Australian Institute for Innovative Materials - Papers

Optical switching of protein interactions on photosensitive-electroactive polymers measured by atomic force microscopy

Amy Gelmi — Sun, 12 May 2013 21:10:29 PDT

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.

The nanostructure of three-dimensional scaffolds enhances the current density of microbial bioelectrochemical systems

Victoria Flexer — Sun, 21 Apr 2013 23:40:32 PDT

Bioelectrochemical systems encompass a range of electrochemical systems wherein microorganisms are used as biocatalysts. These range from classical microbial fuel cells to novel microbial electrosynthesis processes. The future of practical applications relies on increased performance. In all cases the development of new electrode materials is essential to overcome the low current densities of bioelectrochemical systems. Here we describe a new biocompatible, highly conductive three-dimensional scaffold electrode, NanoWeb-RVC, with a hierarchical porous structure, synthesized by direct growth of carbon nanotubes on a macroporous substrate. The nanostructure of these electrodes enhances the rate of bacterial extracellular electron transfer while the macrostructure ensures efficient mass transfer to and from the electrode surface. NanoWeb-RVC electrodes showed a current density of (6.8 ± 0.3) mA cm-2, almost three times higher than a control electrode with the same macroporous structure but lacking the nanostructure. This current density is among the highest reported to date for a microbial bioanode.

PEGylation of platinum bio-electrodes

Zhilian Yue — Sun, 21 Apr 2013 20:00:18 PDT

Controlling protein interactions at the implanted electrode interface is becoming an important strategy for the management of foreign body responses that have proven to be detrimental to the long-term performance of neural prosthesis. In this study, PEGylation was conducted on platinum bio-electrodes to render the surface protein-resistant. The PEGylated electrode was investigated using a quartz crystal microbalance-dissipation, electrochemical impedance spectroscopy and cyclic voltammetiy.

Passive dorsiflexion stiffness is poorly correlated with passive dorsiflexion range of motion

John W. Whitting — Sun, 21 Apr 2013 20:00:18 PDT

Nonlinear response of topological insulators in the terahertz regime

Qinjun Chen — Sun, 21 Apr 2013 19:55:10 PDT

We report that the surface states of Bi2Se3 exhibit strong nonlinear optical responses in the terahertz regime. The third order nonlinear optical conductance can be observed by applying a moderate electric field. The thermal influence on nonlinear optical responses of the surface states of Bi2Se3 is also studied over different temperature and frequency ranges. 2012 IEEE.

Giant interlayer magnetoresistances and strong anisotropy in p-type Sb2Te3 single crystals

Zengji Yue — Sun, 21 Apr 2013 19:50:11 PDT

Anisotropic interlayer magneto-transport properties have been studied over a broad range of temperatures and magnetic fields in p-type Sb2Te3 single crystals. Giant interlayer magnetoresistance (MR) of up to 400% was observed, which exhibits quadratic field dependences in low fields and becomes linear at high fields without any trend towards saturation. The interlayer MR displays strong anisotropy and is attributable to the anisotropy of the Fermi surface. The observed giant anisotropic interlayer MR could find applications in p-type Sb2Te3 based magneto-electronic devices.

Development of energy-efficient cryogenic leads with high temperature superconducting films on ceramic substrates

A V. Pan — Sun, 21 Apr 2013 19:50:11 PDT

High temperature superconductor (HTS) material can be used for the implementation of high-speed low-heat conduction data links to transport digital data from 4 K superconductor integrated circuits to higher-temperature parts of computing systems. In this work, we present a conceptual design of energy efficient interface and results in fabricating such HTS leads. Initial calculations have shown that the microstrip line cable geometry for typical materials employed in production of HTS thin films can be a two-layered film for which the two layers of about 10 cm long are separated by an insulation layer with as low permittivity as possible. With this architecture in mind, the pulsed laser deposition process has been designed in a 45 cm diameter vacuum chamber to incorporate an oscillating sample holder with homogeneous substrate heating up to 900 degrees C, while the laser plume is fixed. This design has allowed us to produce 200 nm to 500nm thick, 7 cm to 10 cm long YBa2Cu3O7 thin films with the homogeneous critical temperature (T-c) of about 90 K. The critical current density (J(c)) of the short samples obtained from the long sample is of (2 +/- 1) x 10(10) A/m(2). Lines of 3-100 mu m wide have been successfully patterned along the length of the samples in order to directly measure the T-c and J(c) values over the entire length of the samples, as well as to attempt the structuring of multichannel data lead prototype. (C) 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of Guest Editors.

