Correlation of Structure and Function for CO2 Permeation in Polyphosphazene Membranes

Polyphosphazenes are an intriguing class of polymers because molecular substitutions can be made onto the phosphorus and nitrogen backbone after polymerization. Chemical functionality is supplied through selection of pendant group. In general, regardless of pendant group, polyphosphazenes embody a high degree of thermal and chemical stability, although some pendant groups yield more stable polymers as compared to others. For example, many aryloxyphosphazene formulations are stable at temperatures as high as 300 - 400 degrees Celsius, while many alkoxy-substituted polymers decompose at lower temperatures. It has been thought that permeation of the more condensable gases, such as CO2 and H2S, could be enhanced by selection of pendant groups that exhibit higher affinities for these gases. In this paper, over 20 polyphosphazenes with a wide array of pendant groups will be discussed in terms of their CO2 transport properties. From this work, we have concluded that the chemical characteristics of the pendant group largely do not play a role in CO2 or permanent gas transport. More important are the physical characteristics of the polymer. For example, permeabilities were found to correlate well to the glass transition temperature of the polymer, regardless of the polarity of the pendant group. Thus, segmental chain motion and physical state of the polymer appear to play a more dominant role. This result differs sharply from data taken from liquid transport data that suggests a strong similarity in the solubility properties between the permeant and the polymer is required for higher permeation rates

Advances in Acid Concentration Membrane Technology for the Sulfur-Iodine Thermochemical Cycle

One of the most promising cycles for the thermochemical generation of hydrogen is the Sulfur-Iodine (S-I) process, where aqueous HI is thermochemically decomposed into H2 and I2 at approximately 350 degrees Celsius. Regeneration of HI is accomplished by the Bunsen reaction (reaction of SO2, water, and iodine to generate H2SO4 and HI). Furthermore, SO2 is regenerated from the decomposition of H2SO4 at 850 degrees Celsius yielding the SO2 as well as O2. Thus, the cycle actually consists of two concurrent oxidation-reduction loops. As HI is regenerated, co-produced H2SO4 must be separated so that each may be decomposed. Current flowsheets employ a large amount (~83 mol% of the entire mixture) of elemental I2 to cause the HI and the H2SO4 to separate into two phases. To aid in the isolation of HI, which is directly decomposed into hydrogen, water and iodine must be removed. Separation of iodine is facilitated by removal of water. Sulfuric acid concentration is also required to facilitate feed recycling to the sulfuric acid decomposer. Decomposition of the sulfuric acid is an equilibrium limited process that leaves a substantial portion of the acid requiring recycle. Distillation of water from sulfuric acid involves significant corrosion issues at the liquid-vapor interface. Thus, it is desirable to concentrate the acid without boiling. Recent efforts at the INL have concentrated on applying pervaporation through Nafion-117, Nafion-112, and sulfonated poly(etheretherketone) (S-PEEK) membranes for the removal of water from HI/water and HI/Iodine/water feedstreams. In pervaporation, a feed is circulated at low pressure across the upstream side of the membrane, while a vacuum is applied downstream. Selected permeants sorb into the membrane, transport through it, and are vaporized from the backside. Thus, a concentration gradient is established, which provides the driving force for transport. In this work, membrane separations have been performed at temperatures as high as 134 degrees Celsius. Transmembrane fluxes of water are commercially competitive (~5000 g/m2h) and separation factors have been measured as high as 8000, depending on the membrane and the water content. For the Nafion-117 experiments, the common trade off in membrane performance is observed in that as flux is increased, separation factor decreases. Nafion-112, a thinner membrane, exhibited much higher fluxes than the Nafion-117; however without the expected loss in separation factor indicating that the permeability of iodine and HI through Nafion materials is low. Preliminary data for the sulfuric acid concentration suggests performance similar to the HI experiments. All membranes studied for the HI, HI/iodine and sulfuric acid feeds exhibited no degradation in membrane performance during use

Self-sustainable protonic ceramic electrochemical cells using a triple conducting electrode for hydrogen and power production.

