Structural anisotropy of poly(alkylthiophene) films

The structural anisotropy of various poly(alkylthiophene) films have been s tudied by X-ray diffraction, using both conventional methods and synchrotro n radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of no nstereoregular material orient with both the main and the side chains in th e film plane. For thick (10-50 mu m) solution-cast films, the degree of ori entation depends strongly on the solvent used for casting, and on the stere oregularity of the polymer, films of stereoregular materials being more ori ented than those of nonregular materials. The most oriented nonregular film s are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50- 500 nm) solution-cast films are more oriented than the thicker ones, and th e effects of different stereoregularity or different casting solvents are s mall. For spin-cast films, the degree of orientation is independent of subs trate and solvent. Spin-cast films of stereoregular material have two diffe rent phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cas t poly(octylthiophene) narrow considerably upon heating.