| Ultra-thin and virtually defect-free polyimide hollow fiber membranes were formed using a "dry/wet" type spinning solution. Fibers were spun from the commercially available polyimide, Matrimid{dollar}sp{lcub}circler{rcub}{dollar}, using a dry-jet, wet quench spinning apparatus. Spin dopes were comprised of volatile and non-volatile solvents, polymer, and non-solvent. The influence of dope composition, spinning parameters, and dehydration procedures on the membrane morphology and performance was investigated. Without post-treatment, the fibers exhibited skin thicknesses less than 1000 A and O{dollar}sb2{dollar}/N{dollar}sb2{dollar} selectivities within 90% of those determined for dense, solution-cast films. The 250 {dollar}mu{dollar}m O.D./125 {dollar}mu{dollar}m I.D. fibers were spun at take-up rates comparable to those used in commercial processes and had macrovoid-free morphologies.; A new characterization technique has also been developed where a permeating gas is held at constant transmembrane pressure while the average pressure in the porous support of an asymmetric membrane is varied. This alters the mean free path of gas molecules permeating through the substructure while maintaining a constant driving force for permeation. This technique characterizes the magnitude of the substructure resistance and its pressure dependence, thereby providing a means to compare the morphologies of different membrane samples. Well defined composite-laminate membranes were constructed to validate this technique, which was subsequently used to characterize the substructures of the hollow fiber membranes formed in this work.; Two additional rapid characterization techniques have been developed for use before fiber dehydration (i.e., wet fibers). These techniques probe the membrane skin layer with aqueous solutions of disperse dyes and poly(ethylene glycol), respectively. Fiber skin integrity can be characterized using these techniques prior to lengthy downstream processing (i.e., solvent exchange, drying, and post-treatment), providing quick elucidation of membrane skin morphology.; Finally, a qualitative model describing the skin layer morphology of phase inversion membranes has been developed. This model arose from observed differences in the permeation characteristics of highly sorbing gases between bore and shell side feeds. It is proposed that the skin layer contains an asymmetric distribution of unrelaxed volume introduced during the formation process. This model has been successfully tested with CO{dollar}sb2{dollar}/CH{dollar}sb4{dollar} permeation measurements conducted at varying temperatures and feed configurations. |
