Polyelectrolyte brushes: Understanding Multivalent Effects on Structure and Properties

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We propose to study the structure and interaction of polyelectrolyte brushes in presence of multivalent counterions and oppositely charged surfactants. Polyelectrolyte brushes result if long polyelectrolyte chains are grafted to planar surfaces or to colloidal spheres (spherical polyelectrolyte brush). In this way a dense layer of highly charged polymeric chains results that has unique properties. In particular, the counterions balancing the charge of the polyelectrolyte chains are mostly confined within the polyelectrolyte layer in salt-free solution. Adding more and more salt, however, screens the charges and the polyelectrolyte brushes have properties similar to uncharged surface layers of polymers. We plan to study these unique systems in presence of multivalent ions and hydrophobic counterions. Work done by the applicants has shown that the brush layer collapses under these conditions and two such layers may even attract each other. In order to elucidate this in detail, the group of M. Tirrell (UC Santa Barbara) will study planar polyelectrolyte brushes whereas the group of M. Ballauff (University of Bayreuth) will investigate spherical polyelectrolyte brushes. The group of P. Pincus (UC Santa Barbara) will develop theoretical models for both systems. All groups will closely collaborate and exchange students for a prolonged time. We hope to achieve a full understanding of the structure and interaction of these systems.