Evolution of nano-particle distribution during the fabrication of mixed matrix TiO₂-polyimide hollow fiber membranes

The purpose of this short note is to report, for the first time, the effect of elongational drawing on TiO₂ nano-particle distribution in hollow fiber membranes. The results shown in the short manuscript have multiple applications and impact for the fundamental understanding and development of hybrid solid composite fibers and mixed matrix hollow fiber membranes. TiO₂ nano-particles with sizes around 300-400 nm are doped directly into the polyimide solution before spinning. The evolution of membrane morphology and nano-particle distribution has been investigated by SEM-EDX with an increase in elongational draw ratio. It is found that TiO₂ nano-particle distribution across the membrane wall varies from convex to concave profiles depending on elongational draw ratio. In other words, high elongational draw ratios result in particles moving radially inward to the bore fluid side and radially outward to the outer coagulant side. Therefore, one can control membrane morphology, particle distribution, and separation performance via the manipulation of elongational draw ratio with the aid of shear stress induced by dope flow within the spinneret and die swell out of the spinneret.