Are sprayed LbL-films stratified? A first assessment of the nanostructure of spray-assembled multilayers by neutron reflectometry

We describe first neutron reflectometry experiments on spray-assembled polyelectrolyte multilayer films containing regularly spaced layers of perdeuterated poly(styrene sulfonate). From samples containing either only non-deuterated layers or containing a maximum of deuterated layers we obtain all model parameters (thicknesses, scattering length densities and roughnesses) required for calculating the reflectivities of multilayer films with a regular superlattice structure. For two different superlattice films we show that we obtain an excellent match between experimental data and calculated reflectivities without any free fit parameter. Our data clearly demonstrate that spray-assembled polyelectrolyte multilayers are indeed stratified although some structural parameters differ enormously from films prepared by classic dipping. Our present experiments confirm a substantial difference in thickness and suggest a reduced interfacial roughness in spray-assembled films.