Poly (N-isopropyl acrylamide) brush topography: relationship to film collapse and protein adsorption

Atomic force microscopy was used to image the topography of poly (N-isopropyl acrylamide) brushes end-grafted from initiator-terminated alkane monolayers on gold or on silicon wafers. Measurements were done in air and in water, below and above the lower critical solution temperature of 32°C. At low grafting densities and molecular weights, area-averaged ellipsometry, surface force, and neutron reflectivity measurements did not detect volume changes in the wet polymer brushes above 32°C. However, atomic force microscopy images of the same films reveal surface features that suggest the formation of lateral aggregates or “octopus micelles”. At high grafting densities, the polymer films collapse uniformly. This temperature-dependent swelling and collapse was compared with ellipsometry data and with protein adsorption behavior