A novel method of preparing ultrathin poly(ether block amide) membranes

This work deals with a new method of preparing ultrathin poly(ether block amide) 2533 membranes based on spontaneous spreading of a solution of the block copolymer on a water surface. The casting solution used comprised of the copolymer dissolved in a solvent blend (isopropanol/n-butanol, weight ratio 3:1). During the solution spreading, solvent exchange with water occurs which induces polymer precipitation, thereby forming a thin membrane floating on the water surface. The spreading process is accompanied by evaporation of solvent due to its volatility, but the solvent–nonsolvent exchange is primarily responsible for polymer desolvation during membrane formation. The formation of a uniform and defect-free membrane was found to be determined by the solvent system, polymer concentration in the casting solution and temperature. Substantially defect-free membranes as thin as 0.3 μm were prepared. The membranes were tested for gas permeation, and it was shown that the membranes could be used for CO2/N2 and O2/N2 separations that are relevant to greenhouse gas emission control. At 25 °C and a feed pressure of 345 kPa, a carbon dioxide permeance of 350 GPU and a CO2/N2 permeance ratio of 35 were obtained with a 0.7 μm thick poly(ether block amide) membrane.