Using chitosan as a thickener for electrospinning dilute PVA solutions to improve fibre uniformity

Chitosan was added to PVA aqueous solutions as a thickener to improve the electrospinning process. The presence of a small amount of chitosan considerably improved the uniformity of as-spun nanofibres. This improvement is attributed to its significant effect on the solution viscosity and conductivity, with only a slight impact on the surface tension. The concentration of the PVA required to produce bead-free and uniform nanofibres was reduced with the increase in chitosan concentration. The chitosan thickener suppressed the jet break-up and facilitated the jet stretching so that fine and uniform fibres could be electrospun even from a dilute PVA solution.

Two important exceptions to the relationship between energy density and fat content: food with reduced-fat claims and high-fat vegetable-based dishes

Objective: To test the hypothesis that many foods with reduced-fat (RF) claims are relatively energy-dense and that high-fat (HF) vegetable-based dishes are relatively energy-dilute.

Design: Nutrient data were collected from available foods in Melbourne supermarkets that had an RF claim and a full-fat (FF) equivalent. Nutrient analyses were also conducted on recipes for HF vegetable-based dishes that had more than 30% energy from fat but less than 10% from saturated fat. The dietary intake data (beverages removed) from the 1995 National Nutrition Survey were used for the reference relationships between energy density (ED) and percentage energy as fat and carbohydrate and percentage of water by weight.

Statistics: Linear regression modelled relationships of macronutrients and ED. Paired t-tests compared observed and predicted reductions in the ED of RF foods compared with FF equivalents.

Results: Both FF and RF foods were more energy-dense than the Australian diet and the HF vegetable-based dishes were less energy-dense. The Australian diet showed significant relationships with ED, which were positive for percentage energy as fat and negative for percentage energy as carbohydrate. There were no such relationships for the products with RF claims or for the HF vegetable-based dishes.

Conclusion: While, overall, a reduced-fat diet is relatively energy-dilute and is likely to protect against weight gain, there appear to be two important exceptions. A high intake of products with RF claims could lead to a relatively energy-dense diet and thus promote weight gain. Alternatively, a high intake of vegetable-based foods, even with substantial added fat, could reduce ED and protect against weight gain.

Effects of polymer concentration and cationic surfactant on the morphology of electrospun polyacrylonitrile nanofibres

PAN nanofibres were prepared via an electrospinning process. The effect of polymer concentration on the fibre morphology was studied. At a very dilute solution, no fibres were obtained in the electrospinning process. As the concentration increased, the fibre morphology evolved from a beads-on-string structure to a uniform fibre structure with increasing fibre diameters. However, when the same electrospinning process was conducted with the addition of a cationic surfactant, the formation of disconnected beads was prevented, and the number of beads-on-string structures reduced significantly. In addition, the presence of cationic surfactant reduced the average diameter of the electrospun PAN nanofibres.

NMR and Raman studies of a novel fast-ion-conducting polymer-in-salt electrolyte based on LiCF3SO3 and PAN

We report spectroscopic results from investigations of a novel solid polymeric fast-ion-conductor based on poly(acrylonitrile), (PAN, of repeat unit [CH₂CH(CN)]_n), and the salt LiCF₃SO3 . From NMR studies of the temperature and concentration dependencies of ⁷Li- and ^lH-NMR linewidths, we conclude that significant ionic motion occurs at temperatures close to the glass transition temperature of these polymer-in-salt electrolytes, in accordance with a recent report on the ionic conductivity. In the dilute salt-in-polymer regime, however, ionic motion appears mainly to be confined to local salt-rich domains, as determined from the dramatic composition dependence of the ionic conductivity. FT-Raman spectroscopy is used to directly probe the local chemical anionic environment, as well as the Li⁺–PAN interaction. The characteristic δ_s(CF₃) mode of the CF₃SO₃⁻ anion at _~750–780 cm^−l shows that the ionic substructure is highly complex. Notably, no spectroscopic evidence of free anions is found even at relatively salt-depleted compositions (e.g. N:Li_~60–10:1). A strong Li⁺–PAN interaction is manifested as a pronounced shift of the characteristic polymer C=N stretching mode, found at _~2244 cm^−l in pure PAN, to _~2275 cm^−l for Li⁺-coordinated C=N moieties. Our proton-NMR data suggest that upon complexation of PAN with LiCF3 SO₃, the glass transition occurs at progressively lower temperatures.

