Residual solvent content in conducting polymer-blend films mapped with scanning transmission x-ray microscopy

Near-edge x-ray absorption fine-structure spectra prove the presence of solvent molecules in conducting polymer films and are used to calculate the absolute solvent uptake of, e. g., 5 vol.% in poly(vinylcarbazole) (PVK) films, which were prepared by solution casting with cyclohexanone as solvent. Nanoscale scanning transmission x-ray microscopy (STXM) reveals a thickness-independent solvent content in a PVK gradient sample due to the formation of an enrichment layer of residual solvent. In polymer-blend films of PVK and poly(3-hexylthiophene) (P3HT), STXM probes a lateral residual solvent uptake, which depends on the composition of the phase-separation domains. For all measurements, oxygen-containing solvent molecules in oxygen-free conducting polymer films are used as marker material, and a significant amount of residual solvent is found in all types of investigated samples.