The total swollen thicknesses measured were also in excellent agreement with the swelling factors measured by ellipsometry in PBS (2.73 ± 1.2% for PDMAEMA; 2.35 ± 4.3% for PMETAC; Figure ). Following the successful multi-contrast fitting of the data obtained for pristine swollen brushes, the same model (4 brush layers and 1 silicon oxide layer) was applied to all polymer brushes studied. The silicon oxide layer, determined independently for each substrate, was kept mostly constant following subsequent fits, only allowing minor changes to account for some of the changes seen at high Q values in some of the samples studied (see full details of parameters used in respective tables).