A new model for neutron reflectometry of adsorbed surfactant aggregates

A new interpretation of neutron reflectivity data for surfactants adsorbed on hydrophilic solid surfaces has been developed. Motivated by recent atomi c force microscopy results, a model of the adsorbed layer is constructed ba sed upon an adsorbed layer consisting of discrete, micelle-like surfactant aggregates of well-defined geometries. Scattering length density profiles a nd reflectivity curves are calculated for conventional, laterally unstructu red adsorbed layers (a bilayer), as well as for cylindrical and spherical s urfactant aggregates adsorbed on a hydrophilic surface. It is shown that tr eating such structured surfactant films as bilayers often results in a good fit to neutron reflectivity data, but that fit parameters lead one to unde restimate the film thickness and overestimate the fractional surface covera ge by the adsorbed film.