Spinel LiNixMn2-xO4 as cathode material for aqueous rechargeable lithium batteries

F X. Wang — Sun, 21 Apr 2013 19:40:12 PDT

Ni-doped spinel LiNixMn2-xO4 (x = 0, 0.05, 0.10) samples were prepared by a sol-gel method. Structure and morphology of the samples were characterized by X-ray diffraction, scanning electron microscopy, Brunnauer-Emmet-Teller method and inductively coupled plasma atomic absorption spectrometry. The electrochemical behavior as a cathode material (positive mass) for aqueous rechargeable lithium batteries (ARLBs) was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, capacity measurements and cycling tests. The results show that the LiNi 0.1Mn1.9O4 electrode presents the best rate and cycling performance but low reversible capacity. In contrast, the LiNi 0.05Mn1.95O4 electrode shows a higher reversible capacity and relatively good cycling behavior. At a current density of 150 mA g-1, LiNi0.05Mn1.95O4 delivers a reversible capacity of 102 mA h g-1. At the relative high current densities of 1500 and 3000 mA g-1, the LiNi 0.05Mn1.95O4 electrode still delivers reversible capacities of 95.0 and 88.7 mA h g-1, respectively. The Ni-doped samples show excellent cycling life in 0.5 mol L-1 Li 2SO4 aqueous solution. The capacity retention ratios for LiNi0.05Mn1.95O4 and LiNi0.10Mn 1.90O4 after 800 cycles at a current density of 1500 mA g-1 are 79.4% and 91.1%, respectively, much higher than that for the undoped LiMn2O4 at only 37.8%. 2013 Elsevier Ltd. 2013 Elsevier Ltd. All rights reserved.

Effects of the sintering temperature on the flux-pinning mechanism and the activation energy of malic-acid doped MgB2

S R. Ghorbani — Sun, 21 Apr 2013 19:35:15 PDT

The flux-pinning mechanism and activation energy of 10 wt % malic acid-doped MgB2 were investigated by measuring of the critical current density and resistivity as a function of magnetic field and temperature. A crossover field, Bsb, was observed from the single vortex to the small vortex bundle pinning regime. For the sintered sample, the temperature dependence of Bsb(T) at low temperature is in good agreement with the δℓ pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation. The activation energy was decreased by increasing the magnetic field and increased by increasing sintering temperature.

Preparation and characterisation of graphene composite hydrogels

Nicholas J. Whiteside — Sun, 21 Apr 2013 19:30:18 PDT

Stable dispersions containing graphene and gellan gum are used to form composite films. Incorporation of graphene into the gellan gum matrix results in mechanical reinforcement and electrical conductivity at low and high graphene loading fractions, respectively. Graphene-containing gellan gum hydrogel films are prepared by immersion of composite films in Ca2+ cross-linking solutions. The resulting hydrogels are electrically conducting and exhibit reinforcement compared to the corresponding gellan gum hydrogels. 2013 Elsevier B.V.

Reduced graphene oxide with superior cycling stability and rate capability for sodium storage

Yunxiao Wang — Sun, 21 Apr 2013 19:30:17 PDT

Sodium ion battery is a promising electrical energy storage system for sustainable energy storage applications due to the abundance of sodium resources and their low cost. In this communication, the electrochemical properties of sodium ion storage in reduced graphene oxide (RGO) were studied in an electrolyte consisting of 1 M NaClO4 in propylene carbonate (PC). The experimental results show that the RGO anode allowed significant sodium ion insertion, leading to higher capacity at high current density compared to the previously reported results for carbon materials. This is due to the fact that RGO possesses higher electrical conductivity and is a more active host, with large interlayer distances and a disordered structure, enabling it to store a higher amount of Na ions. RGO anode exhibits high capacity combined with long-term cycling stability at high current densities, leading to reversible capacity as high as 174.3 mAh g-1 at 0.2 C (40 mA g-1), and even 93.3 mAh g-1 at 1 C (200 mA g-1) after 250 cycles. Furthermore, RGO could yield a high capacity of 141 mAh g-1 at 0.2 C (40 mA g-1) over 1000 cycles. 2013 Elsevier Ltd. All rights reserved.

