Neutron reflectivity of end-grafted polymers: Concentration and solvent quality dependence in equilibrium conditions

Neutron reflectometry is used to obtain a direct measurement of the monomer distribution of a weakly bound end-grafted polystyrene layer in equilibrium with bulk solution, as a function of the polymer concentration and temperature. We report for the first time two new regions in the density profile of the polymers, an excess polymer near the surface and a wetting layer on top of the brush. The physical properties of the polymer layer are strongly affected by the equilibrium between the bound and free polymer molecules.