We are investigating the mechanism of adsorption of complexes formed from oppositely charged polyelectrolyte and surfactant on to hydrophilic and hydrophobic surfaces. After addition of formulation the amount adsorbed increases until steady state is achieved. After steady state, the bulk is diluted which initiates a second period of maximal adsorption. In the dilution step, the complexes in the bulk coacervate which causes the secondary adsorption. Our main objective is to study the composition of the adsorbed surface layer. This will assist in our modelling of the mechanism of adsorption, particularly the secondary adsorption of maximal adsorption. This is due to the fact that the rate of adsorption will be governed by the composition dependent charge state of pre-adsorbed polymer-surfactant layer as well as the charge state of the bulk complexes. Different dilution regimes have been designed to modulate the rate of coacervation in the bulk and charge state of the surface layers to further refine our mechanistic kinetic models. Neutron contrast variation will enable the composition to be determined kinetically in different adsorption regimes and in the steady state films.