightforward, systematic approach to the reduction of graphene oxide (GO) that affords dispersions of chemically converted graphene (CCG) in anhydrous organic solvents with decreasing basal plane defects is reported. The extent of reduction can be controlled and optimized, resulting in highly reduced dispersible chemically converted graphene (hrCCG) having an O1S/C1S ratio of 0.06, which approaches that of graphite. The hrCCG dispersion in anhydrous dimethylformamide (DMF) was stable for several months at a concentration of 0.5–0.6 mg mL−1. This process was found to be easily scalable and could be exploited for the large scale production of hrCCG in DMF and its dispersion in other anhydrous organic solvents. This study demonstrates that the stability of the graphene dispersion is critically dependent on the exfoliation process. The improved elimination of basal defects and the restoration of aromaticity, while maintaining dispersion stability on a large scale in an anhydrous organic solvent, greatly increase the potential of this material for a wide variety of applications.
    Carbon 09/2014; 76:368–377. DOI:10.1016/j.carbon.2014.04.088 · 6.16 Impact Factor
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    ABSTRACT: A novel donor-acceptor poly(terthiophene) derivative bearing a C-60 pendant was electropolymerizated from N-methy1-2-(2-[4,4 ''-didecyloxy-2,2 ';5 ',2 '']terthiophen-3 '-yI-ethenyl)fullero[3,4]pyrrolidine (TTh-C-60) solution. The electroreduction of TTh-C-60 and poly(TTh-C-60) showed the presence of complex peaks related to fulleropyrrolidine reduction. The dual nature of these redox couples may be related to increasing Coulombic repulsion or coupling between C-60 substituents. Electrochemical, X-Ray photoelectron spectroscopy (XPS), Ultra-Violet photoelectron (UPS) and UV-Vis spectroscopy also confirm the nature of poly(TTh-C-60). Electrochemical band gap of poly(TTh-C-60) is 0.63 +/- 0.20 eV in TBAP electrolyte and propylene carbonate (PC) solution. Furthermore, we obtained the value of optical energy band gap (E-opt = 0.59 +/- 0.03 eV), the transport energy band gap (E-g (trans) = 1.17 +/- 0.20 eV) and the exciton binding energy (E-b = 0.58 +/- 0.20 eV) for poly(TTh-C-60). The ionization energy values (IE) were determined using UPS spectroscopy (IE = 4.92 +/- 0.10 eV) and electrochemical investigations of the poly(TTh-C-60) polarized in TBAP/DCM (IE = 5.01 +/- 0.10 eV) and TBAP/PC solution (IE = 4.95 +/- 0.10 eV) demonstrating good coincidence of the value. The electrochemical method revealed, that the location of the Fermi level relative to the valence and conduction bands indicates p-type character of semiconducting poly(TTh-C-60). On the other hand photoemission spectroscopy manifests n-type behavior of examined sample. In turn, the UV-Vis result showed that the charge transfer (CT) between poly(TTh) and C-60 unit can suggest, that these chromophores are not entirely independent.
    Electrochimica Acta 09/2014; 141:51–60. DOI:10.1016/j.electacta.2014.06.100 · 4.09 Impact Factor
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    ABSTRACT: Different nanocarbons, that is, single-wall carbon nanotubes, graphene, single-wall carbon nanohorns (SWCNHs), and their respective oxidized analogs have been used to fabricate novel doped TiO2 electrodes for DSSCs. Our results indicate that all of the nanocarbons significantly enhance the device characteristics when compared to standard TiO2 electrodes. Overall, our most outstanding finding is that SWCNH derivatives are also a plausible material for developing highly-efficient DSSCs.
