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  • 1
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Langmuir-Blodgett mono- and multilayers of ferric stearate have been formed on oxidized silicon wafers. Thermodesorption of these layers was investigated by conversion electron Mössbauer and photoelectron spectroscopy and some complementary methods. Heating of samples in air up to 523 K leads to a desorption of the fatty acid chains, while the ferric ions are left on the substrate surface. These ions do not cluster laterally like it was found for Cd ions. They form a rather homogeneous, closed oxidic layer. This well defined layer may be used afterwards for further studies of surface reactions as well as interface and intra-layer interactions. The surface iron ions were found to exhibit a reasonably high recoilless fraction. Therefore, Mössbauer spectroscopy allows to follow chemical, structural, and magnetic changes of the iron ions even if the surface is covered by less than one monolayer.
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  • 2
    ISSN: 0392-6737
    Keywords: Thin films, growth, structure, epitaxy, and nonelectronic properties ; Structure and morphology, thickness ; Structure, bonding, stereochemistry, and isomerism of biomolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Two triple-chain phospholipid isomers were investigated at the air-water interface by means of fluorescence microscopy and grazing incidence X-ray diffraction (GID). The two lipids differ only in the position of the branched chain at the glycerol backbone. Fluorescence microscopy shows different domain sharp-edged domains. In the case of dendritic domains the chains are more tilted, the deviation from hexagonal symmetry is more pronounced and hence the lattice anisotropy is larger.
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  • 3
    ISSN: 0392-6737
    Keywords: Superconducting materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si è studiata l'elettrointercalazione dei seguenti ioni metallici idrati in cristalli 2H-TaS2: Na+, K+, Ca2+, Zn2+, Mn2+, La3+, Gd3+, Pr3+. Si trattano studi dilatometriciin situ della reazione e le proprietà superconduttrici di questi composti.
    Abstract: Резюме Иссиедуется злектропрослойка следуюших металлических ионов (Na+, K+, Ca2+, Zn2+, Mn2+, Co3+, Gd3+, Pr3) в монокристаллах 2H-TaS2. Приводятся резулътаты дилатометрических исследований и сверхироводящие свойства зтих соединений.
    Notes: Summary The electrointercalation of the following hydrated metal ions into 2H-TaS2 crystals was investigated: Na+, K+, Ca2+, Zn2+, Mn2+, Co2+, La3+, Gd3+, Pr3+. We report onin situ dilatometric studies of the reaction and on superconducting properties of these compounds.
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  • 4
    ISSN: 1435-1536
    Keywords: Electrostatics ; lipid monolayers ; phase transitions ; domain structure ; fluorescence microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electrostatic interactions in monolayers and vesicles of acidic phospholipids are studied by thermodynamical and optical techniques in conjunction with numerical calculations. A nonmonotonic ionic strength dependence with an extremum at 0.1 M (NaCl) is observed for the phase transition temperature of vesicles as well as for the surface pressure of monolayers at low molecular density. This finding is in accordance with the calculations predicting the dominance of charge screening by monovalent counterions only for concentrations above 0.1 M. For lower salt content, however, its increase causes an elevation of the degree of dissociation and thus also electrostatic repulsion. This leads to a higher surface pressure, a lower transition temperature and a smaller size of solid domains observed in the liquid/solid coexistence range of monolayers. This supports the previously published idea, that finite size and repulsion of the domains arise from a different surface charge density in fluid and solid lipid phases.
