In this work, the contribution of internal coagulant to morphology evolution of hollow fiber membranes was investigated. Polyacrylonitrile was used to make hollow fiber membranes. Ethanol distillated water/DMSO solutions with different compositions were employed as internal coagulants. Nonsolvent/solvent/polymer ternary phase diagram were constructed experimentally through measurement of cloud points. According to the SEM images captured from cross-section of produced fibers, with increasing solvent concentration in the bore fluid an internal skin layer with lower thickness was observed. This can be interpreted by decrease of nonsolvent strength and hence, delayed phase demixing. Additionally, it was found all internal skins of hollow fibers were pore-free regardless of internal coagulant composition. However, with increasing solvent concentration in the bore fluid, size of the macrovoids increased and geometry of hollow fiber cross section became more corrugated. The latter can be investigated based on Buckling instability theory. KEYWORDS: hollow fiber membrane, composition of internal coagulant, phase diagram, spongelike morphology, fingerlike morphology.
