We study the equilibrium and structural properties of mixtures of like-charged colloids and nonadsorbing flexible polyelectrolytes using liquid state integral equations. The polymer chains in the semidilute regime are treated within the polymer reference interaction site model. The monomers and the colloids interact via screened Coulomb potentials (Debye–Hückel level). The electrostatic interactions between the different macromolecules inside the solution are responsible for complex local structures and rich phase diagrams, which depend on the charges and on the Debye screening length. The pair correlations between colloids are interpreted in terms of the effective, polymer-averaged, colloid–colloid pair potential. A first-order picture indicates that the Coulombic depletion attraction due to the osmotic pressure of the semidilute network against the colloidal particles dominates the direct repulsion at high enough monomer concentration and induces the liquid–liquid phase separation. Higher-order effects involving correlations inside the polyelectrolyte system alter this simple picture.

We use a simple cellular automata type model to describe the role of diffusion and reaction processes in the formation of films on a surface. At a mesoscopic scale we select three main processes present during the formation of real interfaces: the corrosion of the metal at the corrosion front, the redistribution of the intermediate corrosion products across the layer already formed, and their precipitation at the growth front. The redistribution of the intermediate corrosion products is modeled as a diffusion of a chemical species. As the concentration of this species at the corrosion front can be large, we have to consider their interactions which is the new aspect of this model. As a result we have a feedback effect on the evolution and structure of the corrosion front. We show that the initial corrosion rate is progressively decreased to the corrosion rate limited by the diffusion process. The corrosion front becomes flat and loses the fractal character present in the corresponding model without the feedback effect. The flattening of the corrosion front increases the protective effect and slows down the corrosion rate. Thus, the overall passivation results from a combination of these two effects. The simple exclusion principle adopted in the model leads to highly nonlinear couplings between the processes involved. The nonlinear dynamics is seen in the time dependence of the diffusing species profile across the layer.

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