A 13C NMR study of the role of plasticizers in the conduction mechanism of solid polymer electrolytes

The addition of low molecular weight solvents such as dimethyl formamide (DMF) and propylene carbonate (PC) to urethane crosslinked polyethers results in enhancement of polymer segmental motion, as determined in this work from polymer ¹³C spin lattice relaxation measurements (T₁) and glass transition temperatures. The formation of salt-polyether complexes results in a decrease in T₁, even in the presence of the plasticizer, indicating that the polymer ether molecules are still involved in the alkali metal coordination. In a polymer electrolyte containing 1 mol kg⁻¹ LiClO₄ the addition of DMF and PC have significantly different affects on the polymer mobility, although they both enhance the conductivity. The conductivity enhancement therefore is not solely the result of an increased solvent mobility.

Ftir study of ion-pairing effects in plasticized polymer electrolytes

The effect of plasticizer on the ubiquitous ion-pairing observed in polymer electrolytes has been investigated using FTIR as a probe of the local environment of the triflate ion in sodium and lithium triflate based electrolytes. Plasticizers having a range of properties, such as, propylene carbonate, and dimethyl formamide (DMF), have been investigated in the pure state for comparison with the polymer (a random copolymer of ethylene oxide at propylene oxide (mol ratio 3: 1)). The different plasticizers exhibited strikingly different effects on the triflate ion bands normally observed in polyether salt systems. In particular, the cation associated triflate ion bands at 1288 and 1248 cm⁻¹ and the band at 1272 cm⁻¹ which has variously been assigned to the free ion and also to the strongly aggregated anion, are different. PC produces a rapid disappearance of the “free” ion band in favour of the monodentate ion pair. On the other hand, DMF strongly enhances the band near 1270 cm⁻¹ at salt concentrations higher than 0.7 mol kg⁻¹. These observations are discussed in terms of recent ab initio calculations of the triflate vibrational bands.

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.

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.

Poly methacrylate-plasticiser-salt blends as solid polymer electrolytes

Methoxy-ethylene glycol methacrylates, CH₂=CMeCOO(CH₂CH₂O)_nMe (n = 1, 2, 3), ethoxy-triethylene glycol methacrylate, CH₂=CMeCOO(CH₂CH₂O)₃Et, and N,N-dimethylaminoethyl methacrylate, CH₂=CMeCOOCH₂CH₂NMe₂, were used to synthesise the corresponding polymers. Conductivities of these polymers complexed with lithium perchlorate were investigated. Tetraethylene glycol dimethyl ether was used as plasticiser to increase the conductivity of the materials. A conductivity of 10⁻⁵ S cm⁻¹ was obtained at room temperature for the plasticised polymer samples. Effects of polymer structure, plasticiser, salt concentration and temperature on conductivity and glass transition temperature of the polymer electrolytes are discussed.

Mechanical properties of polyether-plasticiser-salt systems as polymer electrolytes

The mechanical properties of urethane crosslinked poly(ethylene oxide-co-propylene oxide) glyceryl ether-plasticiser (tetraethylene glycol dimethyl ether, or methylformamide)-salt (LiClO₄)-based polymer electrolytes have been studied. It was found that, with increasing concentration of salt, the elastic modulus and tensile strength of the materials unexpectedly decrease. This is interpreted in terms of a predominance of intramolecular coordination of the Li⁺ ions by the polymer.

Polymer-in-ionic-liquid electrolytes

In order to achieve high conductivity in a polymer electrolyte, polymer-in-ionic-liquid electrolytes have been explored. It is found in this study that poly[vinylpyrrolidone-co-(vinyl acetate)] (P(VP-c-VA)) in 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide (EtMeIm+Tf2N−) and poly(N,N-dimethyl acrylamide) (PDMAA) in trimethyl butyl ammonium bis(trifluoromethane sulfonyl) amide (N1114+Tf2N−) produce ion-conducting liquids and gels. The P(VP-c-VA)/ EtMeIm+Tf2N− mixture has a conductivity around 10−3 S · cm−1 at 22 °C, for copolymer concentrations up to 30 wt.-%. Thermal analysis shows that the Tg of the P(VP-c-VA)/ EtMeIm+Tf2N− system is well described by the Fox equation as a function of polymer content. Poly(methyl methacrylate) (PMMA)/ EtMeIm+Tf2N− gel electrolytes were prepared by in-situ polymerisation of the monomer in the ionic liquid. In the presence of 0.5–2.0 wt.-% of a crosslinking agent, these PMMA-based electrolytes displayed elastomeric properties and high conductivity (ca. 10−3 S · cm−1) at room temperature.

