The document describes experiments to create a tapered porous structure in anodic aluminum oxide (AAO) tubular membranes for use in hemodialysis. It outlines procedures for a two-step anodization process using different electrolyte solutions and voltage parameters at each step. Analysis of results from initial experiments showed that membrane thickness increased with voltage and time during second anodization. Future work proposed repeating experiments while systematically varying time parameters to optimize pore size around 20nm and thickness near 60μm.

1. Tapered Porous Structure in Anodic Aluminum Oxide (AAO) Tubular Membrane using a Two-Step Hard Anodization Process Elkin Mejia February 5, 2008

2. Outline Background Objective Procedure Processing Parameters Trend Analysis/Conclusions Future Work

3. Background: Hemodialysis Semi-permeable Membrane: Separates waste from needed proteins and blood cells BLOOD: Enters Tube Side Red Blood Cells White Blood Cells Albumin (Protein) WASTE: Urea (small) Creatinine B2 Microglobin (middle) Phosphate Dialysate: Enters Shell Side, removes

4. Background: Anodization Electrolyte process used to increase thickness of the natural oxide layer on the surface of a metal Source: Elizabeth Grasing

5. Background: Anodization Anodic Aluminum Oxide (AAO) Contains an array of nanometer-sized pores Anodizing of an Aluminum Substrate: Porous Material: Extremely well ordered honey comb structure pore arrays

6. Background: Anodization Anodization ranges: (A) Low Field Anodization (0 to 10 V) (B) Mid-Field Anodization (10-40 V) (C) High Field Anodization (40-150 V)

7. Background: Membrane Comparison Current Membranes acting as artificial kidneys: Synthetic Polymers Anodic Aluminum Oxide (AAO) Membranes: Non-uniform and Irregular shape Circular and Regular shape

8. Objective Study the effect of transitioning the anodization of aluminum from low to high voltage Pore structure/diameter Remove a larger percentage of waste at a faster rate. Restrict a wide range of molecules that are needed by the human body Membrane thickness Facilitate mechanical handling Compliments fluid separation applications Goal: Pore size ~ 20 nm Goal: Thickness ~ 60 µm

9. Procedure: Processing Stages Source: Elizabeth Grasing Source: Elizabeth Grasing Main Chamber As-Received Tube After Electro-polishing Addition of Polymer Coating 1st Anodization: (Pore Diameter/ Dimple formation) Barrier Layer Etching 2nd Anodization : Pt.1 (Protective Porous Oxide Layer is produced) Pt. 2 (Membrane Thickness Growth) Removal of polymer Ends Sealed with Parafilm Aluminum Etching Removal of Parafilm

10. Procedure: Processing Parameters Electrolyte Solution: H 2 SO 4 (1 st Anodization) H 2 C 2 O 4 (2 nd Anodization) 2) Electrolyte Concentration: 3wt.% H 2 SO 4 (1 st Anodization) 2.7wt.% H 2 C 2 O 4 (2 nd Anodization) 3) Voltage: 12.5 V (1 st Anodization) 20 – 60 (2 nd Anodization, Part 2) 20 V (2 nd Anodization, Part 1) 4) Time: 2-3hours (1 st Anodization) 3-4 hours, 10 hours (2 nd Anodization)

11. Procedure: Instruments Scanning Electron Microscope (SEM): Inner/Outer Pore Structure/Diameter 3) Membrane Morphology Light Optical Microscope (LOM): Membrane Thickness 2) Mercury-in-GlassThermometer: Temperature 1) NI USB-6008 DAQ/Lab View: Current

12. Trend Analysis (A) Transitional Time: Trials C(S11), D(S12) Parameters: 1 st Anodization (3wt.%, 12.5V, 2 hours) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Pt. 2 (2.7wt.%, 60V, 3 hours)

13. Trend Analysis (A) Images of Trials, C(S11) D(S12) ~14 µm ~23 µm

14. Trend Analysis (B) First Anodization Time: Trials G(S15), E(S13) Parameters: 1 st Anodization (3wt.%, 12.5V) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4 hours)

15. Trend Analysis (B) Images of Trials, G(S15) E(S13) ~24 µm ~24 µm

16. Trend Analysis (C) Second Anodization Time: Trials D(S12), G(S15), H(S16) Parameters: 1 st Anodization (3wt.%, 12.5V, 2 hours) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V)

17. Trend Analysis (C) Images of Trials, D(S12) G(S15) H(S16) ~23 µm ~24 µm ~57 µm

18. Parameter/Result Table Parameters Results Trials Stages Electrolyte Concentration Voltage Time Transitional Time (min.) Pd (nm) Mt (µm) C(S11)/D(S12) 1st Anodization 3wt.% 12.5 2 hrs. 2nd Andozation (Part 1) 2.7wt.% 20 30 min. 8 20 14 20 20 23 (Part 2) 2.7wt.% 60 3 hrs. G(S15)/E(S13) 1st Anodization 3wt.% 12.5 2 hrs. 20 24 3 hrs. 20 24 2nd Andozation (Part 1) 2.7wt.% 20 30 min. 20 (Part 2) 2.7wt.% 60 3 hrs. D(S12)/G(S15)/H(S16) 1st Anodization 3wt.% 12.5 2 hrs. 2nd Andozation (Part 1) 2.7wt.% 20 30 min. 20 (Part 2) 2.7wt.% 60 3 hrs. 20 23 4 hrs. 20 24 10 hrs. 22 57

19. Trend Analysis Conclusions: Variation of time in the first anodization did not affect the pore diameter/membrane thickness A pore diameter of 20nm and a thickness of 57µm was obtained at a voltage greater than 12.5 V in the 2 nd Anodization under 24 hours A linear growth rate of the membrane thickness to the 2 nd Anodization (Part 2) time was confirmed

20. Future Work Repeat previous experiments to determine an error bar Objective: Optimize pore diameter (~ 20 nm) and membrane thickness (~ 60 µm) at a high voltage (60V) in an efficient process by varying the time parameters The following are experiments to be conducted in order to conclude a trend analysis in the variation of time (anodization, transitional) and provide sufficient data to prove the above contribution Complete further experiments to complete trend analysis charts Utilize image J software to accurately measure pore diameters Vary the transitional time to determine if the membrane thickness increases Vary the first anodization to study the affect of the pore structure Vary the second anodization time to determine the optimal membrane growth rate

21. Updated Trend Analysis 1 st Round of Membrane Thickness (First/Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.) Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

22. Updated Trend Analysis 2 nd Round of Membrane Thickness (First/Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.) Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

23. Updated Trend Analysis 3 rd Round of Membrane Thickness (First/Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.) Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

24. Updated Trend Analysis Round Comparison - Membrane Thickness (First Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.)

25. Updated Trend Analysis Round Comparison - Membrane Thickness (Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

26. Updated Trend Analysis 1 st Round of Pore Diameter (First/Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.) Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

27. Updated Trend Analysis 2 nd Round of Pore Diameter (First/Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.) Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)

28. Updated Trend Analysis Round Comparison – Pore Diameter (First Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4hrs.)

29. Updated Trend Analysis Round Comparison – Pore Diameter (Second Anodization): Parameters: 1 st Anodization (3wt.%, 12.5V, 4 hrs.) 2 nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.) Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)