Thermal Conversion of Polyamic Acid Gel to Polyimide Solution Having Amino Group Sidechains

time was long enough, the particles in the skin layer were much larger than the original particle size less than 100 nm [10]. A mixture composed of good solvent and poor solvent is used as the solvent used for production of an asymmetric membrane. The composition of the mixed solvent is very important for both the formation of the skin layer by vitrification and the formation of the support layer by liquid-liquid phase separation [20]. DCM is a good solvent and TCE and BuOH are poor solvents for the FPI used. Fig. 9 shows the temporal change of light transmittance after casting of the polymer solution containing the particles. The transmittance decreased immediately after casting and became constant after 70 seconds. The change in transmittance originated in the phase separation in the polymer solution cause by the evaporation of the DCM. This liquid-liquid phase separation would also result in the aggregation of the surface-modified silica nanoparticles in polymer solution. The mixed solvent used this time was suitable for formation of an asymmetric membrane for the neat FPI. However, in order to fabricate an asymmetric MMM, a solvent composition that allows suppression of particle aggregation in polymer solution during solvent evaporation will be required.