Polymer brushes under flow and in other out-of-equilibrium conditions

Polymer brushes are formed from flexible linear macromolecules tethered at one chain end to a solid substrate, forming a dense polymeric layer of polymer chains which are more or less stretched in the direction perpendicular to the substrate surface. These systems find interest also due to numerous applications (colloid stabilization, improvement of lubrication properties when the surfaces are exposed to shear, protection of the surface against adsorption of nanoparticles or proteins, etc.), for which often the dynamic non-equilibrium response of these brushes to external perturbation is important. The present review summarizes recent computer simulation studies pertinent to these questions. Polymer brushes exposed to shear due to flow of the solvent or a polymer melt the brush interacts with are discussed, and the friction between two brushes is discussed. Another topic that is emphasized is the interaction of polymer brushes with "nanoinclusions'' (i.e., small colloidal particles or linear macromolecules down to oligomers), discussing the absorption or expulsion of these objects, and again the response to shear. The simulations are interpreted in terms of scaling concepts and other phenomenological theories wherever possible, and an outlook to related experiments is given.