Development of a simultaneous measurement system for SAXS-WAXD and the thickness of coating films during film formation by solvent evaporation

A system for the simultaneous measurement of small-angle X-ray scattering and wide-angle X-ray diffraction (SAXS–WAXD) and the thickness of a coating film, obtained with an automatic coater, during film formation has been developed. The system was installed on beamline BL03XU at SPring-8. As model specimens, poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymers with different compositions were used to investigate the film formation process during solvent evaporation. First of all, the data correction methods were examined for the coating films during solvent evaporation. Since the scattering invariant was affected by the scattering volume and the absorption of X-rays by the solvent and the copolymer during drying, the scattering invariant should be corrected for the film width and the X-ray absorption of the sample. The polymer concentration was estimated from the thickness of the coating film during solvent evaporation, while the X-ray absorption was evaluated by using the X-ray linear absorption coefficients of the solvent and the copolymer. The results showed that the correction of the scattering invariant is crucial for an exact description of the film formation process during solvent evaporation.