Combined effects of hydrogen back-pressure and NbF5 addition on the dehydrogenation and rehydrogenation kinetics of the LiBH4- MgH2 composite system

Jianfeng Mao — Sun, 21 Apr 2013 19:25:10 PDT

It is well known that the dehydrogenation pathway of the LiBH 4-MgH2 composite system is highly reliant on whether decomposition is performed under vacuum or a hydrogen back-pressure. In this work, the effects of hydrogen back-pressure and NbF5 addition on the dehydrogenation kinetics of the LiBH4-MgH2 system are studied under either vacuum or hydrogen back-pressure, as well as the subsequent rehydrogenation and cycling. For the pristine sample, faster desorption kinetics was obtained under vacuum, but the performance is compromised by slow absorption kinetics. In contrast, hydrogen back-pressure remarkably promotes the absorption kinetics and increases the reversible hydrogen storage capacity, but with the penalty of much slower desorption kinetics. These drawbacks were overcome after doping with NbF5, with which the dehydrogenation and rehydrogenation kinetics was significantly improved. In particular, the enhanced kinetics was observed to persist well, even after 9 cycles, in the case of the NbF5 doped sample under hydrogen back-pressure, as well as the suppression of forming Li2B12H12. Furthermore, the mechanism that is behind these effects of NbF5 additive on the reversible dehydrogenation reaction of the LiBH4-MgH2 system is discussed. 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd.

Manganese-based layered coordination polymer: Synthesis, structural characterization, magnetic property, and electrochemical performance in lithium-ion batteries

Qi Liu — Sun, 21 Apr 2013 19:20:12 PDT

Manganese-based layered coordination polymer ([Mn- (tfbdc)(4,4′-bpy)(H2O)2], Mn−LCP) with microporous structure was synthesized by reaction of 2,3,5,6-tetrafluoroterephthalatic acid(H2tfbdc) and 4,4′-bipyridine(4,4′-bpy) with manganese(II) acetate tetrahydrate in water solution. Mn−LCP was characterized by elemental analysis, IR spectra, thermogravimetric analysis, X-ray single-crystal structure analysis, and powder X-ray diffraction. Magnetic susceptibility data from 300 to 1.8K show that there is a weak antiferromagnetic exchange between Mn(II) ions in Mn−LCP. As anode material, the Mn−LCP electrode exhibits an irreversible high capacity in the first discharge process and a reversible lithium storage capacity of up to about 390 mA h/g from the fourth cycle. It might provide a new method for finding new electrode materials in lithium-ion batteries

Hydrolysis and dispersion properties of aqueous Y2Si2O7 suspensions

Ziqi Sun — Sun, 21 Apr 2013 19:05:10 PDT

The dispersion of aqueous c-Y2Si2O7 suspensions, which contain only one component but have a complex ion environment, was studied by the introduction of two different polymer dispersants, polyethylenimine (PEI) and polyacrylic acid (PAA). The suspension without any dispersant remains stable in the pH range of 9-11.5 because of electrostatic repulsion, while it is flocculated upon stirring due to the readsorption of hydrolyzed ions on the colloid surface. However, suspensions with 1 dwb%PEI exhibit greater stability in the pH range of 4-11.5. The addition of PEI shifts the isoelectric point (IEP) of the suspensions from pH 5.8 to 10.8. Near the IEP (pHIEP510.8), the stability of the suspensions with PEI is dominated by the steric effect. When the pH is decreased to acid direction, the stabilization mechanism is changed from steric hindrance to an electrosteric effect little by little. PAA also has the effect of reducing the hydrolysis speed via a ''buffer effect'' in the basic pH range, but the lack of adsorption between the highly ionized anionic polymer molecules and the negative colloid particle surfaces shows no positive effect on hydrolysis of colloids and on the stabilization of Y2Si2O7 suspensions.