The protonic ceramic electrochemical cell (PCEC) is an emerging and attractive technology that converts energy between power and hydrogen using solid oxide proton conductors at intermediate temperatures. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable electrodes are urgently desired to facilitate water oxidation and oxygen reduction reactions, which are the critical steps for both electrolysis and fuel cell operation, especially at reduced temperatures. In this study, a triple conducting oxide of PrNi0.5Co0.5O3-δ perovskite is developed as an oxygen electrode, presenting superior electrochemical performance at 400~600 °C. More importantly, the self-sustainable and reversible operation is successfully demonstrated by converting the generated hydrogen in electrolysis mode to electricity without any hydrogen addition. The excellent electrocatalytic activity is attributed to the considerable proton conduction, as confirmed by hydrogen permeation experiment, remarkable hydration behavior and computations

Membrane Transport Behavior and the Lability of Chloride on Polyphosphazenes Bearing Bulky Substituents

Polyphosphazenes are an intriguing class of inorganic polymers where much of their functionality is derived from pendant groups attached to phosphorus. The backbone of the polymer consists of alternating phosphorus and nitrogen atoms where the bonding is conventionally drawn as alternating double and single bonds. Orbital nodes are located at each phosphorus atom resulting in electron delocalization between phosphorus atoms, but not through them. Thus, the polymer backbone has a high degree of flexibility where halogens or other leaving groups can be effectively displaced with nucleophiles. In this paper, the first known example of a polyphosphazene with large quantities of non-labile chloride substituents induced by neighboring group steric effects will be discussed. This example is the result of the substitution of poly[bis-chlorophosphazene] with the sodium salt of 3,5-di-tert-butylphenol where only 60% of the chlorines were displaced. This contrasts with the 100% substitution observed with other phenols (phenol, 4-tert-butylphenol, 3-methylphenol, etc.)

Molecular Architecture for Polyphosphazene Electrolytes for Seawater Batteries

In this work, a series of polyphosphazenes were designed to function as water resistant, yet ionically conductive membranes for application to lithium/seawater batteries. In membranes of this nature, various molecular architectures are possible and representatives from each possible type were chosen. These polymers were synthesized and their performance as solid polymer electrolytes was evaluated in terms of both lithium ion conductivity and water permeability. The impact that this molecular architecture has on total performance of the membranes for seawater batteries is discussed. Further implications of this molecular architecture on the mechanisms of lithium ion transport through polyphosphazenes are also discussed

The effects of 12 weeks’ resistance training on psychological parameters and quality of life in adults with Facioscapulohumeral, Becker, and Limb–girdle dystrophies

Purpose Investigate the impact of 12-weeks’ moderate-intensity resistance training on psychological parameters in ambulatory adults with Facioscapulohumeral, Becker, and Limb–girdle muscular dystrophy. Methods Seventeen adults with Facioscapulohumeral (n = 6), Limb–girdle (n = 6; types 2A, 2B, 2L, and 2I), or Becker (n = 5) muscular dystrophy took part. Participants were tested at baseline (PRE), after a 12-week control period (PRE2), and after a 12-week supervised resistance training programme (POST). Training included multi-joint and single-joint resistance exercises. Outcomes from self-report questionnaires were health-related quality of life, depressive symptoms, trait anxiety, self-esteem, and physical self-worth. Results No difference in outcome measures, except depressive symptoms, was found in the control period (PRE to PRE2). Symptoms of depression were reduced by 9% from PRE to PRE2 (p < 0.05) and by a further 19% from PRE2 to POST (p < 0.05). Other changes from PRE2 to POST were that trait anxiety reduced by 10%, self-esteem increased by 10%, physical self-worth increased by 20%, and quality of life improved in 8 domains (p < 0.05). Conclusion These findings demonstrate the positive impact of moderate-intensity resistance training on psychological health and quality of life in adults with Facioscapulohumeral, Becker, and Limb–girdle muscular dystrophies. Implications for rehabilitation Resistance training can have a positive impact on psychological health and quality of life in adults with Facioscapulohumeral, Becker, and Limb–girdle muscular dystrophy. Healthcare professionals should consider including moderate-intensity resistance training within the management and treatment programmes of adults with Facioscapulohumeral, Becker, and Limb–girdle muscular dystrophy

Control of Chemical, Thermal, and Gas Transport Properties in Dense Phosphazene Polymer Membranes.

