Swelling of Hydrophilic Polymer Brushes by Water and Alcohol Vapors

We examine the effect of end-tethering, grafting density (σ), chemistry of polymer side chain, and solvent type on the vapor swelling of hydrophilic polymer brushes. Using a library of samples derived by postpolymerization modification of a poly­(2-(dimethylamino)­ethyl methacrylate) (PDMAEMA) brush, we determine the extent of vapor swelling and solvent uptake at different vapor pressures of water, methanol, and ethanol using spectroscopic ellipsometry. We compare the results from neat PDMAEMA and PDMAEMA quaternized by methyl iodide with chemically analogous samples prepared by spincasting bulk PDMAEMA. We find that brush samples swell to greater extents than spuncast samples, indicating a role for end-tethering in the vapor uptake process. Furthermore, vapor swelling of polymer brushes depends strongly on both polymer and solvent chemistry. We demonstrate that the extent to which σ affects vapor sorption inside the brush depends on polymer side chain chemistry, indicating an interdependence of the observed parameters on each other. The implications of these findings for the use of polymer brushes in technologies such as vapor sensing applications are discussed.