Polymer Mediated Surface Forces

Sammanfattning: The issue of controlling the stability between colloidal particles in solution is important, at least for industrial applications, relying on efficient flocculation or stable dispersions. The objective of this thesis is to shed some light on fundamental mechanisms behind the interplay between attractive and repulsive forces, in solutions containing colloids and polymers. We approach the problem from a theoretical point of view, developing powerful simulation techniques dealing with polymeric systems. In particular we mimic effects of full equilibrium situations, wherein polymers are allowed to diffuse between a narrow slit and a surrounding bulk solution. We observe long ranged electrostatic repulsions in confined polyelectrolyte solutions, as well as oscillatory surface forces. This seems to be coupled with a strong polyelectrolyte chain affinity to the surfaces, leading to an appreciable degree of surface charge inversion. Effects of increasing the intrinsic chain stiffness are also studied, revealing a crossover between two fundamentally different mechanisms of attraction, namely polymeric bridging and charge-charge correlation. Hard sphere polymer systems are also investigated with focus on varying monomer-surface affinities, bulk concentrations and chain architectures.