Spherical polyelectrolyte brushes

We review recent work on colloidal particles bearing a dense layer of linear polyelectrolyte chains on their surface. These systems have been termed spherical polyelectrolyte brush (SPB) because the polyelectrolyte chains have been grafted densely to the surface of the core particles. The different methods to generate such particles, namely self-assembly to form micelles, adsorption of block copolymers onto spherical colloid particles, and photo-emulsion polymerization are reviewed. The equilibrium structure of the surface layer of the particles in aqueous solution can be determined by scattering methods and electron microscopy. The structure of SPB is governed by the marked osmotic pressure of the counterions that are confined within the brush layer. This is in full accord with recent theoretical deductions discussed in detail herein. The accumulation of counterions can be used to generate metallic nanoparticles within the brush layer. The dynamics of the particles in aqueous suspension as e.g. the flow behavior in dilute solution can directly be derived from static data. Moreover, the interaction of the SPB with solid interfaces is discussed. It is demonstrated that particles bearing positively charged polyelectrolyte chains interact strongly with negatively charged surfaces. A final point discussed here is the interaction of SPB with proteins in aqueous solution. Here it is shown that these systems have a great potential as novel carrier particles for functional biomolecules. (c) 2007 Elsevier Ltd. All rights reserved.