Recent insights on the role of cryoprotective agents in vitrification

In recent efforts to produce cryoprotective solutions which cause either complete, or almost complete, vitrification of the cell or tissue material, increasingly complex cocktails of solutes have invariably been used. Why some of these solutes are so much more effective in suppressing ice formation than other, related solutes has never been clear. To begin to compare and contrast the role of the solute in aiding vitrification we have examined the nature of the hydrogen bonding interactions between the solute and water and between the solute molecules themselves, via proton nuclear magnetic resonance experiments. These experiments, carried out on neat samples of the solutions, show marked differences between solutes such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, the family of butanediol isomers, dimethylsulfoxide, and so on, at fixed concentration. The solutions also show marked trends in the NMR chemical shift as a function of concentration in any given solution. Thus it appears that, from the point of view of the physical suppression of ice in aqueous solutions, cryoprotective agents which can act as moderately strong bases are optimum. The mechanism by which the solute promotes glass formation was also investigated in a separate series of NMR experiments using more dilute solutions of the solute in water. These experiments indicate that the role of the solute is twofold in that it must (i) effectively suppress the anomalous structuring which occurs in supercooled water and is responsible for the rapid nucleation of ice and (ii) provide a decrease in molecular mobility at low temperatures such that the nucleation probability is decreased and glass formation occurs at a relatively high temperature. It is argued that both such effects can be brought about by the strong hydrogen bonding interactions between water and solutes such as 2,3-butanediol.

Ion clustering in molecular dynamics simulations of sodium iodide solutions

Model systems of sodium iodide dissolved in dimethyl ether or 1,2-dimethoxyethane (glyme) were studied in order to investigate the structural and dynamic properties of ionic solutions in small and polymeric ethers. Full molecular dynamics simulations were performed at a range of different salt concentrations. An algorithm was designed which assigns ions to clusters and then calculates all the terms which contribute to ionic conductivity. In dilute solutions, free ions are the most common ionic species, followed by ion pairs. As the concentration increases, pairs become the most common species, with significant concentrations of clusters with 3 through 6 ions. Changing the solvent from dimethyl ether to glyme significantly decreases the ion clustering due to the chelate effect in which the two oxygens on a solvent stabilize an associated cation. The conductivity in stable systems is shown to be primarily the result of the movement of free ions and the relative movement of ions within neutral pairs. The Nernst-Einstein relation, commonly used in the discussion of polymer electrolytes, is shown to be inadequate to quantitatively describe conductivity in the model systems.

"Rare Earth" texture development in extruded Mg-based alloys

This data collection addresses the problem of low ductility in magnesium alloys, preventing their wider use. It examines a series of dilute alloys in order to determine the effect of composition on the extrusion behaviour and texture, and on the room temperature tensile ductility.

The "refoldability" of selected proteins in ionic liquids as a stabilization criterion, leading to a conjecture on biogenesis

The folding of proteins is usually studied in dilute aqueous solutions of controlled pH, but it has recently been demonstrated that reversible unfolding can occur in other media. Particular stability is conferred on the protein (folded or unfolded) when the process occurs in ‘protic ionic liquids’ (pILs) of controlled proton activity. This activity (‘effective pH’) is determined by the acid and base components of the pIL and is characterized in the present study by the proton chemical shift of the N–H proton. Here we propose a ‘refoldability’ or ‘refolding index’ (RFI) metric for assessing the stability of folded biomolecules in different solvent media, and demarcate high RFI zones in hydrated pIL media using ribonuclease A and hen egg white lysozyme as examples. Then we show that, unexpectedly, the same high RFIs can be obtained in pIL media that are 90% inorganic in character (simple ammonium salts). This leads us to a conjecture related to the objections that have been raised to ‘primordial soup’ theories for biogenesis, objections that are based on the observation that all the bonds involved in biomacromolecule formation are hydrolyzed in ordinary aqueous solutions unless specifically protected. The ingredients for primitive ionic liquids (NH3, CO, HCN, CO2, and water) were abundant in the early earth atmosphere, and many experiments have shown how amino acids could form from them also. Cyclical concentration in evaporating inland seas could easily produce the type of ambient-temperature, non-hydrolyzing, media that we have demonstrated here may be hospitable to biomolecules, and that may be actually encouraging of biopolymer assembly. Thus a plausible variant of the conventional ‘primordial soup’ model of biogenesis is suggested.

