Structure of physically adsorbed polymer layers measured by small-angle neutron scattering using contrast variation methods

The scattering from poly(ethylene oxide) adsorbed on polystyrene latex particles was measured as a function of the isotopic composition of the aqueous solvent. Oscillations in the data were observed even when the particle was matched in scattering length density to the solvent. These oscillations are a new and important characteristic of the scattering from an adsorbed polymer layer compared to the scattering from free chains. The contrast variation approach allowed the scattering from the interference between the layer and the particle to be measured explicitly. The data have been fitted using a model function to find the volume fraction profile of the adsorbed layer without the complications that can arise from density-fluctuation contributions to the scattering. It was therefore possible to obtain the fluctuation contribution itself by simple subtraction. The fluctuation scattering was found to be in good agreement with scaling predictions and with a new function derived for an exponential volume fraction profile.