Effects of solvent and nonsolvent diffusion velocities on the morphology of cellular polyetherimide membranes prepared using supercritical CO2 phase inversion

• PEI cellular microporous membranes were prepared by ScCO2 phase inversion method.
• High instantaneous velocity of ScCO2 in-diffusion caused a cellular pore structure.
• Difference of average solvent and ScCO2 diffusion velocities (Vo¯−Vi¯) was calculated.
• The Vo¯−Vi¯ and viscosity explained the PEI concentration effect on membrane morphology.
• The dramatic decrease in the Vo¯−Vi¯ led to big pores and high porosity of the membrane.

Mass transfer kinetics plays a dominant role in membrane morphology. In this study, the effects of polymer concentration, supercritical CO2 (ScCO2) pressure and temperature on the morphology of polyetherimide (PEI) membranes prepared using ScCO2 phase inversion were investigated from the view of the instantaneous velocity of ScCO2 in-diffusion and the difference between average solvent out-diffusion velocity (Vo¯) and average ScCO2 in-diffusion velocity (Vi¯) through the interface between the casting solution and ScCO2, Vo¯−Vi¯. The high instantaneous velocity of ScCO2 in-diffusion at the moment of onset of phase separation led to a cellular pore structure in the membrane. In addition, the dramatic decrease in the Vo¯−Vi¯ resulted in the increased trends of pore size and porosity of the membrane with the increases in polymer concentration, ScCO2 pressure and temperature.

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