Fabrication of a tapered porous structure in anodic aluminum oxide (AAO) tubular membrane using a two-step anodization process

The development of a small pore diameter, large thickness Anodic Aluminum Oxide (AAO) tubular membrane is an ideal product in removing a large percentage of molecular weight solutes at a faster rate and could facilitate mechanical handling during the hemodialysis process. The focus of this research was to optimize the pore diameter and membrane thickness of an AAO tubular membrane in an efficient process by varying the anodization processing parameters. A two stage anodization practice was applied in order to obtain an inner diameter pore of less than 20 nm and a cross sectional thickness greater than 60 mum. It was determined that using a two-step anodization procedure yielded unexpected results in which the inner diameter pore size and voltage did not have a linear relationship as stated in previous literature. It was also established that controlling temperature in the anodization stages and implementing a transitional period in the second anodization stage improved the membrane morphology of the AAO tubular membrane.;The AAO tubular membrane was anodized by controlling anodization time, t, and its influence on the membrane morphology. The time was varied or held constant in three different parts of the process: first anodization time, transitional time and second anodization time. The collected data was examined to determine if the membrane morphology was optimized for the feasibility of the hemodialysis process and other filtration applications. The pore diameter (inner/outer) was imaged using a high resolution Scanning Electron Microscope (SEM) and analyzed using imaging software. The membrane thickness was characterized and measured using a Light Optical Microscope (LOM). The results showed that setting the first anodization stage for 2 hours and the second anodization stage (part 2) for 15 hours yielded a tubular membrane with an inner pore diameter of 18.29 +/- 2.41 nm, an outer pore diameter of 56.21 +/- 11.01 nm, and a membrane thickness of 76.35 +/- 2.87 mum.