Hierarchical structure formation of cylindrical brush polymer-surfactant complexes

The complex formation of cylindrical brush polymers with poly(l-lysine) side chains (PLL) and sodium dodecyl sulfate (SDS) can induce a helical conformation of the cylindrical brush polymer in aqueous solution (Gunari, N.; Cong, Y.; Zhang, B.; Fischer, K.; Janshoff, A.; Schmidt, M. Macromol. Rapid Commun. 2008, 29, 821-825). Herein, we have systematically investigated the influence of surfactant, salt, and pH on the supramolecular structure formation. The cylindrical brush polymers and their complexes with surfactants were directly visualized by atomic force microscopy in air and in aqueous solution. The alkyl chain length (measured by the carbon number, n) of the surfactant plays a key role. While helical structures were formed with n=10, 11, and 12, no helices were observed with n<10 and n>13. Addition of salt destroys the helical structures as do pH conditions below 4 and above 6, most probably because the polymer-surfactant complexes start to disintegrate. Circular dichroism was utilized to monitor the PLL side chain conformation and clearly revealed that beta-sheet formation of the side chains induces the helical conformation of the atactic main chain.