Table . Summary of parameters used for the fitting of neutron reflectometry data of dry polymer brushes presented in Figures and. In comparison, PMETAI brushes displayed more hydrated structures, in particular close to the substrate (Figure and Table ). This is consistent with the quaternised structure of PMETAI and absence of protonation gradient within this brush. Therefore, stronger electrostatic repulsion within PMETAI brushes is expected to induce increased swelling. In agreement with in situ ellipsometry data, dense PMETAI brushes displayed increased swelling compared to PDMAEMA, as evaluated by the total thickness of layers containing <95% water (Table ). The homogeneity of the SLD within the brush core is also higher in the case of PMETAI compared to PDMAEMA, supporting the notion that these strong polyelectrolyte brushes display more homogenous architectures in these experimental conditions. These observations are also supported by atomistic molecular dynamics simulations that indicated that, at comparable grafting densities and chain length, PMETAI brushes swell to higher extents compared to fully protonated PDMAEMA brushes and were associated with increased uptake of water molecules . It should be noted that this was in the absence of protonation gradient as protonation states were fixed in this model.