Transparent uv-shielding films from organic small molecule-intercalated layered double hydroxide nanoplatelets/polymer composite

In this study, layered double hydroxide (LDH) with nitrate as the interlayer anion has been partially exfoliated in dimethyl sulfoxide (DMSO). Atomic force microscopy (AFM) images showed that both the lateral size and the thickness of the LDH nanoplatelets were decreased after DMSO treatment. Formation of transparent LDH suspension in DMSO was observed. Taking this advantage, we have prepared transparent LDH/ethylene-vinyl alcohol copolymer (EVOH) nanocomposite films using DMSO as the processing solvent. Organic small molecules, UV absorbers, were intercalated into the LDH interlayers to incorporate the UV-shielding property into the transparent composite films. The thermal stability of UV absorbers was considerably improved after intercalation, which was attributed to the electrostatic interaction between the guest UV absorbers and the host LDH layers. The prepared composite films were flexible and exhibited excellent UV-shielding capability, but had transmittance as high as 90% in the visible region. The effect of LDH filler on thermal and mechanical properties of the composite films was also examined.

Partial exfoliation of layered double hydroxides in DMSO : a route to transparent polymer nanocomposites

Layered double hydroxides (LDHs), either having nitrate counter anions or intercalated with organic molecules, have been for the first time partially exfoliated in dimethyl sulfoxide (DMSO) to form a transparent suspension. Atomic force microscopy (AFM) images showed that both the lateral size and the thickness of the LDH nanoplatelets were decreased after the exfoliation. The organic-LDHs maintained their intercalation characteristics, i.e. the thermal stability improvement of the incorporated organic anions, after the exfoliation in DMSO. Transparent ethylene-vinyl alcohol copolymer (EVOH) nanocomposite films containing partially exfoliated LDHs intercalated with UV absorbers were prepared using DMSO as the processing solvent. As the first reported example of a highly transparent LDH/polymer composite, the obtained composite film had a visible light transmittance of 90% (comparable to that of the pure matrix), was flexible and exhibited an excellent UV-shielding capability and thermal stability.

Synthesis and characterization of silver nanoparticles and titanium oxide nanofibers : toward multifibrous nanocomposites

A new method was investigated to produce new multiscale fibrous nanocomposites comprised of titanium oxide (TiO₂) nanofibers and silver (Ag) nanoparticles (NPs). The process involved electrospinning TiO₂ precursor solution containing colloidal solution of Ag NPs, and organic solvent (dimethyl-n′n-formamide) to fabricate a porous, nonwoven, free-standing nanofiber mesh. Postprocess heating of the electrospun nanofibers entailed calcination in air environment at 500°C for 3 h. Microemulsion processing was used to generate NPs of Ag in a monodispersed distribution throughout the colloidal solution. X-ray diffraction data were consistent with the anatase phase of TiO2, while transmission electron microscopy and hydrogen desorption measurements revealed a very porous microstructure. It was demonstrated that NP colloidal stability is solvent dependent. It is anticipated that incorporation of metal particles in nanofibers will lead to enhanced photocurrent generation, when used in functional devices.

Synthesis, characterization, and multilayer assembly of pH sensitive graphene−polymer nanocomposites

pH sensitive graphene−polymer composites have been prepared by the modification of graphene basal planes with pyrene-terminated poly(2-N,N′-(dimethyl amino ethyl acrylate) (PDMAEA) and poly(acrylic acid) (PAA) via π−π stacking. The pyrene-terminal PDMAEA and PAA were synthesized using reversible addition−fragmentation chain transfer (RAFT) polymerization with a pyrene-functional RAFT agent. The graphene−polymer composites were found to demonstrate phase transfer behavior between aqueous and organic media at different pH values. Atomic force microscopy (AFM) analysis revealed that the thicknesses of the graphene−polymer sheets were approximately 3.0 nm when prepared using PDMAEA (M_n: 6800 and PDI: 1.12). The surface coverage of polymer chains on the graphene basal plane was calculated to be 5.3 × 10⁻¹¹ mol cm⁻² for PDMAEA and 1.3 × 10⁻¹⁰ mol cm⁻² for PAA. The graphene−polymer composites were successfully characterized using X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR) spectroscopy, and thermogravimetric analysis (TGA). Self-assembly of the two oppositely charged graphene−polymer composites afforded layer-by-layer (LbL) structures as evidenced by high-resolution scanning electron microscopy (SEM) and quartz crystal microbalance (QCM) measurements.

