Formation of single-crystal-like poly(9,9-dioctylfluorene) thin film by the friction-transfer technique with subsequent thermal treatments

A liquid-crystalline polymer, poly(9,9-dioctylfluorene) (PFO), was found to form highly oriented films by a friction-transfer technique. The polarized UV-vis absorption and photoluminescence spectra of the films formed showed strong dichroism with a dichroic ratio of approximately 10 in the drawing direction of friction transfer. Subsequent thermal treatments of the friction-transferred PFO films were specifically effective for the improvement of the physical properties, structure, and morphology of the films. By rapid and slow cooling from the liquid-crystalline melted states of the friction-transferred films, liquid-crystalline and crystalline films were prepared, respectively. Both thermally treated films showed enhanced optical anisotropy with a dichroic ratio of approximately 25 in photoluminescence spectra. The electron diffraction pattern of the crystalline film showed a large number of sharp diffraction spots as seen in a single crystal. The liquid-crystalline polymer was found to form a single-crystal-like thin film by the friction-transfer technique with subsequent thermal treatments.