Drying behaviour of thick poly(octylthiophene) solutions

Using grazing incidence diffraction (GID) the drying of concentrated solutions of the conjugated polymer poly(octylthiophene) (POT) was follow in situ. The influence of the initial concentration and the ventilation rate of the closed sample cell was studied. For most of the samples, the drying behaviour adheres to a two-stage model; an initial stage with constant evaporation rate, and a finalising stage with only minor evaporation, but with convergence of the crystallinity and spacial correlation to their final values. Concentrated solutions and high ventilation rates promote early formation of a dry skin at the solution-air interphase, effectively acting as a barrier to the solvent flow, thereby slowing down further evaporation from the sample. In this case the distinction between the two drying stages vanishes. For both extremes the unit cell of the initially formed solid phase is swollen and has a correlation length substantially shorter than for the dry polymer.