title: Gelation behavior of poly(9,9-dioctylfluorene)/poly[9,9-di(2-ethylhexyl)-fluorenyl-2,7-diyl] blend in methylcyclohexane solutions.
abstract: We investigated the gelation behavior of the blend of two light-emitting polyfluorenes, i.e., poly(9,9-dioctylfluorene-2,7-diyl) (PF(8)) and poly[9,9-di(2-ethylhexyl)-fluorenyl-2,7-diyl] (PF(2/6)), in  solutions with methylcyclohexane (MCH). Upon prolonged aging at room temperature, dynamic light scattering revealed that phase separation in the initially well-mixed solutions occurred via  spinodal decomposition, yielding a PF(8)/PF(2/6)-enriched phase and an isotropic solvent-rich phase. Sheetlike aggregates in which a portion of the PF(8) chains adopted the β conformation were formed in the polymer-enriched phase, as revealed by small-angle X-ray scattering and optical spectroscopy. Macroscopically, the phase separation transformed the original viscous liquid solution into a gel. Measurements of the gelation temperature (T(gel)), gel-to-sol transition temperature (T(g-s)), and spinodal decomposition temperature (T(SD)) indicated that  gelation (and hence  phase separation) became more difficult with increasing content of PF(2/6). The presence of PF(2/6) also hindered  formation of the β-phase of PF(8.) Therefore, the microstructure and photophysical properties of PF(8)/PF(2/6) in MCH solution can be tuned by the composition of the two polymers.
authors.affiliation: Department of Materials Engineering, Kun Shan University, Tainan 71003, Taiwan. kelvench@mail.ksu.edu.tw
authors.forename: Jean-Hong
authors.initials: JH
authors.lastname: Chen
authors.forename: Ching-Iuan
authors.initials: CI
authors.lastname: Su
authors.forename: Hsin-Lung
authors.initials: HL
authors.lastname: Chen
authors.forename: Chih-Shun
authors.initials: CS
authors.lastname: Chang
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Chang
authors.forename: Lung-Chuan
authors.initials: LC
authors.lastname: Chen
authors.forename: Show-An
authors.initials: SA
authors.lastname: Chen