The strong interaction between polyelectrolytes and ionic surfactants can result in pronounced surface adsorption and the formation of surface multilayer structures. This results in important surface properties with potential applications in detergency and in soft lubrication. In this context polyethyleneimine, PEI, based polyelectrolytes are particularly attractive, and although ethoxylation can fine tune the interactions any enhancement in the adsorption is greatly reduced. We have shown recently (Langmuir 30, 2014, 9761) that the nature of the ethoxylation can be adjusted such that the favourable surface properties are retained. In order to optimise the interaction of the surfactant with the ethoxylated PEI it is now essential to understand the structure of the surface layer in detail.