An In Situ Investigation into the Formation of the Solvent‐Induced Crystalline Phase of Poly(9,9‐Dioctylfluorene) in Solvent Vapor Annealing

Abstract

A new metastable solvent‐induced clathrate liquid crystalline phase of β phase (named β' here) in crystalline poly(9,9‐dioctylfluorene) (PFO) thin film induced by solvent annealing is found by a combination of in situ ultraviolet and visible spectrophotometry (UV‐vis), photoluminescence spectroscopy (PL), and grazing incidence wide‐angle X‐ray scattering (GIWAXS). The solvent annealing process consists of three processes: diffusion of solvent molecules into the film; saturation of solvent in the film; and drying of the film under nitrogen. The formation of β' phase with ordered packing of side chains and disordered packing of backbones occurs during the diffusion process of solvent molecules into the film. When the solvent molecules penetrate the film, the disordered side chains start to align themselves to form an ordered structure, and the ordering would gradually in the saturationprocess. Furthermore, the ordering of side chains drives an ordered rearrangement of the backbones during the drying process; however, the crystallinity of the side chains decreases with the orderly rearrangement of backbones due to the helical conformation of PFO. image