Porous polymeric films with fine pores in the range from micrometer to sub-micrometer or nano scale order have attracted much attention for various applications, such as membrane separation and purification, solid supports for sensors and catalysts, scaffolds for biological cells, low-dielectric constant materials for microelectronic devices, and battery separators in fuel cells and lithium ion batteries. Recently, phase separation in immiscible polymer blend solutions to prepare porous material has been of great interest due to the simplicity and cost-efficiency of the process. Phase separation in immiscible polymer blends is induced by evaporating the solvent (solvent quenching). It has been known that the dispersed domain (droplet) size and its density can be changed by the coalescence of domains during the phase separation, and the process often results in low domain density and large domain size. Various factors for determining the dispersed domain size and the density, such as solvent type, concentration, molecular weight of the polymer, and weight ratios of polymers have been identified. However, there still remains a great challenge in controlling the pore size and pore density and clarifying the formation mechanisms of porous structures due to the versatility of polymer blends' morphologies.
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