The Stability of Silica Hydrosols Under the Influence of Polymer Adsorption

The stability of standardized, well dispersed silica (Aerosil). hydrosols at different pH has been studied using a self-constructed laser photosedimentometer. Ultrasonication was proved most suitable for providing reproducible standardized hydrosols, which were characterized by determining the viscosity/concentration dependence in a cylinder viscosimeter, the sedimentation coefficient in an analytical ultracentrifuge, the partial specific volume in an oscillating U-tube of a high precision density meter, the translational diffusion coefficient with a photon correlation spectrometer and the dimension and shape of the silica particles by transmission electron microscopy. The Aerosil hydrosols can be reproducibly flocculated with polyethyleneglycols of molar mass 6000 and 40 000, even in the absence of electrolyte at high pH, when the sol concentration is sufficiently high. Reproducibility necessitates standardized mixing procedures of sol and polymer. The laser-photosedimentometer provides suitable parameters for the characterization of the turbidity- and sedimentation behaviour of the flocculated sols. The effects of different mixing procedures have been tested and the influence of titration and mixing time, intensity and time of stirring can be analyzed quantitatively as well, as the relationships of the characterizing parameters on polymer coverage, molecular weight and silica concentration. From these dependences and by using additional rheological measurements it was possible to identify the classical model of polymer bridging as the most likely mechanism for the destabilizatio

The Adsorption of Macromolecules on Solid/Liquid Interfaces

The main problem in the investigations of polymer adsorption is clearing up the structu,re of the adsorbed layer, and the conformation of the adsorbed macromolecule. In order to get direct informations of the adsorbed macromolecule, calorimetric, ellipsometric and ir-spectrometric measurements are used. The structure of the polymer layer of the investigated polymer-solvent-adsorbens system is characterized by the adsorbed amount, the number of adhesive segments, the adsorption enthalpy and by the thickness and the concentration of the adsorbed layer. All this parameters are dependent on the structure of the macromolecule in solution, the degree of coverage of the adsorbent surface, the enthalpy balance and the surface density of the adhesive sites on the adsorbens. The reversibility of the adsorption is influenced by the conformation of the adsorbed macromolecule and by the molecular weight

Der Mechanismus des Wasserstoffdeuteriumaustauschs an Nickel.

Diss. München.OPLADEN-RUG0