The influence of CuFe2o4 nanoparticles on superconductivity of MgB2

Nikolina Novosel — Sun, 21 Apr 2013 18:55:09 PDT

The influence of CuFe2O4 nanoparticle doping on superconducting properties of Fe-sheated MgB2 wires has been studied. The wires containing 0, 3 and 7.5 wt.% of monodisperse superparamagnetic nanoparticles (∼ 7 nm) were sintered at 650◦C or 750◦C for 1 hour in the pure argon atmosphere. X-ray diffraction patterns of doped samples showed very small maxima corresponding to iron boride and an increase in the fraction of MgO phase indicating some interaction of nanoparticles with Mg and B. Both magnetic and transport measurements (performed in the temperature range 2−42 K and magnetic field up to 16 T) showed strong deterioration of the superconducting properties upon doping with CuFe2O4. The transition temperatures, Tc, of doped samples decreased for about 1.4 K per wt.% of CuFe2O4. Also, the irreversibility fields Birr(T) decreased progressively with increasing doping. Accordingly, also the suppression of Jc with magnetic field became stronger. The observed strong deterioration of superconducting properties of MgB2 wires is at variance with reported enhancement of critical currents at higher temperatures (determined from magnetization) in bulk MgB2 samples doped with Fe3O4 nanoparticles. The probable reason for this discrepancy is briefly discussed.

Morphology tunable self-assembled Sr2P2O7:Ce3+, Mn2+ phosphor and luminescence properties

Meng Jiao Xu — Sun, 21 Apr 2013 18:45:13 PDT

Uniform orange-to-red spherical phosphors of Sr2P2O7:Ce3+, Mn2+ have been synthesized by the co-precipitation method and characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. The results indicate that the morphology, size, and photoluminescence properties of Sr2P2O7:Ce3+, Mn2+ phosphors can be effectively controlled by the reaction and the sintering temperatures. Energy transfer from Ce3+ to Mn2+ in Sr2P2O7 phosphor was observed from photoluminescence spectra of Sr2P2O7:Ce3+, Sr2 P2O7:Mn2+, and Sr2P2O7:Ce3+, Mn2+. Moreover, based on a self-assembly process, a possible formation mechanism for the spherical phosphors is proposed. The uniform phosphor spheres obtained in this work exhibit great potential for high-resolution display devices such as light emitting diodes.

Conducting polymer coated neural recording electrodes

Alexander R. Harris — Thu, 18 Apr 2013 19:25:10 PDT

Neural recording electrodes suffer from poor signal to noise ratio, charge density, biostability and biocompatibility. This paper investigates the ability of conducting polymer coated electrodes to record acute neural response in a systematic manner, allowing in depth comparison of electrochemical and electrophysiological response. Approach. Polypyrrole (Ppy) and poly-3,4-ethylenedioxythiophene (PEDOT) doped with sulphate (SO4) or para-toluene sulfonate (pTS) were used to coat iridium neural recording electrodes. Detailed electrochemical and electrophysiological investigations were undertaken to compare the effect of these materials on acute in vivo recording. Main results. A range of charge density and impedance responses were seen with each respectively doped conducting polymer. All coatings produced greater charge density than uncoated electrodes, while PEDOT-pTS, PEDOT-SO 4 and Ppy-SO4 possessed lower impedance values at 1 kHz than uncoated electrodes. Charge density increased with PEDOT-pTS thickness and impedance at 1 kHz was reduced with deposition times up to 45 s. Stable electrochemical response after acute implantation inferred biostability of PEDOT-pTS coated electrodes while other electrode materials had variable impedance and/or charge density after implantation indicative of a protein fouling layer forming on the electrode surface. Recording of neural response to white noise bursts after implantation of conducting polymer-coated electrodes into a rat model inferior colliculus showed a general decrease in background noise and increase in signal to noise ratio and spike count with reduced impedance at 1 kHz, regardless of the specific electrode coating, compared to uncoated electrodes. A 45 s PEDOT-pTS deposition time yielded the highest signal to noise ratio and spike count. Significance. A method for comparing recording electrode materials has been demonstrated with doped conducting polymers. PEDOT-pTS showed remarkable low fouling during acute implantation, inferring good biostability. Electrode impedance at 1 kHz was correlated with background noise and inversely correlated with signal to noise ratio and spike count, regardless of coating. These results collectively confirm a potential for improvement of neural electrode systems by coating with conducting polymers. 2013 IOP Publishing Ltd.

