Effect of solvation and concentration on F8BT chain solution behavior and film condensed structure

Abstract

Chain behavior of semi-rigid conjugated polymer in solution, correlation with condensed structure of the films and dynamic evolution in the process from solution to film are hot questions that have received close attention but have not yet solved. In this study, the scaling law obtained by laser light scattering and rheology was combined with fluorescence emission spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The chain behavior of the semi-rigid conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT, the number-average molecular weights (Mn) was 19.8 kg/mol) in solution and the condensed structure of the film were studied, the intrinsic physical relationship between the chain behavior in solution and condensed structure of the film and its dynamic evolution from solution to film were revealed. According to the concentration-dependent scaling relationship by rheology, some important parameters and chain motion characteristics in solution were revealed, such as toluene solvent was just θ solvent of F8BT, and the critical contact concentration between F8BT dilute solution and semidilute unentangled solution was found to be at 7.9 mg/mL, it firstly revealed the precursor solution concentration for film-forming (usually 10–20 mg/mL) was basically in the semidilute unentangled concentration range. The above results enrich the understanding of chain behavior in solution and the formation mechanisms of thin films condensed structure to semi-rigid conjugated polymers. The research is significant to manipulate the chain behavior in solution to construct condensed structures of the film to establish the structure-function relationship between solution state and photoelectronic device performance based on polymer physics.