Multiple orientation and nematic-hexagonal transition in uniaxially aligned polyfluorene thin films

Matti Knaapila; Benjamin P. Lyons; Kaisa Kisko; Oliver H. Seeck; Joel P. Foreman; Ulla Vainio; Ritva Serimaa; Mika Torkkeli; Andrew P. Monkman

doi:10.1117/12.555823

10 November 2004 Multiple orientation and nematic-hexagonal transition in uniaxially aligned polyfluorene thin films

Matti Knaapila, Benjamin P. Lyons, Kaisa Kisko, Oliver H. Seeck, Joel P. Foreman, Ulla Vainio, Ritva Serimaa, Mika Torkkeli, Andrew P. Monkman

Author Affiliations +

Proceedings Volume 5519, Organic Light-Emitting Materials and Devices VIII; (2004) https://doi.org/10.1117/12.555823
Event: Optical Science and Technology, the SPIE 49th Annual Meeting, 2004, Denver, Colorado, United States

Abstract

We present a structural study of poly(9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl) (PF2/6) in aligned thin films on a rubbed polyimide substrate. PF2/6 forms 5/2-helical hairy-rodlike molecular structure which is self-organized in the hexagonal structure. In thin films, the aligned rigid polymer chains are parallel to the substrate in the direction corresponding to the molecular backbone, c axis. The cells are flattened in the direction of the surface normal and -in particular- reveal a multiple orientation where the greater proportion of the crystallites have one crystal axis a perpendicular to the substrate surface but a small proportion are aligned with the crystal axis a parallel to surface. We find further that by reducing the polymer chain length to approximately twenty repeat units the degree of axial alignment of PF2/6 is considerably improved while the local order changes from hexagonal packing towards nematic phase with no sign of multiple orientation.

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Matti Knaapila, Benjamin P. Lyons, Kaisa Kisko, Oliver H. Seeck, Joel P. Foreman, Ulla Vainio, Ritva Serimaa, Mika Torkkeli, and Andrew P. Monkman "Multiple orientation and nematic-hexagonal transition in uniaxially aligned polyfluorene thin films", Proc. SPIE 5519, Organic Light-Emitting Materials and Devices VIII, (10 November 2004); https://doi.org/10.1117/12.555823

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