Adsorbed and Grafted Polymers at Equilibrium

Abstract

This chapter deals with various aspects related to the adsorption of long chain-like macromolecules (polymers) onto solid surfaces. Physical aspects of the adsorption mechanism are elaborated mainly at thermodynamical equilibrium. The basic features needed in modeling of this adsorption are discussed. We first discuss the adsorption of a single and long polymer chain to the surface. The surface interaction is modeled by a potential well with a long-ranged attractive tail. A simple mean-field theory description is presented and the concept of polymer "blobs" is used to describe the conformation of the chain at the surface. The thickness of the adsorbed layer depends on several polymer and surface parameters. Fluctuation corrections to mean-field theory are also discussed. We then review adsorption as well as depletion processes in the many-chain case. Profiles, changes in the surface tension and polymer surface excess are calculated within mean-field theory. Corrections due to fluctuations in good solvent are taken into account using scaling concepts. The proximal exponent is introduced in analogy to surface critical phenomena. The interaction between two surfaces with adsorbed polymer layers is discussed, and various cases leading to attractive and repulsive interactions are mentioned. Polyelectrolytes are of practical importance due to their water solubility; we give a short summary of recent progress in this rapidly evolving field. The behavior of grafted polymers, i.e., polymers which are anchored with one end to a solid substrate is also reviewed.