Bi-axially aligned crystallites of a fluorene–bithiophene co-polymer

Thin films of the soluble conjugated poly(9,9-dioctylfluorenyl-co-bithiophene) (F8T2) on top of polyimide surfaces were investigated by X-ray diffraction measurements, atomic force and optical microscopy. In-situ temperature dependent specular X-ray diffraction experiments reveal the formation crystallites on heating. An orthorhombic unit cell of a = 1.61 nm, b = 1.28 nm and c = 6.2 nm was found which results in 16 monomer units being hosted in the unit cell at a density of 1.15 g cm−3. Morphology investigations reveal random azimutal orientations of spherulite like structures are present for samples prepared on the isotropic surface. Using a defined preparation route allowed for the alignment of the crystallites with respect of a rubbed polyimide surface resulting in bi-axially aligned F8T2 crystals as determined by X-ray diffraction polefigure measurements and optical microscopy.

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► A thermic crystal phase of a fluorene–thiophene co-polymer (F8T2) is identified.
► A packing of the polymer backbone is proposed.
► The preparation of uni-axially F8T2 is presented.
► A route for the preparation of bi-axially aligned F8T2 is shown.
► Polefigures reveal azimuthal order with respect of the uni-axially aligned F8T2.