Ideal spread monolayer formation and surface pressure induced orientation in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) via hybridized with liquid crystal molecule on water

Hydrophobic Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) [F8BT] formed an ideal spread monolayer on a water surface by the cospreading method with liquid crystal molecule, 4′-pentyl-4-cyanobiphenyl [5CB]. The F8BT/5CB hybrid monolayers were characterized by surface pressure-area (π-A) isotherm measurements and atomic force microscopy (AFM). F8BT does not form a homogeneous monolayer by direct spreading on water from a single solution. The mixed film of two components, F8BT and 5CB, gave a characteristic pressure lift-off attributed to the hybrid monolayer above the 5CB plateau. AFM observation revealed that the spread monolayer of the F8BT formed on the top of the 5CB monolayer on water with the thickness of ca. 1.7 nm. The F8BT/5CB hybrid monolayers could be fully transferred onto a solid substrate, and pure F8BT monolayers were obtained after volatilization of 5CB by gentle heating. Polarized UV-vis absorption spectra showed that the main chain of F8BT preferentially oriented perpendicular to the compressive direction at the surface pressure of 10 mN m−1 on water.