Engineering a multimodal nerve conduit for repair of injured peripheral nerve

A F. Quigley — Thu, 18 Apr 2013 19:20:11 PDT

Injury to nerve tissue in the peripheral nervous system (PNS) results in long-term impairment of limb function, dysaesthesia and pain, often with associated psychological effects. Whilst minor injuries can be left to regenerate without intervention and short gaps up to 2 cm can be sutured, larger or more severe injuries commonly require autogenous nerve grafts harvested from elsewhere in the body (usually sensory nerves). Functional recovery is often suboptimal and associated with loss of sensation from the tissue innervated by the harvested nerve. The challenges that persist with nerve repair have resulted in development of nerve guides or conduits from non-neural biological tissues and various polymers to improve the prognosis for the repair of damaged nerves in the PNS. This study describes the design and fabrication of a multimodal controlled pore size nerve regeneration conduit using polylactic acid (PLA) and (PLA):poly(lactic-co-glycolic) acid (PLGA) fibers within a neurotrophin-enriched alginate hydrogel. The nerve repair conduit design consists of two types of PLGA fibers selected specifically for promotion of axonal outgrowth and Schwann cell growth (75:25 for axons; 85:15 for Schwann cells). These aligned fibers are contained within the lumen of a knitted PLA sheath coated with electrospun PLA nanofibers to control pore size. The PLGA guidance fibers within the nerve repair conduit lumen are supported within an alginate hydrogel impregnated with neurotrophic factors (NT-3 or BDNF with LIF, SMDF and MGF-1) to provide neuroprotection, stimulation of axonal growth and Schwann cell migration. The conduit was used to promote repair of transected sciatic nerve in rats over a period of 4 weeks. Over this period, it was observed that over-grooming and self-mutilation (autotomy) of the limb implanted with the conduit was significantly reduced in rats implanted with the full-configuration conduit compared to rats implanted with conduits containing only an alginate hydrogel. This indicates return of some feeling to the limb via the fully-configured conduit. Immunohistochemical analysis of the implanted conduits removed from the rats after the four-week implantation period confirmed the presence of myelinated axons within the conduit and distal to the site of implantation, further supporting that the conduit promoted nerve repair over this period of time. This study describes the design considerations and fabrication of a novel multicomponent, multimodal bio-engineered synthetic conduit for peripheral nerve repair. 2013 IOP Publishing Ltd.

Lithium rich and deficient effects in LixCoPO4 (x = 0.90, 0.95, 1, 1.05) as cathode material for lithium-ion batteries

Jiantie Xu — Thu, 11 Apr 2013 20:00:20 PDT

A series of LixCoPO4 (x = 0.90, 0.95, 1, 1.05) compounds with different lithium content in the starting compositions were prepared by the sol-gel method. The phase identification was carried out by X-ray diffraction and neutron diffraction. The structure, atom positions, and occupancies were characterized by neutron diffraction. The morphology of LixCoPO4 (x = 0.90, 0.95, 1, 1.05) was examined by field emission scanning electron microscopy. Electrochemical analysis indicated that Li0.95CoPO4 presented the highest discharge capacity at various current densities among all the different x value compounds. The Li0.95CoPO4 showed better cycling stability and coulombic efficiency in the room temperature ionic liquid electrolyte ([C3mpyr][NTf2] containing 1 M LiNTf2) at various current densities in the voltage range of 3.5-5.0 V than in the conventional electrolyte (1 M LiPF6 in ethylene carbonate:diethyl carbonate).

High performance visible light driven photocatalysts silver halides and graphitic carbon nitride (X = Cl, Br, I) nanocomposites

Yonghuan Lan — Thu, 11 Apr 2013 19:50:11 PDT

Novel visible light-driven phtotocatalysts composed by silver halides and graphitic carbon nitride (i.e. AgX@g-C3N4, X = Cl, Br, I) were synthesized by in situ precipitation of AgX nanoparticles on the surface of sheet-like g-C3N4. The resultant AgX@g-C3N4 nanocomposites were characterized with state-of-the-art instruments, showing significant enhancement in photocatalytic degradation of methyl orange under the irradiation of visible light. Their excellent photocatalytic performance is attributed to the efficient separation of photogenerated electron-hole pairs and their higher photostability in comparison with pure AgX. (C) 2012 Elsevier Inc. All rights reserved.