文摘
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 lessviscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10-100 nm) sheetlike assemblies (thicknessof 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 witha putative double layer structure. PF10 does not follow this sequence, and only part of the polymer is assembledinto a sheetlike structure, the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixturesalso have lower length scale crystalline structures with an internal period corresponding to the periodicity observedin 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 inthe phase, while this is not observed with other polymer/MCH systems.