    Advanced Materials 12/2013; 25(45). DOI:10.1002/adma.201301527 · 15.41 Impact Factor
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    ABSTRACT: Dye sensitized solar cells (DSSCs) employing a dimer porphyrin, which was synthesised with two porphyrin units connected without conjugation, have shown that both porphyrin components can contribute to photocurrent generation, that is, more than 50 % internal quantum efficiency. In addition, the open-circuit voltage (Voc) of the DSSCs was higher than that of DSSCs using monomer porphyrins. In this paper, we first optimized cell structure and fabrication conditions. We obtained more than 80% incident photon to current conversion efficiency from the dimer porphyrin sensitized DSSCs and higher Voc and energy conversion efficiency than monomer porphyrin sensitized solar cells. To examine the origin of the higher Voc, we measured electron lifetime in the DSSCs with various conditions, and found that the dimer system increased the electron lifetime by improving the steric blocking effect of the dye layer, whilst the lack of a conjugated linker prevents an increase in the attractive force between conjugated sensitizers and the acceptor species in the electrolyte. The results support a hypothesis; dispersion force is one of the factors influencing the electron lifetime in DSSCs.
    ACS Applied Materials & Interfaces 11/2013; 5(21). DOI:10.1021/am403022d · 5.90 Impact Factor
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    ABSTRACT: In this work fibres and complex three-dimensional scaffolds of a covalently linked graphene-polycaprolactone composite were successfully extruded and printed using a melt extrusion printing system. Fibres with varying diameters and morphologies, as well as complex scaffolds were fabricated using an additive fabrication approach and were characterized. It was found that the addition of graphene improves the mechanical properties of the fibres by over 50% and in vitro cytotoxicity tests showed good biocompatibility indicating a promising material for tissue engineering applications.
    Materials Science Forum 11/2013; 773-774:496-502. DOI:10.4028/www.scientific.net/MSF.773-774.496
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    ABSTRACT: A series of 2,5-bis(2-thien-2-ylethenyl) thiophene-based oligomers with a para-R-arylethenyl substituent have been subjected to electrochemical (cyclic voltammetry and electronic absorption spectroscopy) and density functional theory characterization. The primary aim of this investigation is to characterize the behavior of these oligomers in the oxidized state. Oligomers without methyl ‘end-caps’ undergo facile σ-dimerization; however there is no evidence for the formation of higher oligomers. The oxidized σ-dimers exist in both cationic and dicationic form. Oligomers with methyl ‘end-caps’ do not show any evidence of σ-dimerization. The inductive capacity of the para-R substituent has a significant bearing on the electronic properties of the oligomer, in particular, oligomers with more electron-withdrawing substituents have charge transfer character associated with the dominant electronic excitations.
    Journal of Molecular Structure 09/2013; 1047:80–86. DOI:10.1016/j.molstruc.2013.04.054 · 1.60 Impact Factor
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    ABSTRACT: The origin of simultaneous improvements in the short-circuit current density (Jsc) and open-circuit voltage (Voc) of porphyrin dye-sensitized TiO2 solar cells following white light illumination was studied by systematic variation of several different device parameters. Reduction of the dye surface loading resulted in greater relative performance enhancements, suggesting open space at the TiO2 surface expedites the process. Variation of the electrolyte composition and subsequent analysis of the conduction band potential shifts suggested that a light-induced replacement of surface-adsorbed lithium (Li+) ions with dimethylpropylimidazolium (DMPIm+) ions was responsible for an increased electron lifetime by decreasing the recombination with the redox mediator. Variation of the solvent viscosity was found to affect the illumination time required to generate increased performance, while similar performance enhancements were not replicated by application of negative bias under dark conditions, indicating the light exposure effect was initiated by formation of dye cation molecules following photoexcitation. The substituents and linker group on the porphyrin chromophore were both varied, with light exposure producing increased electron lifetime and Voc for all dyes; however, increased Jsc values were only measured for dyes containing binding moieties with multiple carboxylic acids. It was proposed that the initial injection limitation and/or fast recombination process in these dyes arises from the presence of lithium at the surface, and the improved injection and/or retardation of fast recombination after light exposure is caused by the Li+ removal by cation exchange under illumination.
