Abstract
We report on the phase behavior of poly(9,9-dihexylfluorene) (PF6), poly(9,9-diheptylfluorene) (PF7), poly(9,9-dioctylfluorene) (PF8), poly(9,9-dinonylfluorene) (PF9), and poly(9,9-didecylfluorene) (PF10) in methylcyclohexane (MCH). After a heating-cooling cycle, in the 10-50 mg/mL concentration range, PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH systems were found to be gel-like, while PF10/MCH appears less viscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10-100 nm) sheetlike assemblies (thickness of 2-3 nm). The larger length scale structures of these sheets show an odd-even dependence on the side chain (spacer) length: the PF6 and PF8 sheets are broader and thinner, whereas PF7 and PF9 sheets are thicker with a putative double layer structure. PF10 does not follow this sequence, and only part of the polymer is assembled into a sheetlike structure, the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixtures also have lower length scale crystalline structures with an internal period corresponding to the periodicity observed in the solid-state phase of PF8. Vestiges of crystalline domains are found for PF6 and PF7 but not for PF10. PF7/MCH, PF8/MCH, and PF9/MCH systems contain the conformational isomer C, of those chains observed in the phase, while this is not observed with other polymer/MCH systems.
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