The neutron reflectivity profiles of all brushes displayed clear fringes that reflected changes in their thickness (Figure ). These could be fit satisfactorily with bilayer models of silicon oxide and polymer brushes with scattering length densities of 0.913 × 10 -6 and 0.5 × 10 -6 Å -2 for PDMAEMA and PMETAI respectively, apart from the lower density PDMAEMA brushes that required lowering of the SLD to 0.82 × 10 -6 Å -2 . This is consistent with the increased roughness of low density brushes , resulting in overall lower scattering length densities when averaged over a macroscopic surface area. Parameters extracted from the fits of dry brushes are presented in Table . The dry thicknesses extracted are in excellent agreement with those measured by ellipsometry, taken into account the thickness of the initiator layer (typically measured by ellipsometry in the range of 1.0-2.0 nm). and the silicon block. Details of the parameters used can be found in Table .