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Absorbed water, mobility

Detectability may be a significant problem with homologous series of unsaturated compounds, particularly //-alkanes. For these compounds, refractive index detection or evaporative light-scattering, both of which are described elsewhere in the book, may be of use. Indirect photometry is a useful detection scheme for compounds that do not absorb in the UV. Acetone, methylethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, and acetophenone are added to an acetonitrile/water mobile phase, generating a negative vacancy peak when the nonchro-mophoric analyte emerges and a positive peak if the ketone is adsorbed and displaced.70 Dodecyl, tetradecyl, cetyl, and stearyl alcohols also have been derivatized with 2-(4-carboxyphenyl)-5,6-dimethylbenzimidazole and the derivatives separated on Zorbax ODS in a mobile phase of methanol and 2-propanol.71... [Pg.161]

All acidic proton conductors discussed so far in this review have relied on the presence of large amounts of water (A = 10—30) as a mobile phase for the conduction of protons. Current targets for automotive use of hydrogen/air fuel cells are 120 °C and 50% or lower relative humidity. Under these conditions, the conductivity of the membrane decreases due to low water uptake at 50% relative humidity and thus creates large resistive losses in the cell. To meet the needs of advanced fuel cell systems, membranes will have to function without large amounts of absorbed water. Organic—inorganic composites are one preferred approach. ... [Pg.368]

Dimethylformamido. Dimethylformamide (DMF) is a colorless, mobile liquid that is miscible with water. Its slight amine odor results form hydrolysis of the DMF by absorbed water to give dimethylamine and formic acid the purified solvent cannot be stored for more than a day or so at room temperature without some decomposition. DMF, with a dielectric constant of 37, is a good solvent for a wide range of organic compounds and it also will dissolve many... [Pg.333]

Instability attributable to excipient-mediated water distribution in solids and powders has been explained by excipient physical properties. " Crystalline materials will not uptake moisture until the deliquescent point is reached. In contrast, amorphous excipients will absorb water until their glass transition temperatures fall below the ambient temperature when the mobility of the molecules has increased so much that excipient crystallization will occur to expel the absorbed water from the crystal lattice. Before crystal-... [Pg.1653]

Oksanen, C.A. and Zografi, G. Molecular mobility in mixtures of absorbed water and solid poly(vinylpyrrolidone), Pharm. Res., 10, 791, 1993. [Pg.308]

Figure 2. The dipole moment of the absorbed water molecules varies from approximately 1.8 to 0.9 for the polyimides and from 1.1 to 0.7 for the polyamide-imides corresponding to fractional polarizabilities of l.O/i -0.4/x. The low values of p (<0.5p ) as seen in all the amide-imide po ymers and several of the ° polyimides, indicate restricted mobility of the water molecules. In the amide-imide polymers, we believe this is due to increased water-polymer interactions such as hydrogen bonding. Other evidence of hydrogen bonding in polyamide-imides is the water-induced plasticization and Tg lowering frequently observed. Figure 2. The dipole moment of the absorbed water molecules varies from approximately 1.8 to 0.9 for the polyimides and from 1.1 to 0.7 for the polyamide-imides corresponding to fractional polarizabilities of l.O/i -0.4/x. The low values of p (<0.5p ) as seen in all the amide-imide po ymers and several of the ° polyimides, indicate restricted mobility of the water molecules. In the amide-imide polymers, we believe this is due to increased water-polymer interactions such as hydrogen bonding. Other evidence of hydrogen bonding in polyamide-imides is the water-induced plasticization and Tg lowering frequently observed.
A high-performance liquid chromatography (HPLC) procedure was developed to analyze the exudate since the constituents absorbed strongly in the UV. Reverse phase chromatography (y Bondapak C.g column with a 90Z acetonitrile-10% 0.1 N acetic acid-water mobile phase) resulted in the separation of two peaks designated A and B. ... [Pg.174]

Clear colorless, very mobile, flammable liquid pleasant odor burning taste. Absorbs water rapidly from air. dj° 0.789. bp 78.5. mp — 114. l. njj 1,361. Flash pt, closed cup 13 C. Miscible with water and with many organic liquids. Keep tightly closed, cool, and away from Jflamef LDM in young, old rats (g/kg) 10.6, 7.06 orally (Wiberg),... [Pg.594]

The hydration effect on PANl-HCl was investigated by NMR [364-367]. Using H NMR, Nechtschein et al. [364],Travers et al. [367] and Alix el at. [366] found that protons fixed to the polymer backbone frequently (in order of lo s ) exchanged for the mobile protons in the absorbed water. Further, the fixed water molecules are present even in the well-dried samples and become mobile upon hydration. Recently, Travers reported that the hydration enhances the on-chain diffusion rate of the polaron, using and [367]. [Pg.304]

All EP2 samples resist chemical degradation in TA. The more mobile phase, which is found in the layers directly after curing, develops in the bulk EP2 only with aging time. Hence, the steel substrates stimulate the observed phase separation. Water induces a similar effect in HTA. Moreover, in all samples, part of the absorbed water is consumed in a chemical reaction that causes the cleavage of the imino ether-like crossHnks. [Pg.479]

In two-phase systems, however, where surfactant and water can partition between a fluid and a liquid phase, significant pressure effects occur. These effects were studied for AOT in ethane and propane by means of the absorption probe pyridine N-oxide and a fluorescence probe, ANS (8-anilino-l-naphthalenesulfonic acid) [20]. The UV absorbance of pyridine A-oxide is related to the interior polarity of reverse micelles, whereas the fluorescence behavior of ANS is an indicator of the freedom of motion of water molecules within reverse micelle water pools. In contrast to the blue-shift behavior of pyridine N-oxide, the emission maximum of ANS increases ( red shift ) as polarity and water motion around the molecule increase. At low pressures the interior polarity, degree of water motion, and absorbance intensity are all low for AOT reverse micelles in the fluid phase because only small amounts of surfactant and water are in solution. As pressure increases, polarity, intensity, and water motion all increase rapidly as large amounts of surfactant and water partition to the fluid phase. The data indicate that the surfactant partitions ahead of the water thus there is a constant increase in size and fluidity of the reverse micelle water pools up to the one-phase point. An example of such behavior is shown in Fig. 4 for AOT in propane with a total fVo of 40. The change in the ANS emission maximum suggests a continuous increase in water mobility, which is due to increasing fVo in the propane phase, up to the one-phase point at 200 bar. [Pg.285]

The internal resistance of the polymer electrolyte membrane depends on the water content of the membrane. The water ionizes add moieties providing mobile protons, like protons in water [1-3]. Absorbed water also swells the membrane, which may affect the interface between the polymer electrolyte and the electrodes. Nafion, a Teflon/perfluorosulfonic acid copolymer, is the most popular polymer electrolyte because it is chemically robust to oxidation and strongly acidic. The electrodes are commonly Pt nanoparticles supported on a nanoporous carbon support and coated onto a microporous carbon cloth or paper. These structures provide high three-phase interface between the electrolyte/catalyst/reactant gas at both the anode and cathode. [Pg.91]


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See also in sourсe #XX -- [ Pg.141 ]




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