In situ studies of the transition from solution to solid film of poly(octylthiophene)

The drying of thick solutions of the conjugated polymer poly(octylthiophene ) (POT) was followed in situ by grazing incidence diffraction of synchrotro n X-rays from the solution surface, with the solvent evaporation rate being controlled by a flow of dry nitrogen gas. It was found that a solid, parti ally crystalline film is formed on the upper surface while the interior is still fluid. The initially formed film is swollen and of restricted correla tion length, but the swelling disappears gradually on further drying. A con siderable fraction (> 20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state on ly during the removal of the last 5% of the solvent. (C) 2001 Elsevier Scie nce B.V. All rights reserved.