Small-angle X-ray scattering and near-infrared vibrational spectroscopy of water confined in aerosol-OT reverse micelles. 2008

Sangeetha Balakrishnan, and Nadeem Javid, and Hermann Weingärtner, and Roland Winter
Physical Chemistry II, Ruhr-University Bochum,D-44780 Bochum, Germany.

The state of water confined in Aerosol-OT-hydrocarbon-water reverse micelles with cyclohexane, n-pentane, n-octane, and n-dodecane as apolar solvents is investigated by small-angle X-ray scattering and near-infrared vibrational spectroscopy of the first overtone of the OH stretching mode of water. The experiments focus on water/AOT molecular ratios W(0)=2-20, where water is strongly affected by the confinement and surface-water interactions. The pair-distance distribution functions derived from the small-angle scattering patterns allows a detailed characterization of the topology of these systems, and they indicate deviations from monodisperse, spherical water pools for some of these hydrocarbon systems. In contrast to a common assumption, the pool size does not scale linearly with W(0) in going from dry reverse micelles (W(0)-->0) to essentially bulk-like water (W(0)>20). The first overtone of the OH-stretching vibration exhibits highly structured spectra, which reveal significant changes in the hydrogen bonding environment upon confinement. The spectra are rationalized by a core/shell model developed by Fayer and co-workers. This model subdivides water into core water in the interior of the micelle and shell water close to the interface. Core water is modelled by the properties of bulk water, while the properties of shell water are taken to be those of water at W(0)=2. The model allows the representation of the spectra at any hydration level as a linear combination of the spectra of core and shell water. Different approaches are critically reviewed and discussed as well.

UI MeSH Term Description Entries
D008823 Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as EMULSIONS. Micelle
D004143 Dioctyl Sulfosuccinic Acid All-purpose surfactant, wetting agent, and solubilizer used in the drug, cosmetics, and food industries. It has also been used in laxatives and as cerumenolytics. It is usually administered as either the calcium, potassium, or sodium salt. Dioctyl Sulfosuccinates,Docusate,Aerosol OT,Colace,DEH-Na-SS,DOSS,Diethylhexyl Sodium Sulfosuccinate,Dioctyl Sulfosuccinate,Dioctyl Sulfosuccinic Acid, Ammonium Salt,Dioctyl Sulfosuccinic Acid, Barium Salt,Dioctyl Sulfosuccinic Acid, Calcium Salt,Dioctyl Sulfosuccinic Acid, Magnesium Salt,Dioctyl Sulfosuccinic Acid, Potassium Salt,Dioctyl Sulfosuccinic Acid, Sodium Salt,Dioctylsulfosuccinate,Docusate Calcium,Docusate Potassium,Docusate Sodium,Sodium Bis(2-ethylhexyl)sulfosuccinate,Sodium Dioctyl Sulfosuccinate,Sodium Dioctylsulphosuccinate,Sulfosuccinic Acid bis(2-Ethylhexyl) Ester,DEH Na SS,Dioctyl Sulfosuccinate, Sodium,Dioctylsulphosuccinate, Sodium,Sodium Sulfosuccinate, Diethylhexyl,Sulfosuccinate, Diethylhexyl Sodium,Sulfosuccinate, Dioctyl,Sulfosuccinates, Dioctyl
D006860 Hydrogen Bonding A low-energy attractive force between hydrogen and another element. It plays a major role in determining the properties of water, proteins, and other compounds. Hydrogen Bonds,Bond, Hydrogen,Hydrogen Bond
D014867 Water A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Hydrogen Oxide
D014961 X-Ray Diffraction The scattering of x-rays by matter, especially crystals, with accompanying variation in intensity due to interference effects. Analysis of the crystal structure of materials is performed by passing x-rays through them and registering the diffraction image of the rays (CRYSTALLOGRAPHY, X-RAY). (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Xray Diffraction,Diffraction, X-Ray,Diffraction, Xray,Diffractions, X-Ray,Diffractions, Xray,X Ray Diffraction,X-Ray Diffractions,Xray Diffractions
D053838 Scattering, Small Angle Scattering of a beam of electromagnetic or acoustic RADIATION, or particles, at small angles by particles or cavities whose dimensions are many times as large as the wavelength of the radiation or the de Broglie wavelength of the scattered particles. Also know as low angle scattering. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed) Small angle scattering (SAS) techniques, small angle neutron (SANS), X-ray (SAXS), and light (SALS, or just LS) scattering, are used to characterize objects on a nanoscale. Small Angle Scattering,Low Angle Scattering,Scattering, Low Angle,Angle Scattering, Low,Angle Scatterings, Low,Low Angle Scatterings,Scatterings, Low Angle
D019265 Spectroscopy, Near-Infrared A noninvasive technique that uses the differential absorption properties of hemoglobin and myoglobin to evaluate tissue oxygenation and indirectly can measure regional hemodynamics and blood flow. Near-infrared light (NIR) can propagate through tissues and at particular wavelengths is differentially absorbed by oxygenated vs. deoxygenated forms of hemoglobin and myoglobin. Illumination of intact tissue with NIR allows qualitative assessment of changes in the tissue concentration of these molecules. The analysis is also used to determine body composition. NIR Spectroscopy,Spectrometry, Near-Infrared,NIR Spectroscopies,Near-Infrared Spectrometries,Near-Infrared Spectrometry,Near-Infrared Spectroscopies,Near-Infrared Spectroscopy,Spectrometries, Near-Infrared,Spectrometry, Near Infrared,Spectroscopies, NIR,Spectroscopies, Near-Infrared,Spectroscopy, NIR,Spectroscopy, Near Infrared

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