The development of poly(9,9-dioctylfluorene) from solutions to solution processed films in terms of β-conformation: Perspective of molecular weight and solvent quality

We report how the solution structure, β-conformation and film morphology develop in poly(9,9-dioctylfluorene) (PFO) solutions and suspensions, as well as in subsequently prepared films when the molecular weight and solvent quality are systematically varied in toluene-acetone mixtures. The polymer series with molecular weights ranging from 10 kDa to 100 kDa is prepared using the precipitation fraction. The β conformation is favored by increasing molecular weight (≥30 kDa) and decreasing solvent quality (≥45 % acetone content). The content of the β conformation in the films is significantly increased when the β conformation already exists in precursor suspensions. In contrast, when there is no β conformation in the precursor solution, no β conformation will appear in the films. The mechanisms of phenomenological transformation are discussed. This work is a step toward developing quantitative guidelines for controlling PFO solutions and their film properties. [Display omitted] •β conformation of PFO is influenced by molecular weight and mixed solvent, in both solutions and films.•The β conformation and chain structure of the film are partially related to the solution.•Aggregates in solution can form sheet-like aggregates or even network.•The β content in film is higher than that in solution due to the spin-out of liquid rich in α.