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  • 5
    ISSN: 1435-1536
    Keywords: ADSA ; phospholipids ; LB film balance ; monolayer isotherms ; BAM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Axisymmetric Drop Shape Analysis (ADSA) has been used to study the surface pressure/area isotherms of insoluble surfactant monolayers. The continuous measurement of surface tension as a function of surface area by increasing and decreasing the drop volume allows to investigate the phase transitions in monolayers. The isotherms of two phospholipids, dipalmitoyl phosphatidyl choline (DPPC) and dimyristoyl phosphatidyl ethanolamine (DMPE), show good agreement with those measured by using a conventional Langmuir-Blodgett film balance, except in the coexistence region. The observed disagreements are discussed in terms of differences in compression rate, curvature of the surface and effect of impurities. Evidence of possible geometric effects on monolayer domain formation and growth is given on the basis of BAM images. Due to the small total surface area, the ADSA technique provides advantages as regards homogeneity of temperature, surface pressure, surface concentration and the symmetry of area changes.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 278 (2000), S. 104-113 
    ISSN: 1435-1536
    Keywords: Key words Facets ; Domain shape ; Monolayer ; Line tension anisotropy ; Arachidic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The formation of facets in domains of three monolayer systems, differing in molecular structure or headgroup charge, is observed by Brewster-angle microscopy under different experimental conditions. Arachidic acid forms faceted domains on increasing the pH of the subphase from pH 12.0 to 12.3 or by adding traces of cholesterol at pH 12.0. The degree of faceting is gradually varied in a mixture of 1-monopalmitoyl-rac-glycerol and 1-O-hexadecyl-rac-glycerol. The surface potentials of the pure substances were measured in order to determine the electrostatic forces in the mixture. Reversible faceting of domains of heptadecanoic acid methyl ester is observed within 2 °C near 30 °C. Faceting in monolayers is explained on the basis of fundamental forces that govern domain texture and shape, including line tension anisotropy and electrostatic repulsive forces. This explanation also accounts for the formation of dendrites along certain directions at domains of arachidic acid and the methyl ester.
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  • 7
    ISSN: 1435-1536
    Keywords: Phospholipid ; Langmuir monolayers ; surface rheology surface dilational elasticity ; surface shear viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The surface viscoelastic properties of monolayers of two phospholipids DPPC (L-α-dipalmitoylphosphatidylcholine) and DMPE (L-α-dimyristoylphosphatidyl-ethanolamin), at the air-water interface have been investigated. Two techniques were used for the investigation. One involved use of an interfacial shear rheometer (torsion pendulum apparatus ISR1), to provide measurements of the shear viscosity ηs as a function of surface pressure, and the second, a modified LB trough with an oscillating barrier to generate periodie dilation and compression so as to measure the dilational elastic modulusE as a function of surface area. Results indicate a strong dependence of ηs andE upon monolayer phases. This suggests that the viscoelastic relaxation of monolayers can be understood as molecular rearrangements, domain exchange and molecular reorientations between different monolayer states.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4258-4265 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The growth kinetics of two-dimensional crystalline phospholipid domains at the air/water interface is studied following a stepwise increase in density of interfacial molecules. In addition to pressure relaxation the development of domain size and shape and impurity distribution could be followed by fluorescence microscopy. All experimental findings agree, within a factor of 3, with results of simple model calculations. These consider the growth kinetics to be controlled by two-dimensional diffusion of impurities from the solid/lipid boundary (constitutional supercooling) and do not use any freely adjustable, but independently measurable parameters.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2006-2010 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Octadecanol monolayers at the air/water interface are studied by grazing incidence x-ray diffraction. At low lateral pressures one observes the diffraction patterns inherent to the next-nearest neighbor tilt of the molecules. The unit cells are found to be distorted at both low (6 °C) and high (33 °C) temperatures due to tilt of the molecules and ordering of their backbones. Unexpectedly, at an intermediate temperature of 22 °C, the unit cell remains hexagonal in the water plane, despite the tilt of the molecules. This behavior is treated in terms of hydrogen bonding with the water molecules and does not imply the existence of a separate phase. Our diffraction study also does not show any indication of a phase transition S*–L2* corresponding to the singularities in the isotherms within the tilted phase. The tilting phase transitions from untilted phases S and LSII seem to be continuous, since the transition pressures obtained by extrapolation of the tilt angle to zero tilt coincide with the ones determined by Brewster angle microscopy. © 1998 American Institute of Physics.
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  • 10
    ISSN: 0392-6737
    Keywords: Thermodynamics of surfaces and interfaces ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Monolayers of a racemic mixture and of the pure S- and R-enantiomers of 3-hexadecyloxy-propane-1,2-diol have been investigated by fluorescence microscopy and grazing incidence X-ray diffraction. Above the transition pressureΠ c domains with a polygonal shape appear. On compressing the monolayers shape instabilities occur. While the spirals of the S-enantiomer turn clockwise and the spirals of the R-enantiomer turn counterclockwise, the spirals from one domain of the racemate exhibit opposite handedness. This behaviour is explained by a separation of enantiomers on the molecular level. At all pressures investigated the enantiomers exhibit an oblique lattice. The tilt angle of the molecules decreases with increasing pressure.
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