The properties and phase behavior of a binary mixed polymer brush have been studied. The brush system was constructed by adsorption of amphiphilic diblock copolymers to the air-water interface. The hydrophobic anchoring block was chosen to be poly(n-butyl acrylate) (PnBA) because it possesses favorable wetting properties with water and is non-glassy at room temperature. These two properties eliminate the difficulties of kinetically frozen surface micelles such as are seen in the classic polystyrene-b-poly(ethylene oxide) system. Instead a uniformly smooth surface is formed. The brushes are composed of poly(ethylene oxide) (PEO) a surface active hydrophilic polymer and poly(dimethylamino ethylmethacrylate) (PDMAEMA) which has weakly associating amine groups which can become positively charged in aqueous solution. The surface pressure isotherms are measured for both single component and mixed brush systems as functions of salt concentration, pH, and polymer mole fraction. These results are compared to a numerical self-consistent field (SCF) theory that includes the contributions to the free energy from the hydrophobic anchoring block . Finally, the phase behavior of the mixed brush system is visualized using fluorescence labeling. Our previous SCF calculations predict that chemically incompatible polymer brushes will phase separate at small area per chain and low effective charge on the polyelectrolytes.1 We here elucidate under what conditions this separation can be macroscopic or microscopic in scale.

1. Witte, K. N.; Won, Y. Y. Macromolecules 2006, 39, (22), 7757-7768.