Stratified Interpolyelectrolyte Complexes: Fabrication, Structure and Properties Eduardo Guzmán, Marta Ruano, Francisco Ortega and Ramón G. Rubio Abstract The electrostatic Layer-by-Layer (LbL) technique allows the fabrica- tion of polyelectrolyte multilayers that can be considered as a special type of inter- polyelectrolyte complexes supported by a template (fluid or solid). The main characteristic that confers special interest to these interpolyelectrolyte complexes is the simplicity and versatility of the method used for their fabrication, although in some cases this may hide the complex influence of the different physico-chemical variables. The possibility to change ionic strength, pH, temperature, etc. and/or the composition makes possible to control the properties and structure of these sys- tems. Furthermore, the compositional and structural richness of these systems opens multiple possibilities for the fabrication of nano-structured materials with tailored properties for numerous applications (from optical to nanomedical devi- ces). This chapter deal with the physico-chemical background of the fabrication of supramolecular films by the LbL method as well as the key properties that should be managed in order to obtain functional materials following this approach. 1 Introduction: Polyelectrolyte Multilayers and Layer-by-Layer Method The ability of the polyelectrolytes to form self-organized supramolecular structures, together to their capacity to form complexes when polyelectrolytes of opposite charge are mixed are well-known phenomena, and they have been studied from E. Guzmán (&) Istituto per l’Energetica e le Interfasi (IENI), U.O.S. Genova, Consiglio Nazionale delle Ricerche (CNR), Via de Marini 6, 16149 Genoa, Italy e-mail: e.guzman@ge.ieni.cnr.it E. Guzmán  M. Ruano  F. Ortega  R.G. Rubio Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain Ó Springer International Publishing Switzerland 2014 Visakh P.M. et al. (eds.), Polyelectrolytes, Engineering Materials, DOI 10.1007/978-3-319-01680-1_9 299