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    ABSTRACT: Polythiophenes are attractive candidate polymers for use in synthetic cell scaffolds as they are amenable to modification of functional groups as a means by which to increase biocompatibility. In the current study we analysed the physical properties and response of primary myoblasts to three thiophene poly-mers synthesized from either a basic bithiophene monomer or from one of two different thiophene monomers with alkoxy functional groups. In addition, the effect of the dopants pTS − and ClO 4 − was investigated. In general, it was found that pTS − doped polymers were significantly smoother and tended to be more hydrophilic than their ClO 4 − doped counterparts, demonstrating that the choice of dopant significantly affects the polythiophene physical properties. These properties had a significant effect on the response of primary myoblasts to the polymer surfaces; LDH activity measured from cells harvested at 24 and 48 h post-seeding revealed significant differences between numbers of cells attaching to the different thiophene polymers, whilst all of the polymers equally supported cell doubling over the 48 h period. Differences in morphology were also observed, with reduced cell spreading observed on polymers with alkoxy groups. In addition, significant differences were seen in the polymers' ability to support myo-blast fusion. In general pTS − doped polymers were better able to support fusion than their ClO 4 − doped counterparts. These studies demonstrate that modification of thiophene polymers can be used to promote specific cellular response (e.g. proliferation over differentiation) without the use of biological agents.
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    ABSTRACT: Polythiophenes are attractive candidate polymers for use in synthetic cell scaffolds as they are amenable to modification of functional groups as a means by which to increase biocompatibility. In the current study we analysed the physical properties and response of primary myoblasts to three thiophene poly-mers synthesized from either a basic bithiophene monomer or from one of two different thiophene monomers with alkoxy functional groups. In addition, the effect of the dopants pTS − and ClO 4 − was investigated. In general, it was found that pTS − doped polymers were significantly smoother and tended to be more hydrophilic than their ClO 4 − doped counterparts, demonstrating that the choice of dopant significantly affects the polythiophene physical properties. These properties had a significant effect on the response of primary myoblasts to the polymer surfaces; LDH activity measured from cells harvested at 24 and 48 h post-seeding revealed significant differences between numbers of cells attaching to the different thiophene polymers, whilst all of the polymers equally supported cell doubling over the 48 h period. Differences in morphology were also observed, with reduced cell spreading observed on polymers with alkoxy groups. In addition, significant differences were seen in the polymers' ability to support myo-blast fusion. In general pTS − doped polymers were better able to support fusion than their ClO 4 − doped counterparts. These studies demonstrate that modification of thiophene polymers can be used to promote specific cellular response (e.g. proliferation over differentiation) without the use of biological agents.
    06/2013; 1(9):983. DOI:10.1039/c3bm60059a
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    ABSTRACT: We report the first example of a conducting polymer with a merocyanine incorporated into the polymer backbone by electropolymerisation of a spiropyran moiety covalently linked between two alkoxythiophene units. Utilising the known metal coordination capabilities of merocyanines, introduction of cobalt ions into the electropolymerisation led to an enhancement of the conductivity, morphology and optical properties of the polymer films.
    06/2013; 1(25):3913-3916. DOI:10.1039/C3TC30479E
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    ABSTRACT: The ability to switch the physico-chemical properties of conducting polymers opens up new possibilities for a range of applications. Appropriately functionalised materials can provide routes to multi-modal switching, for example, in response to light and/or electrochemical stimuli. This capability is important in the field of bionics wherein remote and temporal control of the properties of materials is becoming attractive. The ability to actuate a film via photonic stimuli is particularly interesting as it facilitates the modulation of interactions between host binding sites and potential guest molecules. In this work, we studied two different poly-terthiophenes: one was functionalised with a spiropyran photoswitch (pTTh-SP) and the second with a non-photoswitchable methyl acetate moiety (pTTh-MA). These substrates were exposed to several cycles of illumination with light of different wavelengths and the resulting effect studied with UV-vis spectroscopy, contact angle and atomic force microscopy (AFM). The AFM tips were chemically activated with fibronectin (FN) and the adhesion force of the protein to the polymeric surface was measured. The pTTh-MA (no SP incorporated) showed a slightly higher average maximum adhesion (0.96 ± 0.14 nN) than the modified pTTh-SP surface (0.77 ± 0.08 nN), but after exposure of the pTTh-SP polymer to UV, the average maximum adhesion of the pTTh-MC (merocyanine form) was significantly smaller (0.49 ± 0.06 nN) than both the pTTh-MA and pTTh-SP. In addition, the tip-sample separation distances of the adhesive interactions are indicative of the FN interaction occurring over a distance more closely related to the average dimensions of its compact conformation. The results suggest that surface energy and hydrophobic forces are predominant in determining the protein adhesion to the films studied and that this effect can be photonically tuned. By extension, this further implies that it should be possible to obtain a degree of spatial and temporal control of the surface binding behaviour of certain proteins with these functionalised surfaces through photo-activation/deactivation, which, in principle, should facilitate patterned growth behaviour (e.g. using masks or directional illumination) or photocontrol of protein uptake and release.
