Biomedical subjects

Reinhard Sigel

Publications and source records attributed to Reinhard Sigel.

3 recordsLinked to original sources

PubMed2007

Ion distribution around electrostatically stabilized polystyrene latex particles studied by ellipsometric light scattering.

The ion distribution around electrostatically stabilized polystyrene latex spheres for different ionic strengths is investigated by ellipsometric light scattering. This method is sensitive to the refractive index profile around colloidal particles, which is affected by the local salt content. At an average salt concentration of c* = 10(-4) mol L(-1), the ion concentration at the particle interface increases discontinuously, and a layer of high salt content with 20-30 nm thickness is built up. The observation cannot be explained within the framework of the Poisson-Boltzmann equation; it rather resembles a prewetting transition. Interactions that could possibly lead to a stabilization of the observed layer of high salt content are discussed.

Journal Article↗

PubMed2006

Liquid crystal nanoparticles prepared as miniemulsions.

Liquid crystal nanoparticles using the low molecular weight liquid crystal E7 are prepared by a miniemulsion approach with a droplet size between 180 and 630 nm. The sizes of liquid crystal droplets prepared in this work are one of the smallest sizes ever reported for liquid crystals, and they are considerably dependent on the type and amount of the surfactant used, as well as on the amount of hexadecane. Furthermore, the behavior of a liquid crystal confined to small droplets is investigated. DSC measurements reveal a large shift in the nematic-isotropic phase transition temperature. Further investigations on liquid crystal droplets are carried out using AFM measurements showing that these particles have an order of the liquid crystal molecules within the droplets. Light scattering measurements yield the temperature dependence of the anisotropy and the temporal stability of the droplets. An effect of the director fluctuations within the droplets on dynamic depolarized scattering was found.

Journal Article↗

PubMed2006

Ellipsometric light scattering for the characterization of thin layers on dispersed colloidal particles.

The thin interface layer on colloids in a liquid can be characterized by applying nulling ellipsometry to a scattering experiment. Close to 90 degrees scattering angle the ellipsometric quantities tan(Psi) and Delta of particles smaller than the wavelength behave like at the Brewster angle of reflection ellipsometry. The minimum of tan(Psi) and the slope of Delta depend on thickness and refractive index of the layer, while the location of the minimum is sensitive to the refractive index of the particle. As an example, the swelling of a thermosensitive layer on colloidal particles has been determined from measurements at two wavelengths.

Journal Article↗