Enhancement of ion dynamics in PMMA-based gels with addition of TiO2 nano-particles

Solvent and ion dynamics in PMMA based gels have been investigated as a function of the loading of nanosized TiO₂ particles. The gels have a molar ratio of 46.5:19:4.5:30 of ethylene carbonate (EC), propylene carbonate (PC), lithium perchlorate and PMMA, respectively. A series of samples with 0, 4, 6 and 8 wt.% TiO₂ filler were investigated. The diffusion coefficients for the lithium ions and for the two solvents (EC and PC) were investigated by pfg-NMR. It was shown that the addition of filler to the gel electrolytes enhances the diffusion of the cations, while the diffusion of the solvents remains constant. Raman measurements show no significant changes in ion–ion interactions with the addition of fillers, while the ionic conductivity is seen to decrease. However, the sample with 8 wt.% TiO₂ had a conductivity close to that of the unfilled sample.

The additive effect of zwitterion and nano-particles on ion dissociation in polyelectrolytes

To realise the battery potential of gel polyelectrolytes greater ion dissociation, ultimately leading to higher conductivities, must be achieved. Higher conductivities will result through increasing the ion-dissociating properties of the gel polyelectrolyte. The poor degree of ion dissociation arises as the active ion tends to remain in close proximity to the backbone charge. Nano-particle inorganic oxides, and zwitterionic compounds have been shown to act as dissociation enhancers in certain polyelectrolyte systems. In an attempt to further increase ion dissociation the addition of both TiO₂ nano-particles and a zwitterionic compound based on 1-butylimidazolium-3-N-(butanesulphonate) were added to the gel polyelectrolyte system poly (Li-2-acrylamido-2-methyl-1-propane sulphonate-co-N,N′-dimethylacrylamide), poly(Li-AMPS-co-DMAA) to determine if a synergistic effect occurs. Two different solvents were used to determine the breadth of applicability of the additive effect. The use of both dissociators resulted in the maximum ionic conductivity being achieved at lower nano-particle concentrations when compared to an identical system without zwitterion.

Gel electrolytes based on lithium modified silica nano-particles

In this work lithium modified silica (Li-SiO₂) nano-particles were synthesized and used as a single ion lithium conductor source in gel electrolytes. It was found that Li-SiO₂ exhibited good compatibility with DMSO, DMA/EC (a mixture of N,N-dimethyl acetamide and ethylene carbonate) and the ionic liquid, N-methyl-N-propyl pyrrolidinium bis(trifluoromethylsulfonyl) amide ([C₃mpyr][NTf₂]). Several gel electrolytes based on Li-SiO₂ were obtained. These gel electrolytes were investigated by DSC, solid state NMR, conductivity measurements and cyclic voltammetry. Conductivities as high as 10⁻³ S/cm at room temperature were observed in these nano-particle gel electrolytes. The results of electrochemical tests showed that some of these materials were promising for using as lithium conductive electrolytes in electrochemical devices, with high lithium cycling efficiency evident.

Dielectrophoretically assembled particles : feasibility for optofluidic systems

This work presents the dielectrophoretic manipulation of sub-micron particles suspended in water and the investigation of their optical responses using a microfluidic system. The particles are made of silica and have different diameters of 600, 450, and 250 nm. Experiments show a very interesting feature of the curved microelectrodes, in which the particles are pushed toward or away from the microchannel centerline depending on their levitation heights, which is further analyzed by numerical simulations. In doing so, applying an AC signal of 12 V_p-p and 5 MHz across the microelectrodes along with a flow rate of 1 μl/min within the microchannel leads to the formation of a tunable band of particles along the centerline. Experiments show that the 250 nm particles guide the longitudinal light along the microchannel due to their small scattering. This arrangement is employed to study the feasibility of developing an optofluidic system, which can be potentially used for the formation of particles-core/liquid-cladding optical waveguides.

Reinforcing silk scaffolds with silk particles

Silk fibroin is a useful protein polymer for biomaterials and tissue engineering. In this work, porogen leached scaffolds prepared from aqueous and HFIP silk solutions were reinforced through the addition of silk particles. This led to about 40 times increase in the specific compressive modulus and the yield strength of HFIP-based scaffolds. This increase in mechanical properties resulted from the high interfacial cohesion between the silk matrix and the reinforcing silk particles, due to partial solubility of the silk particles in HFIP. The porosity of scaffolds was reduced from ≈90% (control) to ≈75% for the HFIP systems containing 200% particle reinforcement, while maintaining pore interconnectivity. The presence of the particles slowed the enzymatic degradation of silk scaffolds.

