Precipitation of Nylon 6 membranes using compressed carbon dioxide

Membrane formation using a compressed antisolvent is analogous to conventional immersion precipitation using liquid nonsolvents and introduces pressure as an additional variable for tailoring the membrane microstructure. Thin films of a semicrystalline polyamide, Nylon 6, were precipitated from 2,2,2-trifluoroethanol by exposing the incipient membrane to compressed CO2 antisolvent at 35°C and variable pressures up to 173.4 bar. Membrane structures dominated by liquid–liquid (L–L) and solid–liquid (S–L) demixing processes were observed as a function of precipitation conditions. Interpretation of the resulting membrane morphologies was based on structural features observed for traditional phase inversion processes and reflected the relative rates of L–L and S–L demixing as a function of the pressure-dependent strengths of the solvent and antisolvent. The ability to tailor the morphology of a semicrystalline membrane using compressed antisolvent suggests an alternative to current CO2-based polymer impregnation techniques, which require solute solubility in CO2, for the generation of composite thin films and membranes.