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

We report how the solution structure, beta-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 beta conformation is favored by increasing molecular weight (>= 30 kDa) and decreasing solvent quality (>= 45 % acetone content). The content of the beta conformation in the films is significantly increased when the beta conformation already exists in precursor suspensions. In contrast, when there is no beta conformation in the precursor solution, no beta 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.