Is Osmotic Pressure Relevant in the Mechanical Confinement of a Polymer Brush?

The structures of polymer brushes under confinement were measured using a combination of neutron reflectivity and a surface force type apparatus. The samples were either poly­(ethylene oxide), PEO, used to investigate the effect of the grafting density or poly­(acrylic acid), PAA, used to determine the effect of charge on the structure of a polymer brushes under confinement. Without confinement both PEO and PAA brushes are found to be highly swollen with water, >50% v/v, with the expected parabolic brush structure. Compression of the PEO brushes with as little as 0.5 bar of confinement is found experimentally to reduce the brush to a polymer block of uniform density that is significantly dehydrated,