To improve alignment of isoindigo-based conjugated polymer film by controlling contact line receding velocity

The macroscopic alignment of conjugated polymers with low grain boundary is essential to carrier transport. During film forming process, the match between contact line receding velocity and the critical alignment velocity is essential to get the alignment polymer film. In this paper, the contact line receding velocity of a D-A conjugated polymer film, isoindigo and bithiophene (ⅡDDT-C3), was adjusted by solvent vapor content and film-formation temperature. Only when solvent vapor content was 0.3 mL and the film-formation temperature was 90℃, the contact line receding velocity was in accordance with the critical alignment velocity, and the highest degree of alignment was attained in the ⅡDDT-C3 film, with the dichroic ratio up to 4.08. Fibers were aligned parallel with the direction of the contact line receding and the molecules of ⅡDDT-C3 adopted an edge-on orientation with the backbone parallel with the direction of fiber long axis. The π-π stacking distance between adjacent molecules was 3.63 Å.