Effect Of Water Incorporation Research Articles

Effect of water incorporation on the ionic conduction properties of the solid electrolyte material Rb2Ti2O5.(H2O)x

Previous work has demonstrated the accumulation of negative charges on the anode side of the ion conductor Rb2Ti2O5 when placed under voltage between two metallic electrodes. The nature of these accumulated species and of the conducting ions is investigated by a combination of thermogravimetric analysis (TGA), Xray diffraction, dielectric response measurements, charge distribution, IR absorption spectroscopy and nuclear magnetic resonance (NMR) measurements. TGA shows that the as-grown samples have incorporated a considerable amount of water (up to 0.35 H2O per unit cell) that is eliminated at two different temperature thresholds. However, no significant variation of the lattice parameters is observed by X-Ray diffraction. A strong dependence of the dielectric properties and of the accumulated charge density on the water content is demonstrated. All the results point towards a mechanism of proton and hydroxide conduction associated with a change of valence for titanium.

Comparative evaluation of structured oil systems: Shellac oleogel, HPMC oleogel, and HIPE gel.

In lipid-based food products, fat crystals are used as building blocks for creating a crystalline network that can trap liquid oil into a 3D gel-like structure which in turn is responsible for the desirable mouth feel and texture properties of the food products. However, the recent ban on the use of trans-fat in the US, coupled with the increasing concerns about the negative health effects of saturated fat consumption, has resulted in an increased interest in the area of identifying alternative ways of structuring edible oils using non-fat-based building blocks. In this paper, we give a brief account of three alternative approaches where oil structuring was carried out using wax crystals (shellac), polymer strands (hydrophilic cellulose derivative), and emulsion droplets as structurants. These building blocks resulted in three different types of oleogels that showed distinct rheological properties and temperature functionalities. The three approaches are compared in terms of the preparation process (ease of processing), properties of the formed systems (microstructure, rheological gel strength, temperature response, effect of water incorporation, and thixotropic recovery), functionality, and associated limitations of the structured systems. The comparative evaluation is made such that the new researchers starting their work in the area of oil structuring can use this discussion as a general guideline.Practical applicationsVarious aspects of oil binding for three different building blocks were studied in this work. The practical significance of this study includes (i) information on the preparation process and the concentrations of structuring agents required for efficient gelation and (ii) information on the behavior of oleogels to temperature, applied shear, and presence of water. This information can be very useful for selecting the type of structuring agents keeping the final applications in mind. For detailed information on the actual edible applications (bakery, chocolate, and spreads) which are based on the oleogel systems described in this manuscript, the readers are advised to refer our recent papers published elsewhere. (Food & Function 2014, 5, 645–652 and Food & Function 2014, 5, 2833–2841).

WATER EFFECT ON HIGH-PRESSURE ELASTICITY OF OLIVINE, WADSLEYITE AND RINGWOODITE IN Mg2SiO4 BY FIRST-PRINCIPLES

The hydration effects of water on the high-pressure elastic properties of three Mg 2 SiO 4 polymorphs have been investigated using first-principles simulation density functional theory. The effect of water incorporation was simulated by considering Mg 2 SiO 4 crystals with water contents of 0, 1.65 and 3.3 wt%. With increasing water content, the calculated bulk/shear modulus and sound velocities decrease and their pressure derivatives tend to increase. Thus the hydration effect becomes less obvious at higher pressure. The bulk velocity contrasts from olivine to wadsleyite and from wadsleyite to ringwoodite are found to decrease after water incorporation. Our theoretical results indicate that water content and partition around the phase boundaries have profound impact on the structural and seismic properties of the mantle.

First-principles study of the effect of water on the phase transitions in Mg2SiO4 forsterite

First-principles calculations on the phase transitions in Mg2SiO4 forsterite have been performed using density functional theory and generalized gradient approximation (GGA) implemented in the Vienna Ab-initio Simulation Package code. The effect of water incorporation was simulated by considering Mg2SiO4 crystals of three different structural phases with water contents of 0, 1.65, and 3.3 wt.%. The theoretical K 0 calculated from computed P–V curves reproduces the experimental results well. After an empirical correction to take into account the overestimation of pressure by GGA calculations, the transition pressures in anhydrous Mg2SiO4 crystals are consistent with experimental results. As water content increases, the α–β phase boundary shifts towards lower pressure, while the β–γ phase boundary towards higher pressure. Thus, the existence of water can persistently expand the region of the β phase. Further analyses reveal that the density discontinuities caused by α–β and β–γ phase transitions also vary inversely with water content.

