No abstract

Aqueous mixtures of egg-yolk lecithin and the bile salt glycochenodeoxycholic acid sodium salt are studied using small-angle neutron scattering. Upon dilution, the shape and size of the aggregates change dramatically. This is due to very different critical micellar concentrations and spontaneous curvatures of lecithin and bile salt. At high concentrations, cylindrical micelles with a length of a few hundred angstroms are formed. As the samples are diluted, the length of the micelles first decreases and then increases by a factor of 3, their flexibility becomes noticeable, and the micelles can be described as semiflexible cylindrical micelles, also known as wormlike micelles. We have developed a mathematical model for the scattering of the wormlike micelles, which takes into account the intermicellar interaction effects. By the simultaneous fitting of the scattering data from a range of concentrations, the concentration-dependent growth law of the micelles can be parametrized. The obtained growth law of the mixed micelles is compared to the growth laws observed in simple micellar systems.

Crystallite size distributions and particle size distributions were determined by transmissions electron microscopy (TEM), X-ray powder diffraction (XRD), and small-angle X-ray scattering (SAXS) for three commercially available TiO 2 powders (P25, UV100, and TiO2_5 nm) and one SSEC produced powder (SSEC78). The theoretical Guinier model was fitted to the experimental obtained XRD data and compared to analytical expressions. Modeling of the XRD spectra showed a difference between the analytical size dependent expressions and the theoretical Guinier model. Primary particle size distributions were extracted from SAXS measurements by the hard sphere model including an interparticle interference factor. The sizes obtained from SAXS were smaller than the sizes obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy confirmed the primary particle sizes and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially available powders showed different morphologies, but SSEC78, UV100, and TiO2_5 nm all consisted of both primary particles as well as a secondary structure comprised of nanosized primary particles agglomeration into larger clusters. P25 showed the largest primary particle size, but did not show a secondary structure.

Dichte Schale: Aus unterschiedlich temperaturempfindlichen Polymeren ließ sich ein Kern‐Schale‐Mikrogel herstellen, dessen Schale bei mittleren Temperaturen eine höhere Segmentdichte Φ aufweist als der Kern (siehe die radialen Dichteprofile: Kern rot, Schale blau). Genauere Informationen liefert die Kleinwinkel‐Neutronenbeugung. Ein neues Formfaktormodell beschreibt die bei unterschiedlichen Temperaturen erhaltenen experimentellen Streukurven.

The aggregation behavior of zinc-free insulin has been studied by small-angle neutron scattering as a function of pH and ionic strength of the solution. The pair distance distribution functions for the 12 samples have been obtained by indirect Fourier transformation. The results show that the diameter of the aggregates is 40 A at pH 11 and 10 mM NaCl, independent of the protein concentration. The largest diameter of about 120 A is found for pH 8, 100 mM NaCl, and a protein concentration of 10 mg/ml. Estimates of the pair distance distribution functions, free of inter-particle correlation effects, were obtained by an indirect Fourier transformation, omitting the data at small scattering vectors, which are influenced by these effects. By this procedure the weight-averaged molecular mass and the average radius of gyration were determined. These parameters vary from 1.3 times the monomer mass and 14 A, to 6.8 times the monomer mass and 31 A, respectively. The mass distribution between the oligomers was determined by a model based on the crystal structure of zinc-free insulin. The results from this model and the Fourier transformations have been compared to an equilibrium model recently introduced by Kadima et al. (1993). The neutron scattering results agree well with the predictions of this model except that broader mass distributions are suggested by neutron scattering.