Reinhard Sigel

Glycopolymer vesicles with an asymmetric membrane

Direct dissolution of glycosylated polybutadiene-poly(ethylene oxide) block copolymers can lead to the spontaneous formation of vesicles or membranes, which on the outside are coated with glucose and on the inside with poly(ethylene oxide).

Effects of sample polydispersity and beam profile on ellipsometric light scattering

Ellipsometric light scattering (ELS) is shown to selectively extract the coherent scattering contribution representing the averaged properties of a particle ensemble. This property is essential for the previously reported [Erbe et al., Phys. Rev. E73, 031406 (2006)] high sensitivity of ELS to the refractive index profile at particle interfaces. Two mechanisms for coherence loss in ELS measurements are discussed: sample polydispersity and illumination by a Gaussian beam. Suitable experimental quantities for a distinction of coherent and incoherent scattering contributions are introduced. Furthermore, the application of the concepts to reflection ellipsometry at rough surfaces is discussed.

Separation of coherent and incoherent scattering contributions in ellipsometric light scattering experiments on latex mixtures

Mixtures of poly(styrene) latices were used to vary the sample polydispersity for an investigation of polydispersity effects on ellipsometric light scattering (ELS) data. A procedure for high-accuracy ELS measurements is presented and the experimental distinction of coherent and incoherent scattering contributions is demonstrated. The ellipsometric parameters tan (phiQ) and delta are solely determined from coherent scattering and represent averaged ensemble properties, independent of the width of the size distribution. The change in polydispersity shows up in the parameter tan(phiI), which is affected by incoherent contributions. The average particle size detected by ELS can be estimated from the intensity-weighted size distribution. A radial local birefringence in the particles has been detected and attributed to stress birefringence due to the action of the interface tension on the particles during their growth.

Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).

Activation and fluoride-assisted phosphating of aluminum-silicon-coated steel.

Phosphating is a crucial process in the corrosion protection of metals. Here, activation and fluoride-assisted tricationic phosphating is investigated on aluminum-silicon (AS) coated steel surfaces. Dynamic light scattering results from the activation bath show a bimodal size distribution, with hydrodynamic radii of ~400 nm and ~10 μm. For the smaller particle fraction, static light scattering results are consistent with the interpretation of disklike particles as scattering objects. Particles of the larger fraction sediment with time. In the presence of electrolyte, the scattering intensity from the larger particle fraction increases. Coagulation with time is suggested to be related to the decrease in activity of the activation bath. Scanning Auger microscopy (SAM) shows a higher phosphorus concentration after titanium phosphate activation in the Al-rich areas compared to the Si-rich areas of the AS coatings. There is no correlation between the size of the species in the activation bath, and the size of the phosphate-containing regions on the activated surface. Phosphating was performed in the presence of hexafluorosilicic acid, H2SiF6, ammonium hydrogen difluoride, NH4HF2, and both, at an initial pH of 2.5. The absence of crystals after phosphating with H2SiF6 is an indication that SiF6(2-) is the final product of the oxide dissolution in the presence of fluoride. In the presence of NH4HF2, the Si-rich regions of the surface are phosphated before the Si-poor (Al-rich) regions. Hence, the phosphate distribution after activation and after phosphating are opposite. These results show that a high surface concentration of phosphate after activation is not sufficient for a high coverage with phosphate crystals after phosphating.