Neutron reflectometry study of the segment-density profiles in end-graftedand irreversibly adsorbed layers of polymer in good solvents

The segment density profile of anchored layers of poly(dimethylsiloxane) in good solvents has been measured using neutron reflectometry. Two types of layers have been studied: end-grafted layers (brushes) and irreversibly ads orbed layers, on silicon/silicon dioxide. The latter can be viewed as a pol ydisperse brush of loops and was obtained by adsorbing the polymer from the melt or from a concentrated solution. A model-free constrained fitting pro cedure was developed, which gave the concentration profile with a good prec ision. We present this numerical method and the concentration profiles obta ined for the different layers. The profiles of the two types of layers are significantly different. They are in agreement with self-consistent mean fi eld theory for the brushes and with scaling laws descriptions for the irrev ersibly adsorbed layers. The reflectivity measurement enabled us to verify precisely that the concentration profile in the brush cannot be described b y a step function with a Gaussian roughness but has a parabolic shape.