Elastic property of organized lipid assembly — Effect of water incorporation and chain melting

The effect of electric field on the capacitance of lipid–water dispersion properly aligned on polyvinyl alcohol coated glass electrodes, shows a transition pattern where a rapid change in orientation of the organized lipid assembly takes place for an electric field above a threshold value ( V th), similar to that of Freedericksz’s transition as observed in the case of thermotropic liquid crystals. The splay elastic constant, k 11 and the bend elastic constant, k 33 have been calculated from the measured values of capacitance of the cell below and above V th. These values change by several orders of magnitude depending upon the presence of water as well as temperature of chain melting of the lipid moiety.

Infrared Spectroscopy of Bis[(perfluoroalkyl)sulfonyl] Imide Ionomer Membrane Materials

Structural properties of the proton-exchanged forms of bis[(perfluoroalkyl)sulfonyl] imide (PFSI) ionomer materials were investigated. The hydration and dehydration of samples prepared as thin films and freestanding membrane were probed by applying transmission infrared spectroscopy. Spectral bands were assigned and effects of water incorporation into membrane pores and channels were understood by drawing upon results from related measurements performed on the structurally similar, perfluorosulfonic acid ionomer, Nafion. Both PFSI and Nafion membrane materials display a prominent infrared absorbance band near 1060 cm(-1) that arises from a vibrational mode of the ionizable group present on the side chains that extend from the poly(tetrafluoroethylene) backbone on the polymers. The mode can be traced to symmetric stretching of the -SO(3)(-) (sulfonate) group in Nafion and to antisymmetric S-N-S stretching within the sulfonyl imide end group (-SO(2)(N(-))SO(2)CF(3)) in the PFSI materials. For Nafion samples, the position and width of the band near 1060 cm(-1) are strongly sensitive to membrane hydration, whereas the band position and shape change only slightly during hydration and dehydration of PFSI materials. The possibility for greater charge delocalization over the sulfonyl imide moiety and shielding of hydrophilic species by the terminal -CF(3) group are suggested to explain the differences. These effects also likely influence the stretching modes of the side chain C-O-C groups. A pair of bands, sensitive to hydration and traceable to different C-O-C groups in a side chain, is present in the 970-990 cm(-1) region of Nafion. However, the two features are not well resolved and are less sensitive to hydration in spectra of PFSI samples. The most intense ionomer spectral bands arise from modes involving C-F stretching motion and appear between 1150 and 1250 cm(-1). Toward the high energy side of the envelope, there is substantial overlap with features of sulfonate group antisymmetric SO stretching modes in Nafion, but SO stretching modes of the sulfonyl imide moiety are higher in energy and better resolved in spectra of the PFSIs. During water uptake from a dry state into PFSI materials, a progression of features characteristic of solvated H(3)O(+) species appears across the water O-H stretching (2800-3800 cm(-1)) and H-O-H bending (1500-2000 cm(-1)) regions, similar to responses observed for water inside proton-exchanged Nafion.

Effect of water incorporation on the diffusion of sodium in an alkaline-earth boroaluminosilicate glass

Tracer diffusion coefficients of sodium ions diffusing in an alkaline-earth boroaluminosilicate glass (Corning Code 1737 glass) were measured by using Na-22 as a radioactive tracer. It was found that the presence of a significant amount of water vapor in the atmosphere surrounding a diffusion sample during diffusion annealing reduces considerably the mobility of sodium in the near-surface region of the glass. This partial immobilization of Na is attributed to an interaction between water dissolved into the glass and diffusing sodium ions.

Effect of water incorporation on the diffusion of sodium in Type I silica glass

The diffusion of sodium ions in Type I silica glass was studied experimentally by using Na-22 as a radioactive tracer at temperatures between 400°C and 700°C. It was found that the sodium tracer diffusion coefficient in as-received glass was well described by an Arrhenius equation. All residual radioactivity profiles observed after pre-annealing glass samples in common and wet air at temperatures between 900°C and 1100°C and performing diffusion anneals at 650°C cannot be described by a single diffusion coefficient. A strong residual radioactivity decrease occurred near the surface, which was followed by a much smaller decrease in the bulk below. This type of profile was attributed to the generation of a near-surface region with a reduced sodium mobility during the pre-annealing. A mathematical model for the analysis of the observed profiles was developed and used to determine sodium tracer diffusion coefficients in the near-surface region and in the bulk. It was found that the sodium tracer diffusion coefficient in the near-surface region was by about two orders of magnitude smaller than that in the bulk. This immobilization of Na is believed to be due to a water-induced structural relaxation in the near-surface region during pre-annealing.