An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes

Silk is a structural protein fiber that is stable over a wide pH range making it attractive for use in medical and environmental applications. Variation in amino acid composition has the potential for selective binding for ions under varying conditions. Here we report on the metal ion separation potential of Mulberry and Eri silk fibers and powders over a range of pH. Highly sensitive radiotracer probes, ⁶⁴Cu²⁺, ¹⁰⁹Cd²⁺, and ⁵⁷Co²⁺ were used to study the absorption of their respective stable metal ions Cu²⁺, Cd²⁺, and Co²⁺ into and from the silk sorbents. The total amount of each metal ion absorbed and time taken to reach equilibrium occurred in the following order: Cu²⁺ > Cd²⁺ > Co ²⁺. In all cases the silk powders absorbed metal ions faster than their respective silk fibers. Intensive degumming of the fibers and powders significantly reduced the time to absorb respective metal ions and the time to reach equilibrium was reduced from hours to 5-15 min at pH 8. Once bound, 45-100% of the metal ions were released from the sorbents after exposure to pH 3 buffer for 30 min. The transition metal ion loading capacity for the silk sorbents was considerably higher than that found for commercial ion exchange resins (AG MP-50 and AG 50W-X2) under similar conditions. Interestingly, total Cu²⁺ bound was found to be higher than theoretically predicted values based on known specific Cu²⁺ binding sites (AHGGYSGY), suggesting that additional (new) sites for transition metal ion binding sites are present in silk fibers.

Novel dielectrophoretic platforms for manipulation and separation of particles

This research presents the development of a microfluidic system which takes advantage of dielectrophoresis to manipulate particles. The system utilises curved microelectrodes to create strong dielectrophoretic forces within the microchannel, and exploits a novel operating strategy by patterning carbon nanotubes between the microelectrodes to trap low-conductive particles.

Protein fiber particles for biomedical applications

Ultrafine protein particles have been fabricated from natural fibres, such as silk and wool. Our studies suggested that particles could be used for fabricating tough macro-porous composites scaffolds for tissue engineering. They are also efficient for reversible binding of metal ions. We are currently analyzing the sorption properties, biocompatibility and biodegradability of a range of particles to evaluate possibility for biomedical and healthcare applications.

Thermodynamics approach to the hydrogen diffusion and phase transformation in titanium particles

The hydrogen diffusion and phase transformation in a titanium particle were studied based on thermodynamic calculation. The mechanisms of hydrogen diffusion in different phases (alpha-Ti, beta-Ti and TiHx) were analyzed. A mobility database was developed for titanium– hydrogen system based on the experimental works on hydrogen diffusion coefficient reported in literature and the fundamental of diffusion. To implement the calculation, a commercial software package for the simulation of diffusion-controlled phase transformation was used. The hydrogen diffusion process, hydrogen distribution, phase transformation and phase growth rate during hydrogenization of a titanium particle at temperatures of 560 K, 800K and 1000K were discussed. The thermodynamics and kinetics analysis provided quantitative insight into the diffusion process and improved the understanding of diffusion mechanism and phase transformation.

New scalar politics : implications for education policy

This paper argues that globalisation has implications for research and theory in the social sciences, demanding that the social no longer be seen as homologous with nation, but also linked to postnational or global fields. This situation has theoretical and methodological implications for comparative education specifically focused on education policy, which traditionally has taken the nation-state as the unit of analysis, and also worked with 'methodological nationalism'. The paper argues that globalisation has witnessed a rescaling of educational politics and policymaking and relocated some political authority to an emergent global education policy field, with implications for the functioning of national political authority and national education policy fields. This rescaling and this reworking of political authority are illustrated through two cases: the first is concerned with the impact of a globalised policy discourse of the ‘knowledge economy’ proselytised by the OECD and its impact in Australian policy developments; the second is concerned explicitly with the constitution of a global education policy field as a commensurate space of equivalence, as evidenced in the OECD’s PISA and educational indicators work and their increasing global coverage. The paper indicatively utilises Bourdieu’s ‘thinking tools’ to understand the emergent global education policy field and suggest these are very useful for doing comparative education policy analysis.