Scandium-doped AlN 1D hexagonal nanoprisms : a class of room-temperature ferromagnetic materials

Pretty vacancy: The formation energy of Al vacancies in aluminum nitride is decreased by doping with nonmagnetic scandium ions. These vacancies are shown to be the cause of the room-temperature ferromagnetism in the resulting 1D hexagonal nanoprisms of AlN:Sc, a result that is confirmed by first-principles calculations. The doping approach provides a new route to dilute magnetic semiconductor materials.

A concert of powers and hybrid regionalism in Asia

With the rise of China the strategic competition between the US and China has gained momentum over the last 10 years and is likely to continue in the near future. To deal with this challenge, Hugh White has proposed a concert of powers in Asia. White’s proposal, however, has not received sufficient attention in Asia and is likely to be a failure if Asia does not take it seriously. This article examines the problematic assumptions of White’s proposal and argues that his proposal needs to incorporate the important role of ASEAN, an existing de facto Asian concert of powers. It shifts the idea of a concert of powers towards a new hybrid regionalism, identifies its key components and discusses how this hybrid regionalism can dilute the strategic conflict between China and the US.

Conversion coatings of Mg-alloy AZ91D using trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl)amide ionic liquid

This work reveals the performance of a trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P6,6,6,14][NTf2]) ionic liquid (IL) conversion coating upon AZ91D. Such conversion coatings represent a novel avenue for chromate replacement. An optimization of coating performance was pursued by careful alloy pretreatment to generate a surface on which the coating performs best, as the AZ91 substrate is distinctly different from pure or dilute Mg alloys. The results reveal that a functional conversion coating can be achieved, retarding anodic dissolution kinetics, causing a significant decrease in corrosion rate. The coating efficacy is closely tied to the pretreatment performed, which dictates both the microstructural and electrochemical heterogeneity of the surface. The resulting coatings were found to contain MgxFx and phosphonium cation related components, the proportions of which were dependent on the pretreatment.

Scalable One-Step Wet-Spinning of Graphene Fibers and Yarns from Liquid Crystalline Dispersions of Graphene Oxide: Towards Multifunctional Textiles

Key points in the formation of liquid crystalline (LC) dispersions of graphene oxide (GO) and their processability via wet-spinning to produce long lengths of micrometer-dimensional fibers and yarns are addressed. Based on rheological and polarized optical microscopy investigations, a rational relation between GO sheet size and polydispersity, concentration, liquid crystallinity, and spinnability is proposed, leading to an understanding of lyotropic LC behavior and fiber spinnability. The knowledge gained from the straightforward formulation of LC GO “inks” in a range of processable concentrations enables the spinning of continuous conducting, strong, and robust fibers at concentrations as low as 0.075 wt%, eliminating the need for relatively concentrated spinning dope dispersions. The dilute LC GO dispersion is proven to be suitable for fiber spinning using a number of coagulation strategies, including non-solvent precipitation, dispersion destabilization, ionic cross-linking, and polyelectrolyte complexation. One-step continuous spinning of graphene fibers and yarns is introduced for the first time by in situ spinning of LC GO in basic coagulation baths (i.e., NaOH or KOH), eliminating the need for post-treatment processes. The thermal conductivity of these graphene fibers is found to be much higher than polycrystalline graphite and other types of 3D carbon based materials.

Solvent extraction and purification of sugars from hemicellulose hydrolysates using boronic acid carriers

Research was performed to determine whether it was technically feasible to use boronic acid extractants to purify and concentrate the sugars present in hemicellulose hydrolysates. Initially, five types of boronic acids (phenylboronic acid, 3,5-dimethylphenylboronic acid, 4-tert-butylphenylboronic acid, trans-β-styreneboronic acid or naphthalene-2-boronic acid) dissolved in an organic diluent (Shellsol® 2046 or Exxal® 10) containing the quaternary amine Aliquat® 336 were tested for their ability to extract sugars (fructose, glucose, sucrose and xylose) from a buffered, immiscible aqueous solution. Naphthalene- 2-boronic acid was found to give the greatest extraction of xylose regardless of which diluent was used. Trials were then conducted to extract xylose and glucose from solutions derived from the dilute acid hydrolysis of sugar cane bagasse and to then strip the loaded organic solutions using an aqueous solution containing hydrochloric acid. This produced a strip solution in which the xylose concentration had been increased over 7× that of the original hydrolysate while reducing the concentration of the undesirable acid-soluble lignin by over 90%. Hence, this process can be exploited to produce high concentration xylose solutions suitable for direct fermentation.