Semifluorinated Aromatic Side-Group Polystyrene-Based Block Copolymers: Bulk Structure and Surface Orientation Studies

Two families of narrow polydispersity poly(styrene)-based block copolymers bearing side groups containing both a phenyl ring and a para -linked semifluorinated side group were designed to produce stable low energy surfaces. The effects of the phenyl ring on the surface and bulk structure of the materials were investigated. The semifluorinated side chains were found to self-assemble into liquid-crystalline smectic layers within the microphase domains. An unexpected enhancement of surface organization by the aromatic group was observed. The bulk morphology and the interplay between microphase separation and liquid crystalline self-assembly were examined using transmission electron microscopy and X-ray scattering. Near-edge X-ray absorption fine structure (NEXAFS) studies were used to probe the surface coverage of the fluorinated segments. NEXAFS also allowed the determination of the orientation parameters ( S C - F and S π * ) of the C−F bond and phenyl ring of the semifluorinated side groups at the surface. On the basis of these data, the orientational coupling between the −CF 2 − helix and the aromatic ring was found to depend on the length of the fluorocarbon substituent.