Polyphosphazenes are hybrid polymers having organic pendant groups attached to an inorganic backbone. Phosphazene polymers can be tailored to specific applications through the attachment of a variety of different pendant groups to the phosphazene backbone. Applications for which these polymers have proven useful include solid polymer electrolytes for batteries and fuel cells, as well as, membranes for gas and liquid separations. In past work, phosphazene polymers have been synthesized using mixtures of pendant groups with differing chemical affinities. Specific ratios of hydrophobic and hydrophilic pendant groups were placed on the phosphazene backbone with a goal of demonstrating control of solubility, and therefore chemical selectivity. In this work, a series of phosphazene homo-polymers were synthesized having varying amounts of hydrophobic and hydrophilic character on each individual pendant group. Polymers were synthesized having a hydrophilic portion next to the polymer backbone and the hydrophobic portion on the terminal end of the pendant group. The effects of these combined hydrophobic/hydrophilic pendant groups on polymer morphology and gas transport properties are presented. The following data will be addressed: thermal characterization, pure gas permeability on seven gases (Ar, H2, O2, N2, CO2, and CH4 ), and ideal selectivity for the gas pairs: O2/N2, H2/CO2, CO2/H2, CO2/CH4 and CO2/N2

Synthesis and Characterization of Polyphosphazene Materials for Advanced Lithium-Water Batteries

Development of long-lived high-energy lithium-water batteries hinges upon developing solid polymer electrolytes (SPEs) with the appropriate properties. These polymer membranes paradoxically must allow lithium atoms to pass from the metallic surface, oxidize to the ionic form, and then pass through the membrane to the water outside. At the same time, the membrane must exclude all water, tramp ions, and deleterious gases such as oxygen and carbon dioxide. SPE membranes are the leading choice for lithium-water batteries however, because current non-membrane approaches being pursued by other research groups suffer from two insurmountable problems - storage and non-productive energy loss via direct lithium/water reaction. In this paper, we present the results of our latest investigations into the transport of water and permanent gasses, such as carbon dioxide, through polyphosphazene SPE materials designed to address the challenges inherent in lithium water batteries

A combined beta-beam and electron capture neutrino experiment

The next generation of long baseline neutrino experiments will aim at determining the value of the unknown mixing angle, theta_{13}, the type of neutrino mass hierarchy and the presence of CP-violation in the lepton sector. Beta-beams and electron capture experiments have been studied as viable candidates for long baseline experiments. They use a very clean electron neutrino beam from the beta-decays or electron capture decays of boosted ions. In the present article we consider an hybrid setup which combines a beta-beam with an electron capture beam by using boosted Ytterbium ions. We study the sensitivity to the CP-violating phase delta and the theta_{13} angle, the CP-discovery potential and the reach to determine the type of neutrino mass hierarchy for this type of long baseline experiment. The analysis is performed for different neutrino beam energies and baselines. Finally, we also discuss how the results would change if a better knowledge of some of the assumed parameters was achieved by the time this experiment could take place.Comment: 35 pp, 11 fig

Extinction filters mediate the global effects of habitat fragmentation on animals

Habitat loss is the primary driver of biodiversity decline worldwide, but the effects of fragmentation (the spatial arrangement of remaining habitat) are debated. We tested the hypothesis that forest fragmentation sensitivity—affected by avoidance of habitat edges—should be driven by historical exposure to, and therefore species’ evolutionary responses to disturbance. Using a database containing 73 datasets collected worldwide (encompassing 4489 animal species), we found that the proportion of fragmentation-sensitive species was nearly three times as high in regions with low rates of historical disturbance compared with regions with high rates of disturbance (i.e., fires, glaciation, hurricanes, and deforestation). These disturbances coincide with a latitudinal gradient in which sensitivity increases sixfold at low versus high latitudes. We conclude that conservation efforts to limit edges created by fragmentation will be most important in the world’s tropical forests