Thin film morphologies of block copolymers complexed with wedge-shaped liquid crystalline amphiphilic molecules
Wedge-shaped molecules with a sulfonic group at the tip have been incorporated into a poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP-b-PEO) diblock copolymer via proton transfer at different degrees of neutralization. The protonation of P2VP was monitored by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The thin film morphology of the complexed block copolymers has been studied by scanning force microscopy and X-ray reflectivity. The complexes exhibit strongly microphase-segregated patterns comprising smectic layers of the complexed P2VP blocks, oriented parallel to the substrate throughout the whole film with the embedded PEO domains. For the complex with a degree of neutralization of 0.50 ordered amorphous PEO cylinders are observed oriented perpendicular to the substrate. For a degree of neutralization equal to 0.25 initially also perpendicular PEO cylinders are formed, but upon solvent-vapor annealing they partially merge, resulting in a mixed lamellar-cylindrical morphology. In all cases an extra surface layer is formed at the substrate. Thus, for the first time we have demonstrated that a block copolymer thin film structure can easily be controlled by the degree of neutralization of one of the blocks.
Albrecht, K, Mourran, A, Zhu, X, Markkula, T, Groll, J, Beginn, U, … Möller, M. (2008). Thin film morphologies of block copolymers complexed with wedge-shaped liquid crystalline amphiphilic molecules. Macromolecules, 41, 1728–1738. doi:10.1021/ma071317n