David L. Officer

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

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Publications (160)552.78 Total impact

  • [Show abstract] [Hide abstract]
    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.
    J. Mater. Chem. B. 11/2014;
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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 09/2014; · 14.83 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. · 6.16 Impact Factor
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    Electrochimica Acta 09/2014; 141:51–60. · 4.09 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; · 5.90 Impact Factor
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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. · 1.40 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 08/2013; · 14.83 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.
    Biomaterials Science. 06/2013; 1:983.
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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.
    J. Mater. Chem. C. 06/2013; 1(25):3913-3916.
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    ABSTRACT: Vapour phase polymerisation (vpp) of PEDOT to incorporate high levels of a sulphonated manganese porphyrin yields a vivid green conducting polymer that, under illumination, catalyzes selective oxidation of water from seawater from ca. 0.40 V (vs. NHE; Pt counter electrode) without observable chlorine formation. This onset potential is comparable to that of certain metal oxide semiconductors that achieve higher photocurrents but are not capable of selectively oxidising the water in seawater.
    Chemical Science 05/2013; 4:2797. · 8.31 Impact Factor
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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.
    J. Mater. Chem. B. 03/2013; 1(16):2162-2168.
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    ABSTRACT: A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2 suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical performance of TiO2 electrodes, cast as single layers, was dependent on the thermal treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent of residual organics and found that acetates from the TiO2 precursor preparation were retained within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness 4 lm produced an energy conversion efficiency as high as 5.4% using this simple thermal treatment.
    Journal of Materials Research 02/2013; 28(3):488-496. · 1.82 Impact Factor
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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. · 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; · 4.59 Impact Factor
  • Biophysical Journal 01/2013; 104(2):531-. · 3.67 Impact Factor
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    ABSTRACT: Four novel nanographene/porphyrin hybrids were prepd., characterized, and probed in solar energy conversion schemes. Exfoliation of graphite by means of immobilizing four different porphyrins onto the basal plane of graphene is accompanied by distinct electronic interactions in both the ground and the excited states. In the ground state, a strong loss in oscillator strength goes hand-in-hand with a notable broadening of the porphyrin transitions and, as such, attests to the shift of electron d. from the electron donating porphyrins to nanographene. In the excited state, a nearly quant. quenching of the porphyrin fluorescence is indicative of full charge transfer. The latter is corroborated by femtosecond transient absorption measurements, which reveal the generation of the one-electron oxidized radical cation of the porphyrins with absorption maxima at 490 and 625 nm in the visible region and conduction band electrons in nanographene with features at 890 and 1025 nm in the near IR region. We have demonstrated the applicability of the new nanographene/porphyrin hybrids in, for example, solar cells. In this regard, the presence of flakes is crucial in terms of influencing the injection processes, preventing aggregation, and reducing recombination losses, which are commonly encountered in porphyrin-based DSSCs.
    Chemical Science 01/2013; 4(8):3085-3098. · 8.31 Impact Factor
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    ABSTRACT: The electropolymerization of pyrrole (Py), 3-(4-tert-butylphenyl)thiophene (TPT) monomer or the mixed Py and TPT monomers on stainless steel mesh substrate were performed in 1 M LiClO4/acetonitrile solution. A much lower potential of 0.75 V was required for the co-electropolymerization of Py and TPT, in sharp contrast to that of 1.20 V for poly(3-(4-tert-butylphenyl)thiophene) (PTPT) formation. The resultant homopolymers and copolymer were characterized with FESEM and FTIR, and assembled into supercapacitors to investigate their electrochemical performances. The copolymer electrode delivered the highest specific capacitance of 291 F g−1 at a scan rate of 5 mV s−1, in comparison with that of 216 and 26 F g−1 for PPy and PTPT, respectively. This copolymer also exhibited a greatly improved cycling stability – only 9% of capacitance decrease was observed after 1000 charging–discharging cycles at a current density of 5 A g−1, while the capacitance losses for PPy and PTPT were 16% and 60%, respectively.
    Synthetic Metals 12/2012; 162(24):2216–2221. · 2.11 Impact Factor
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    ABSTRACT: A novel approach to induce disassembly of electroactive multilayer films fabricated by the layer by layer assembly technique is reported. Electroactive multilayer films are constructed using water soluble polythiophenes, i.e., negatively charged poly[ammonium (3-thienyl)ethoxypropanesulfonate] (SPT) and positively charged poly[3-(3′-thienyloxy)ethyltriethylammonium] (APT). “Induced” dissolution of the films in response to applied potential is investigated using a quartz crystal microbalance equipped with an electrochemical cell module (EC-QCM-D). Disassembly of the films is observed in response to three different potentials: +650, –650, and ±650 mV; however the time for dissolution varies as a function of the potential with films subject to +650 mV dissolving fully in 19 h compared to 42 h for films subject to –650 mV. These electroactive films and their controlled dissolution under applied potential represent an attractive architectural feature for bionic devices that could benefit from their conductivity and dissolution over time.
    Advanced Functional Materials 12/2012; 22(23). · 10.44 Impact Factor

Publication Stats

864 Citations
552.78 Total Impact Points

Institutions

  • 2006–2014
    • University of Wollongong
      • • ARC Centre of Excellence for Electromaterials Science
      • • Intelligent Polymer Research Institute
      City of Greater Wollongong, New South Wales, Australia
  • 2013
    • Shinshu University
      • Division of Chemistry and Materials
      Shonai, Nagano, Japan
  • 2012–2013
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      Erlangen, Bavaria, Germany
    • Dublin City University
      Dublin, Leinster, Ireland
  • 2006–2013
    • University of Otago
      • Department of Chemistry
      Dunedin, Otago, New Zealand
  • 2010
    • Monash University (Australia)
      • School of Chemistry, Clayton
      Melbourne, Victoria, Australia
  • 1994–2010
    • Massey University
      • Institute of Fundamental Sciences
      Palmerston North City, Manawatu-Wanganui, New Zealand
  • 2009
    • University of Malaga
      • Department of Physical Chemistry
      Málaga, Andalusia, Spain