Polyelectrolyte brushes: Understanding Multivalent Effects on Structure and Properties

我们建议研究多价反离子和带相反电荷的表面活性剂存在时聚电解质刷的结构和相互作用。如果将长聚电解质链接枝到平面表面或胶体球（球形聚电解质刷）上，就会产生聚电解质刷。通过这种方式，高电荷聚合链的致密层具有独特的性能。特别是，在无盐溶液中，平衡聚电解质链电荷的反离子大多被限制在聚电解质层内。然而，加入越来越多的盐会屏蔽电荷，聚电解质刷具有类似于不带电的聚合物表面层的特性。我们计划在多价离子和疏水反离子存在的情况下研究这些独特的体系。申请人所做的工作表明，在这些条件下，刷层会坍塌，两个这样的层甚至会相互吸引。为了详细阐明这一点，来自加州大学圣巴巴拉分校的M. Tirrell团队将研究平面聚电解质刷，而来自拜罗伊特大学的M. Ballauff团队将研究球形聚电解质刷。来自加州大学圣巴巴拉分校的P. Pincus团队将为这两个系统开发理论模型。各小组将密切合作，长期交换学生。我们希望对这些系统的结构和相互作用有一个全面的了解。

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.