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

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 ((V) over bar (o)) and average ScCO2 in-diffusion velocity ((V) over bar (i)) through the interface between the casting solution and ScCO2, (V) over bar (o)-(V) over bar (i). 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 (V) over bar (o)-(V) over bar (i) resulted in the increased trends of pore size and porosity of the membrane with the increases in polymer concentration, ScCO2 pressure and temperature. (C) 2013 Elsevier B.V. All rights reserved.