Polyelectrolyte adsorption onto an oppositely charged interface is determined by electrostatic and secondary interactions. Since polyelectrolytes precipitate at elevated temperatures, the secondary interactions are presumably temperature dependent. This idea is tested for poly(allylamine) hydrochloride/ polystyrene sulfonate (PAH/PSS) films adsorbed from aqueous KCl solution (high salt conditions) at temperatures between 5 and 40 °C. KCl was chosen because the films were thicker than those obtained from NaCl or CsCl solutions indicating strong specific binding between K and PSS. The film thickness increases continuously with the adsorption temperature; the changes amount to 20-40%, depending on salt conditions. Furthermore, the roughness is increased, up to a factor of 5. The latter is attributed to the decreased percentage of strong electrostatic bonds within the polyelectrolyte multilayer. Another path to increased roughening is using low-weight polymers with a contour length similar to the thickness of a polycation/polyanion pair.

A 'particle interaction apparatus' based on the technique of atomic force microscopy was constructed that allows us to measure the interaction between single micron-sized particles and the air-water interface. From the force versus distance profiles ('force curves') the contact angle of single microspheres could be determined. This new method for microsphere tensiometry was validated using a variety of materials with contact angles between 20 • and 90 • . Contact angles measured on single microspheres correlated well with those measured on flat substrates of the same materials.The interaction of single silica microspheres with an air bubble in the presence of surfactants (SDS and DTAB) was investigated. Depending on surfactant type and concentration, adhesion or repulsion could be induced. Adhesion forces were found to depend on the applied load, indicating possible adsorption/desorption processes at the particle-bubble interface.We have built a new set-up that combines a particle interaction apparatus with a Langmuir trough and a fluorescence microscope. This will allow study of interactions at the air-water interface in more detail, especially in the presence of a definite surface density of amphiphilic molecules.The interaction of single ZnS spheres with a bubble (modelling flotation of ZnS) was studied at different pH values. The results suggest that the isoelectric point of these spheres exists between pH 7 and 8.

Experiments were carried out on a water-based ferrofluid (gamma-Fe2O3 with carboxydextran shell) using photon correlation spectroscopy (PCS), atomic force microscopy, and magnetic nanoparticle relaxation measurements. The experiments were designed with the aim to relate the Néel signals that are in theory generated by large single core particles with nanoscopic properties, that is, particle size, particle size distribution, shell properties, and aggregation. For this purpose, the ferrofluid was fractionated by magnetic fractionation and size exclusion chromatography. Nanoparticles adsorbed onto positively charged substrates form a two-dimensional monolayer. Their mean core diameters are in the range of 6 to about 20 nm, and particles above 10 nm are mostly aggregates. The hydrodynamic particle diameters are between 13 and 80 nm. The core diameter of the smallest fraction is confirmed by X-ray reflectometry; the surface coverage is controlled by bulk diffusion. Comparison with the hydrodynamic radius yields a shell thickness of 3.8 nm. Considering the shell thickness to be constant for all particles, it was possible to calculate the apparent particle diameter in the original ferrofluid from the PCS signals of all fractions. As expected, the small cores yielded no Néel relaxation signals in freeze-dried samples; however, the fractions containing mostly aggregates yielded Néel relaxation signals.

We investigate the self‐organization of PSS in brushes and polyelectrolyte multilayers with X‐ray, neutron and optical reflectivity. The electrostatic force dominates brush phases and adsorption behavior, additionally we find evidence of a strong hydrophobic force: (ι) within amphiphilic diblock copolymer monolayers, a PSS monolayer adsorbs flatly to the hydrophobic block, (ιι) on temperature increase (and with screened electrostatic forces), more PSS is adsorbed onto oppositely charged surfaces, and (ιιι) a polyelectrolyte multilayers shrinks when heated at 100% r.h. The latter two effects are consistent with the well‐known increase of the hydrophobic force on heating: The increased PSS surface coverage can be attributed to deteriorating solvent conditions. Within a polyelectrolyte multilayer, an increase of the hydrophobic force maximizes the local contact of hydrophobic polymer segments, causing a reduction of swelling and an increased mass density.