Properties of pH-Responsive Mixed Aggregates of Polystyrene-block-poly(L-lysine) and Nonionic Surfactant in Solution and Adsorbed at a Solid Surface

Poly(styrene)(388)-block-poly(L-lysine)(138) could be dispersed in water with the aid of the nonionic surfactant C12E6. Light scattering and direct imaging techniques show that the copolymer/surfactant aggregates are polydisperse spherical micelles. The rather broad size distribution can be attributed to the glassy state of the polystyrene core of the micelles hampering equilibration. Nevertheless, the poly(L-lysine) block remains pH sensitive in these mixed aggregates and circular dichroism measurements show that poly(L-lysine) block adopts a random coil conformation at low pH and an beta-sheet conformation at pH >= 11 without any change in the micellar shape. Samples prepared by evaporation of drops of the solutions on graphite wafers exhibit different wetting patterns depending on the polypeptide conformation as indicated by atomic force microscopy.