    03/2013; 1(16):2162-2168. DOI:10.1039/C3TB00463E
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    ABSTRACT: Two synthesis routes to graphene/polycaprolactone composites are introduced and the properties of the resulting composites compared. In the first method, mixtures are produced using solution processing of polycaprolactone and well dispersed, chemically reduced graphene oxide and in the second, an esterification reaction covalently links polycaprolactone chains to free carboxyl groups on the graphene sheets. This is achieved through the use of a stable anhydrous dimethylformamide dispersion of graphene that has been highly chemically reduced resulting in mostly peripheral ester linkages. The resulting covalently linked composites exhibit far better homogeneity and as a result, both Young's modulus and tensile strength more than double and electrical conductivities increase by approximate to 14 orders of magnitude over the pristine polymer at less than 10% graphene content. In vitro cytotoxicity testing of the materials showed good biocompatibility resulting in promising materials for use as conducting substrates for the electrically stimulated growth of cells. (C) 2012 Elsevier Ltd. All rights reserved.
    Carbon 02/2013; 52:296-304. DOI:10.1016/j.carbon.2012.09.031 · 6.16 Impact Factor
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    ABSTRACT: Transition-metal complexes of the types [Re(CO)(3)Cl(NN)], [Re(CO)(3)py(NN)](+), and [Cu(PPh(3))(2)(NN)](+), where NN = 4,4'-bis(5-phenyl-1,3,4-oxadiazol-2-yl)-2,2'-bipyridine (OX) and 4,4'-bis(N,N-diphenyl-4-[ethen-1-yl]-aniline)-2,2'-bipyridine (DPA), have been synthesized and characterized. Crystal structures for [Re(CO)(3)Cl(DPA)] and [Cu(PPh(3))(2)(OX)]BF(4) are presented. The crystal structure of the rhenium complex shows a trans arrangement of the ethylene groups, in agreement with density functional theory calculations. The structure of the copper complex displays the planar aromatic nature of the bpy-oxadiazole ligand. Density functional theory modeling of the complexes was supported by comparison of calculated and experimental normalized Raman spectra; the mean absolute deviations of the complexes were <10 cm(-1). The Franck-Condon state was investigated using UV-vis and resonance Raman spectroscopic as well as density functional theory computational techniques. It was shown that the lowest energy absorption peaks are metal to ligand charge transfer and ligand-centered charge transfer for the oxadiazole- and diphenylaniline-substituted bipyridine ligands, respectively. The lowest energy excited states were characterized using transient emission and absorption spectroscopic techniques in conjunction with density functional theory calculations. These showed that the DPA complexes had ligand-centered nonemissive "dark" states with lifetimes ranging from 300 to 2000 ns.
    Inorganic Chemistry 01/2013; 52(3). DOI:10.1021/ic3018387 · 4.79 Impact Factor
  • Biophysical Journal 01/2013; 104(2):531-. DOI:10.1016/j.bpj.2012.11.2937 · 3.83 Impact Factor

Publication Stats

3k Citations
592.78 Total Impact Points

Institutions

  • 2003–2014
    • University of Wollongong
      • • Intelligent Polymer Research Institute
      • • ARC Centre of Excellence for Electromaterials Science
      City of Greater Wollongong, New South Wales, Australia
  • 2013
    • Rowan University
      Camden, New Jersey, United States
  • 1994–2012
    • Massey University
      • Institute of Fundamental Sciences
      Palmerston North City, Manawatu-Wanganui, New Zealand
  • 2006
    • Adam Mickiewicz University
      • Department of Biochemistry
      Posen, Greater Poland Voivodeship, Poland