Editorial Special issue on Polyelectrolytes

At the launch of the Soft Matter part of the European Physical Journal EPJ E, we insisted on two points: the journal should be interdisciplinary and accessible to the various communities working on Soft Condensed Matter, primarily physicists, physico-chemists and chemists but also biophysicists; it should also become a forum where important and controversial issues are debated. Two proposals have emerged to push these ideas forward, the publication of perspectives or commentaries on articles that raise important issues and of special issues on topics of broad interest for the whole community. The first of our special issues is on "Polyelectrolytes". This is a subject of active research in particular because of the numerous applications of polyelectrolytes as water-soluble polymers and as biomaterials and it should be of interest for a large part of the community targetted by EPJ E. For this issue, we have invited a few articles and added several regular articles that fitted well into the subject. In order to avoid too long publication delays, some of the manuscript that we intended to include have already been published as regular articles and some late manuscripts will be published in forthcoming issues of the journal. Nevertheless, we feel that we have here a representative collection of manuscripts spanning various aspects of research on polyelectrolytes. A large proportion of the papers in this issue deals with the interfacial behavior of polyelectrolytes. This is certainly indicative of the very large effort currently made in this area. The main aspects are: fundamental studies of polyelectrolyte adsorption, polyelectrolyte brushes, polyelectrolytes trapped in soap films, polyelectrolyte multilayers and a theoretical description of polyampholyte adsorption. The other papers deal with the synthesis of copolymers with ampholyte blocks and various aspects of polyelectrolyte solutions (associating polyelectrolytes and complexation by multivalent ions). We hope that this issue will be useful in stimulating debate on some of the ideas raised and that it will help to strengthen the links between the various communities