Reactive block copolymer modified thermosets : highly ordered nanostructures and improved properties

A highly ordered poly(dimethyl siloxane)-poly(glycidyl methacrylate) (PDMS-PGMA) reactive diblock copolymer was synthesized and used to modify bisphenol A-type epoxy resin (ER). The PDMS-PGMA block copolymer consisted of epoxy-miscible PGMA blocks and an epoxy-immiscible PDMS block. The PGMA reactive block of the block copolymer formed covalent bonds with cured epoxy and was involved in the network formation, and the PDMS block phase separated to give different ordered and disordered nanostructures at different blend compositions. The solvent cast PDMS-PGMA diblock copolymer showed ordered hexagonal cylindrical morphology. A highly ordered morphology consisting of hexagonal cylinders inside the lamellar morphology was observed in the cured PDMS-PGMA block copolymer. In the cured ER/PDMS-PGMA blends, a variety of morphologies including lamellar, cubic and worm-like and spherical nanostructures were detected depending on the blend composition. Moreover, the addition of this reactive diblock copolymer significantly increases the hydrophobicity and the glass transition temperature. It also improves the tensile strength and tensile ductility of the nanostructured thermosets at low diblock copolymer contents.

The origin of the antibacterial property of bamboo

Bamboo is an eco-friendly and multifunctional plant. Bamboo clothing has recently entered the textile market with a claim for its antimicrobial properties, but without scientific evidence. In this study, the antibacterial activity of plant extracts from Australian-grown bamboo (Phyllostachys pubescens) is investigated. Bamboo extracts were made using water, dimethyl sulphoxide (DMSO) and dioxane and their antibacterial properties were compared against Gram-negative bacteria, Escherichia coli. It was found that the extract made in 20% DMSO aqueous solution showed weak antibacterial activity, whereas the extract made using 90% dioxane aqueous solution exhibited strong antibacterial activity, even after 20 times dilution. The results indicate that antibacterial agents of P. pubescens are located in lignin, not in hemicellulose or other water-soluble chemical components.

Oxygen consumption and blood flow distribution in perfused skeletal muscle of chinook salmon

An isolated, perfused salmon tail preparation showed oxyconformance at low oxygen delivery rates. Addition of pig red blood cells to the perfusing solution at a haematocrit of 5 or 10% allowed the tail tissues to oxyregulate. Below ca. 60 ml O₂ kg⁻¹ h⁻¹ of oxygen delivery (DO₂), VO₂ was delivery dependent. Above this value additional oxygen delivery did not increase VO₂ of resting muscle above ca. 35 ml O₂ kg⁻¹ h⁻¹. Following electrical stimulation, VO₂ increased to ca. 65 ml O₂ kg⁻¹ h⁻¹, with a critical DO₂ of ca. 150 ml O₂ kg⁻¹ h⁻¹. Dorsal aortic pressure fell to 69% of the pre-stimulation value after 5 min of stimulation and to 54% after 10 min. Microspheres were used to determine blood flow distribution (BFD) to red (RM) and white muscle (WM) within the perfused myotome. Mass specific BFD ratio at rest was found to be 4.03 ± 0.49 (RM:WM). After 5 min of electrical stimulation the ratio did not change. Perfusion with saline containing the tetrazolium salt 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) revealed significantly more mitochondrial activity in RM. Formazan production from MTT was directly proportional to time of perfusion in both red and WM. The mitochondrial activity ratio (RM:WM) did not change over 90 min of perfusion.

Adverse effects of cigarette smoke on NO bioavailability : role of arginine metabolism and oxidative stress

Endothelial dysfunction is a hallmark of cardiovascular disease, and the l-arginine:NO pathway plays a critical role in determining endothelial function. Recent studies suggest that smoking, a well-recognized risk factor for vascular disease, may interfere with l-arginine and NO metabolism; however, this remains poorly characterized. Accordingly, we performed a series of complementary in vivo and in vitro studies to elucidate the mechanism by which cigarette smoke adversely affects endothelial function. In current smokers, plasma levels of asymmetrical dimethyl-arginine (ADMA) were 80% higher (P=0.01) than nonsmokers, whereas citrulline (17%; P<0.05) and N-hydroxy-l-arginine (34%; P<0.05) were significantly lower. Exposure to 10% cigarette smoke extract (CSE) significantly affected endothelial arginine metabolism with reductions in the intracellular content of citrulline (81%), N-hydroxy-l-arginine (57%), and arginine (23%), while increasing ADMA (129%). CSE significantly inhibited (38%) arginine uptake in conjunction with a 34% reduction in expression of the arginine transporter, CAT1. In conjunction with these studies, CSE significantly reduced the activity of eNOS and NO production by endothelial cells, while stimulating the production of reactive oxygen species. In conclusion, cigarette smoke adversely affects the endothelial l-arginine NO synthase pathway, resulting in reducing NO production and elevated oxidative stress. In conjunction, exposure to cigarette smoke increases ADMA concentration, the latter being a risk factor for cardiovascular disease.